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SCIENTIFIC = PROCKEDINGS
OF THE
ROYAL DUBLIN SOCIETY.
Ney Series.
% saumnsonlan net ap
MAR 5 1921 269609
Stionay nrase?-
VOLUME XV.
DUBLIN: PUBLISHED BY THE ROYAL DUBLIN SOCIETY, LEINSTER HOUSE, DUBLIN. WIHLTAMS &© NORGATE, ‘14 HENRIETTA STREKT, COVENT GARDEN, LONDON, W.C. 1916-1920.
THE Society desires it to be understood that it is not answerable for any opinion, representation of facts, or train of reasoning that may appear in this Volume of its Proceedings. The Authors of the several
Memoirs are alone responsible for their contents.
Dustin: Printen at tHE University Press ny Ponsonry AND GIBks,
pe Sa neanian ett %
MAR 5 1827
/ . Me & <7
“Seaei| mass CONTENTS
VOL. XV.
No.
I.—The Subsidence of Torsional Oscillations and the Fatigue of Iron Wires when subjected to the Influence of Alternating Magnetic Fields of Frequencies up to 250 per second. By Wiri1aM Brown, B.sc. (January, 1916.) 0
II.—Preliminary Notes on the Carbohydrates of the Musei. By Tuomas G. Mason, 3.A., Dietom. Acric. (February, 1916.)
III.—A New Form of very High Resistance for use with Electro- meters. By Joun J. Downine, M.a., M.R.IA. (February, 1916.)
TV.—On the Path of a small Renal Body moving aan Negligible Acceleration in a Bipolar Field. By Pure Ei. Bunas, B.a., A.R.c.sc.1., and Marous Harroe, M.a., D.Sc. (Sowa 1.). (Plate I.) (February, 1916.)
V.—The Change of Length in Nickel ike of Different Rigidities, due to Alternating Magnetic Fields of Frequencies up to 150 per second. By Witu1am Brown, B.sc. (February, 1916.)
VI.—Osmotic Pressures in Plants. VI—On the Composition of the Sap in the Conducting Tracts of Trees at Different Levels and at Different Seasons of the Year. By Henry H. Dixoy, s0.D. (DUBL.), F.R.s., and W. R.G. Arxins, sc.D. (DUBL.), F.1.C. (March, 1916.) : 6 ah se alae F
VII.—The Verticillium Disease of the Potato. By Guoren H. Preruysrwen, PH.D., B.sc. (Plates II-III.) (March, 1916.) VIII.—On the Boiling-points and Critical Temperatures of Homologous Compounds. By Sypyry Youne, v.sc., r.R.s. (April, 1916.) 1X.—The Subsidence of orsional Oscillations of Nickel Wires when subjected to the influence of Transverse Magnetic Fields up to 200 C.G.S. Units. By Wi11am Brown, B.sc. (April, 1916.) 6 6
X.—On the Hydrocarbons of Bese By Hueu Ryay, p.sc., and
Tomas Dinion, p.sc. (May, 1916.) .
XI.—On Desoxy-Hydrocatechin-Tetramethyl-Kther. By Hueu Ryan, p.sc., and Micuarn J, Watsu, w.sc. (May, 1916.) .
PAGE
29
41
51
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99
107
118
iv Contents.
No.
XII.—The Change of Length in Nickel Wires due to Transverse Magnetic Fields Direct and Alternating. By Witn1aM Brown, B.sc. (May, 1916.)
XIII.—The Subsidence of Torsional Oscillations of Nickel a ren Wires when subjected to the Influence of Transverse Mag- netic Fields up to 800 C.G.S. Units. By Wint1am Brown, B.sc. (May, 1916.) ‘ 5 5 :
XIV.—Note on Laminated Magnets. Py Witu1am Brown, B.sc. (June, 1916.) :
XV.—On the Mode of Occurrence and Origin of the Ouerlies Grenilie of Mullaghderg, Co. Donegal. By Grenvitur A. J. Conn, M.R.LA., ¥.G.S. (Plates IV-V.) (October, 1916.)
XVI.—-An Abnormality in the Arterial System of the Rabbit. By Eipmonp J. Suerny, a.r.c.sc.1. (December, 1916.) .
XVII.—The Fatigue of Nickel and Iron Wires when subjected to the Influence of Transverse Alternating Magnetic Fields. By Witu1am Brown, z.sc. (January, 1917.) : :
XVIII.—The Chemistry of Foul Mud Deposits. By E. A. Lervrs, p.sc., &e., and FLorence W. Rea, z.sc. (January, 1917.)
XIX.—Award of the Boyle Medal to Prorrssorn Hunry Horatio Dixon,
sc.D., F.R.S., 1916. (February, 1917.) : XX.—The Change in vous s Modulus of Nickel with Magnetic Fields. By Wituram Brown, B.sc. (April, 1917.) ;
XXI.—Further Observations on the Cause of the Common Dry-Rot of the Potato Tuber in the British Isles. By Goren H. LErHyBRipGE, B.sc., PH.D., and H. A, Larrerty. (Plates VI- VII.) (June, 1917.) : :
XXII.—The Gymnosomatous Pteropoda of the Coasts of Teall By Anne L. Massy. (Plate VIII.) (July, 1917.)
XXIII.—Spermolithus Devonicus, gen. et sp. noy., and other Pteridosperms from the Upper Devonian Beds at Kiltorcan, Co. Kilkenny. By Tuomas Jounson, D.sc., F.u.S. (Plates IX-XIV.) (August, 1917.) : :
XXIV.—The Genus Zaenitis, with some Notes on the remaining Taenitidinae. By Hurzasntn J. Leonarp, m.sc. (Plate XV.) (February, 1918). 6
XXV.—The Quantitative Spectra of Lithium, Taek, Caesium, a Gold. By A. G. G. Lmonarp, A.R.¢.80.1., B.SC., PH.D., and P. Waeran, a.r.o.so.1. (Plate XVI.) (February, 1918.) .
XXVI.—The Polarisation of a Leclanché Cell. By Fenix EH. Hacxurr, pH.p., and R. J. Funny, a.r.c.sc.1, (March, 1918.) .
PAGE
121
125
137
14!
159
163
Waal
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185
193
228
245
255
274
279
Contents.
No. XXVII.—The Electrical Resistance of Porcelain at Different Tempera- tures. By R. G. Atten, B.Sc. (LOND.), a.R.c.sc.1. (June, 1918.) B . ‘ : : XXVIII.— Observations on the ioral y of Laria leptolepis. By Joszpu Doyte, B.a., msc. (Plates XVII-XVIII.) (August, 1918.) XXIX.—The Insulating Properties of Hrinoid. By R. G. Auten, B.sc. (LonD.), a.R.c.sc.1, (August, 1918.) : ; XXX.—A Disease of Flax Seedlings caused by a species of Colletotrichwm, and transmitted by Infected Seed. By Goren H. Purny- BRIDGE, B.SC., PH.D., and H. A, Larrurry, a.n.c.sc.1. (Plates XIX-XX.) (August, 1918.) XXXI.—The Determination of the Rate of Solution of Aeanesice Nitrogen and Oxygen by Water. Part I. By W. HW. Aveney, D.SC., A.R.C.SC.1., F.J.c., and H. G. Bucxmr, a.R.c.sc.1. (Plate XXI.) (August, 1918.) F XXXI1.—The Absorption of Water by Vulcanized Fibre and Hrinoid on Exposure to Moist Air, and the consequent Change of Electrical Resistance. By R. G. ALLEN, B.sc. Gey A.R.c.sc.1. (October, 1918.) XXXIII.—The Twist and Magnetization of a Steel ‘Tube in a Spiral Magnetic Field. By FP. KH. Hacxert, m.a., PH.D. eon 1918.) $ : XXXIV. —Mahogany, and the Recognition of some of the Different Kinds by their Microscopic Characteristics. By Hxnry H. Dixon, sc.D., F.R.s. (Plates XXII-XLIV.) (December, 1918.) XXXV.—A Disease of Tomato and other Plants caused by a New Species of Phytophthora. By Groren H. Peruysrier, B.SC., PH.D., and H. A. Larrerty, 4.R.c.sc.1. (Plates Ne a (February, 1919). 0 : : XXXVI.—Exudation of Water by Colocasia Hitqionn, By Margaret G. Froop, s.a. (Plates XLVIII.XLVIIa.) (April, 1919.) XXXVII.—The Determination of the Volatile Fatty Acids by an Improved Distillation Method. By JosrpH REILy, u.a., D.SC., F.R.C.SC.1., and Witrrep J. Hicxinsortom. (Plate XLIX.) (April, 1919.) XXXVIII.—Solar Halos seen at Greystones, Co. Wicklow, on September 22nd, 1879; and in Texas and Ohio, U.S.A., on October 8rd, 1917. By Sir Joun Moors, M.A.,M.D.,D.SC.,F.R. MET. SOC. (Plate L.) (April, 1919.) XX XIX.—-Two New Species of Collembola from Ny salad: By Guonee H. Carpenter, D.sc., w.r.1.a. (Plate LI.) (April, 1919.)
b
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vi’ ; Contents.
No. XL.—An Economic Method of) Determining the Average Percentage of Fat in-a Cow’s. Milk. fora Lactation Period. By H. J. ‘Suursy, F.r.c.scz. (Plates LII-LIII.) (May, 1919.) XLI.—The- Comparative Variation of the Constituent Substances of Cows’ Milk. By EH. J, Suepny, rr.c.so1.. (May, 1919.)
PAGE
XLIT.—Possible Causes of Variation in the Quantity and Quality of ~
Cows’ Milk. By EB’). Surnny, r.r.c.sc.1. (May, 1919.) XLII. —The System n-Butyl Alcohol- Acetone—Water. By Josupx REILLY, M-A., D.SC., F.R.c.Sc.1., and Hpaar W. Raupx. (June, 1919.) XLIV.—The Determination of the Rate of Solition of se satire Nitrogen and Oxygen by Water. Part Il. By W. EH. ADENEY, D.SC., A.R.C.S¢.1., F..c., and H. G, Brcxmr, a.R.¢.80.1. (September, 1919.) . XLV.—An Analysis of the Paleozoic Floor of Notth- Kast ieekendl with Predictions as to Concealed Coal-fields. By W. B. Wricut, B.A, F.G.S. (Plate LIV.—Map.) oe 1919.) XLVI.—On some Factors affecting the Goneenencen of Tileoirolyteeh in . the Leaf-sap of Syringa vulgaris. By T. G: Mason, sc.3., ma. (December, 1919.) 5 6 ; XLVII.—On Brown’s Formula for Distillation. By Sypnny Youne, pD.sc., F.R.S. (January, 1920.) ; XLYVIII.— An Apparatus for the Production of High Static Voluaes By J. J. Downing, u.a. (January, 1920.) : XLIX.—Award of the Boyle Medal to Prormssor Joun A. MoGratE ae: M.A., D.SC., F.R.S., 1917. (August, 1920.)
597
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THE
SCIENTIFIC PCE EDINGS
OF THE
ROYAL DUBLIN SOCIETY.
Vol. XV. (N.S.), No. 1. JANUARY, 1916.
THE SUBSIDENCE OF TORSIONAL OSCILLATIONS AND THE FATIGUE OF IRON WIRES WHEN SUBJECTED TO THE INFLUENCE OF ALTER-
NATING MAGNETIC FIELDS OF ee Ee :
“UP TO 250 PER SECOND.
BY
WILLIAM BROWN, B.Sc.,
PROFESSOR OF APPLIED PHYSICS, ROYAL COLLEGE OF SCIENCE FOR IRELAND, DUBLIN. 5
[Authors alone are responsib/e for all opinions expressed in their Communications.
DUBLIN: PUBLISHED BY THE ROYAL DUBLIN SOCIETY, LEINSTER HOUSE, DUBLIN. WILLIAMS AND NORGATH, 14, HENRIETTA STREET, COVENT GARDEN, LONDON, W.C. 1916.
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the Nditor.
THE
SCIENTIFIC PROCEEDINGS
OF
THE ROYAL DUBLIN SOCIETY.
I.
THE SUBSIDENCE OF TORSIONAL OSCILLATIONS AND THE FATIGUE OF IRON WIRES WHEN SUBJECTED TO THE INFLUENCE OF ALTERNATING MAGNETIC FIELDS OF FREQUENCIES UP TO 250 PER SECOND.
By WILLIAM BROWN, B.Sc., Professor of Applied Physics, Royal College of Science for Ireland, Dublin.
[Read NovemBer 23, 1915. Published January 25, 1916. ]
SECTION I.
In November of last year and in January of this year the present writer brought before this Society the results of some experiments on the fatigue and on the subsidence of torsional oscillations of iron wires when they were subjected to the influence of alternating magnetic fields of frequency 50 per second.!
The present communication gives some results on fatigue and on torsional subsidence, obtained with iron wires, when alternating magnetic fields of frequencies up to 250 per second were employed.
For a description of the apparatus used, and of the general methods of experiment, reference should be made to the author’s papers already published.’
1 Scient. Proc. Roy. Dub. Soc., 1915, vol. xiv, No. 26, p. 336, No. 32, p. 393. 2 Ibid., 1911, vol. xiii, No. 3, pp. 31 and 37, and 1915, vol. xiv, No. 26, p. 337.
SCIENT. PROC, R.D.S,, VOL. XV., NO. I, A
2 Scientific Proceedings, Royal Dublin Society.
As in the case of similar experiments with nickel wires,' the iron wires were subjected in every case—unless otherwise stated—to the same longitu- dinal load, viz., 1°5 x 10° grammes per sq. centimetre, which corresponds to the middle value of the loads employed in previous work on iron wires.
It has been shown, for the case of iron wires, that the magnetic field which must be round the wire in order to get the maximum effects for torsion, fatigue, and subsidence of torsional oscillations is independent of the longitudinal load on the end of the wire.’ This is not so in the case of nickel wires where the magnetic field changes with the load, so that in all the pre- sent experiments the one magnetic field, 2°8 c.g.s. units, which gives these maximum effects was used.
The iron wires employed were each 226 ems. long, and 0:163 cm. in diameter; and the millimetre scale for reading off the amplitude of oscillation in the subsidence experiments, or the steady deflection in the fatigue experiments, was placed at a distance of 167 cms. from the plane mirror on the vibrator or load on the end of the wire. The maximum deflection of the light-spot which was used in the subsidence experiments was at the distance marked 300 on the scale, which corresponded to a torsion or twist of the lower end of the wire equal to an angle of about 5° 10’ on each side of the zero.
In the course of the experiments on “ fatigue,” the direct current through the wire was in each case equal to one ampere.
The wire first tested was in the physical condition in which it was received from the manufacturer, and when measured it was found to have a simple rigidity of about 815 x 10° grammes per sq. centimetre. It was placed in the solenoid with the longitudinal load on the lower end equal to 1:5 x 10° grammes per sq. cm., and was tested (1) for fatigue, (2) for subsidence of torsional oscillation when subjected in both cases to continuous (D.C.) and alternating (A. C.) magnetic fields of value 2°8 c.g.s. units.
The results obtained for the fatigue with the different values of the frequency are shown in Table I, and two of the sets of observations are shown in the form of curves in fig. 1. In the table, d means the steady deflection of the light-spot on the scale, and F' the fatigue, and the frequency of the magnetic field is indicated by 2 = 50, &e.
1 Scient. Proc. Roy. Dub. Soc., 1915, vol. xiv, No, 39, p. 521. 2 Thid., 1910, vol. xii, No. 36, p. 484.
Brown—The Subsidence of Torsional Oscillations. 3
TaBLe I. Rigidity = 815 x 10° grammes per sq. em.
n= 50 n = 100 n = 250 Time Mins. d F a F ad F 0 4 0 4 0 4 0 0-5 3:6 0-100 1 3°4-| 0-150
3°6 0-10 375 0-12 a1 0°282
0 2
3
4 | 3-4 | 0-16 | 3:2 | 0-20 | 2:8 | 0-300 6 | 32 | 0-20 | 31 | 0-23 | 2-8 | 0-300 8
10 | 3:0 | 0-25 | 28 | 0-30 15 | 2-84| 0-29 | 2-8 | 0-30 20 | 28 | 0-30 25 | 28 | 0-30
From the values in Table I it will be seen that, as in the case of nickel
wire, the time taken to attain the maximum fatigue is inversely proportional to the frequency of the applied alternating magnetic field.
Hatigue.
Ce nn a a ee a Mee tt CCE
Bees | ge oe ee
30
Minutes.
Fig. 1. A2
4 Scientific Proceedings, Royal Dublin Society.
In the case of iron, however, the value of the maximum fatigue is the same for all the frequencies; whereas, for nickel, the value of the maxi- mum fatigue iereases with the frequency, up to a certain value of the frequency.’
The wire was tested for subsidence of torsional oscillations in this hard state: it was then taken down and heated, when hanging freely in a vertical position, from the top downwards by means of a broad Bunsen flame. When cold, it was cleaned up, the rigidity measured, and again put into the solenoid and tested for torsional subsidence. ‘The wire was then taken down and the same process of heating gone through, the rigidity measured, and the torsional subsidence again observed, and so on, so that the wire was tested when in five different states of rigidity, as indicated below.
The following five tables (II-VI) give only a few of the values observed, which are perhaps sufficient to show the general trend that the curves would take, with the wire in the various states of hardness, if the values were plotted with the number of vibrations as absciss, and the corresponding amplitudes of oscillation as ordinates.
In the tables, the mark D.C. means that the wire was subjected to the influence of a direct longitudinal magnetic field, and A. C. that it was under the influence of an alternating magnetic field at the different frequencies.
TABLE II.
Rigidity == 815 x 10° grammes per sq. cm.
Ke Gh eee | Beth n= 50 n= 100 n = 250 0 300 300 300 300 30 271 262 264 265 70 237 220 221 223
1 Scient, Proc. Roy. Dub. Soc., 1915, vol. xiv, No. 39, p. 525.
Brown—The Subsidence of Torsional Oscillations. 5
TABLE III. Rigidity = 805 x 10° grammes per sq. cm. A.C Number of Vibrations. D.C n= 50 n= 100 n = 250
0 300 300 300 300 30 256 246 247 248 70 206 187 188 189
The fatigue of the wire was also tested when in the state of hardness indicated in Table III, with an alternating magnetic field of frequency 50, and was found to be 0:095, and was attained in 20 minutes.
TABLE IV. Rigidity = 780 x 10° grammes per sq. cm.
A.C Vibrations, | D-¢ n= 50 | n= 100 n = 250 0 300 300 300 300 30 220 204 204°5 205 70 147 122 128 124
The maximum fatigue in this case (Table IV) was found to be 0-04, and took place in 25 minutes, with an alternating magnetic field of frequency 50.
TABLE V. Rigidity = 770 x 10° grammes per sq. cm.
A.C eee DG n= 60 n=100 | »=250 0 300 300 300 300 30 205 184 182 179 70 124 100 99 98
6 Scientific Proceedings, Royal Dublin Society.
TABLE VI.
Rigidity = 760 x 10° grammes per sq. em.
A.C Vibrations, | D-C n= 50 n= 100 n = 250 0 300 300 300 300 30 180 171 170 169 70 80 78 76 78
From the values in Tables II to VL it will be seen that as the simple rigidity of the wire decreases, the damping or subsidence of the torsional oscillations increases, roughly as a straight line law, and that increasing the frequency of the alternating magnetic field to five times has very little effect on the damp- ing of the oscillations, in each state of hardness. When the wire is fairly hard, as in Tables II, III, and IV, the damping is slightly less when the frequency of the magnetic field is increased ; whereas when the wire is slightly softer, as in Tables V and VI, the damping is slightly increased for increased frequency. The turning-point seems to lie between the values of the rigidity, 780 and 770 x 10° grammes per sq. cm., as will be seen from the following table, in which are collected the amplitudes of the 70th vibration when the wire was in different states of hardness, and for both direct and alternating magnetic fields at the different frequencies; the amplitude of the starting vibration being at the distance marked 300 on the scale in each case.
TaBLeE VII. Rigidity fold grammes D.C.
Perea seme n=50 | n=100 | »=250 815 x 108 237 220 221 293 805 ,, 206 187 188 189 TO! op 147 122 123 124 TO lees 124 100 99 98 760 ,, 80 78 76 75
Brown—The Subsidence of Torsional Oscillations. 7
SECTION IT.
It has already been shown in the torsional subsidence of iron wires that the difference in the amplitudes of the T0th vibration, when the wire is under the influence of a direct longitudinal magnetic field, and when under the influence of an alternating magnetic field of frequency 50 per second, diminishes as the load increases, aud that at a certain load this difference vanishes.: In order, therefore, to ascertain if this principle held with higher frequency alternating magnetic fields, a new wire was taken from the same batch, and tested when it was hard and when it was fairly soft. The experiments made were identical with those described above: the wire was tested when it was subjected to six different longitudinal loads and when under the influence of a direct magnetic field, as well as under that of alternating magnetic fields of frequency 50 and 250 per second, the field strength in each case being 2°8 c.g.s. units.
A few of the results obtained with the wire in the hard state are given in Table VIII, and in Table IX are recorded more detailed observations obtained when the wire was in the soft state, that is, in the latter case there are sufficient values given so that one may draw the curves if required.
Tasie VIII. Rigidity = 812 x 10° grammes per sq. cm. Load in Number of aoe eremmes Vibrations. DCs per sq. cm. n= 650 n = 250 1 x 108 0 300 300 300 70 238 221 226 a gf Oh | et a eo 300 70 237 220 221 Reger Rana leesco 300 | 300 70 238 213 217 SMa teen eda aL ONIN |eilracoul™| aon aoomm|lin sa00l. 70 298 210 14 Peery US em A caooy etaoom,| S00 70 225 208 211
1 Scient. Proc. Roy. Dub. Soc., 1915, vol. xiv, No. 32, p. 398,
Scientific Proceedings, Royal Dublin Society.
TABLE IX.
Rigidity = 770 x 10° grammes per sq. cm,
Load in AN grammes Name of D.C per sq. cm. Vibrations. Paes Des 0 300 300 300 10 274 259 261 0°5 x 10 20 251 225 229 50 193 161 157 70 163 116 125 0 300 300 390 10 269 260 258 ORs, 20 242 225 222 50 177 148 145 70 143 111 110 pe 0 300 300 300 10 263 255 252 COM. 20 281 217 214 50 159 135 183 70 125 100 96 0 300 300 300 10 262 254 250 Ope 20 929 216 211 50 155 136 130 70 120 100 95 oAe 0 300 300 300 10 256 252 248 Sait 20 219 213 206 50 139 129 121 70 103 92 86 0 300 300 300 10 250 249 244 4 ) 20 209 208 200 50 124 121 114 70 87 84 78
Brown— The Subsidence of Torsional Oscillations. 9
From the values in Table VIII it will be seen that the damping of the torsional oscillations is increased slightly by an increase in the load: by comparing the amplitudes of the 70th oscillation in each case. When the longitudinal load is increased four times, there is a decrease of about 53 per cent. when a D. C. magnetic field is round the wire, and about 64 per cent. for an A. C. magnetic field of frequency 250 per second. In Table LX, which gives the values for the wire in the softer state, there is a curious result when the light load is used, that is, there is less damping of the torsional oscillations with an A. C. magnetic field of frequency 250 than with an A.C. field of frequency 50 per second, which is the reverse of what occurs with the higher loads. In fact, a soft wire with a small load seems to behave in the same way as a hard wire under all loads. The damping of the torsional oscillations is much more pronounced when the wire is soft than when it is hard; and by taking the same range of loads as was taken above for the hard wire, that is, from 1 x 10° to 4 x 10° grammes per sq. cm., the amplitude of the 70th oscillation is decreased about 40 per cent. for a D. C. magnetic field and about 30 per cent. for an A.C. magnetic field of frequency 250 per second.
The effect of an increased longitudinal load in changing the subsidence of torsional oscillations is better seen from Table X, which gives in each case, for six different values of the load, the difference in the amplitude after 70 complete vibrations when a D. C. magnetic field was round the wire, and when A. C. magnetic fields of frequencies 50 and 250 per second respectively were applied.
TABLE X.
Rigidity = 770 x 10° grammes per sq. em.
Differences. Load in grammes per sq. cm. x 10°. 0°5 1:0 | 15 2 3 | 4 es Cor alersie \imeooye | 20 Ju | 3 D: a aL cy a0 || 8B || 29. | Bs | 17 | 9
These values are shown as curves in fig. 2 (p. 10), which shows that the D.C. and A.C. damping curves would be identical with a load of about SCIENT. PROC. R.D.S., VOL. XV., NO. I. B
&
10 Seientifie Proceedings, Royal Dublin Society.
4-3 x 105 grammes per sq. cm., when the A. C. magnetic field has a frequency of 50, and for a frequency of 250 per second, the load which should be on the wire to make the damping curves identical would be about 5°1 x 10° grammes
D.C. and A.C. curves after 70 vibrations.
per sq. cm. ae IL Pry salle ageless ea ad | 250 i i os Teas
Differences in the amplitude of oscillation from the
1 2 3 4 ss 5 x 10> Longitudinal Loads: grammes per sq. cm.
Fie. 2.
For the sake of comparison with the results given in Section I, and in order to show the behaviour of iron wire when oscillating in a high frequency alternating magnetic field, the whole of the observations obtained are here given in Table XI. The load on the wire was 1°5 x 10° grammes per sq.cm. The values are shown as curves in fig. 3.
Amplitude of Oscillations in Scale Divisions (m.m.).
Brown—The Subsidence of Torsional Oscillations.
Number of Vibrations.
TABLE XI. Rigidity = 770 x 10° grammes per sq. cm. | Cs D.C. n= 50 n = 250 300 300 300 281 277 275 263 255 252 246 235 232 231 217 214 208 | 185 183 179 158 156 159 135 138 141 116 114 125 100 96 = |
Number of Vibrations.
Fie. 3.
11
12 Scientific Proceedings, Royal Dublin Society.
For assistance in making some of the observations I am indebted to My. F. O’Carroll, a Fourth-year Experimental Science Teacher, in training in this College.
Nore.—With respect to the internal friction of materials, I would draw attention to a very interesting paper on “The Internal Friction of Nickel in a Variable Magnetic Field,” by Prof. Ernesto Drago of the R. University of Catania, Italy. (R. Accad. dei Lincei, vol. xxiv, serie 5*, 2° sem., fac. 1°, Roma, Luglio, 1915.)
SCIENTIFIC PROCEEDINGS.
VOLUME XY.
1. The Subsidence of Torsional Oscillations and the Fatigue of Iron Wires when subjected to the Influence of Alternating Magnetic Fields of Frequencies up to 250 per second. By Witx1am Brown, 8.sc. (January, 1916.) 6d.
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THE
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Vol. XV. (N.8.), No. 2. FEBRUARY, 1916.
PRELIMINARY NOTES ON THE CARBOHYDRATES OF THE MUSCI.
BY
THOMAS G. MASON, B.A., Dretom. Agric.
[ COMMUNICATED BY PROFESSOR HENRY H. DIXON, SO.D., F.R.S. |
[Authors alone are responsible for all opinions expressed in their Communications. }
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Jil
PRELIMINARY NOTES ON THE CARBOHYDRATES OF THE MUSCI.
By THOMAS G. MASON, B.A., Diptom. AGric., T.C.D.
{ COMMUNICATED BY PROFESSOR HENRY H. DIXON, SC.D., F.R.S. | [Read Novempen 23, 1915, Published Fepruany 17, 1916.]
THE wide divergence of opinion that prevails concerning the carbohydrates of the angiosperms has suggested that an investigation conducted among the Musci would be of great interest, and might shed lheht on the subject of photosynthesis. The work was undertaken early in January, 1914; owing to the war, however, it was found necessary to discontinue it; yet, incomplete as it is, it seemed advisable to place on record the experiments which had been already completed. The Musci chosen for investigation were—
Polytrichum commune. Thudium tamariscinum. Sphagnum cymbifoliwm.
The material has been collected among the hills and woods of the counties Dublin and Wicklow, and the experiments have been carried out in the Botanical Laboratory, Trinity College, Dublin.
Brown and Morris (2), who worked on the leaves of Tropaeolum, arrived
at the following conclusions :—
1. Cane-sugar is the first sugar synthesised by the assimilatory process, and is the starting-point of all the metabolic changes taking place in the leaf.
2. When the degree of concentration of the sucrose exceeds a certain amount, starch commences to be elaborated by the chloroplasts.
3. Sucrose is inverted, and starch converted into maltose before
translocation.
It may be pointed out, however, that their experiments do not exclude
SCIENT, PROC. R.D.S., VOL. XV., NO. I, c
14 Scientific Proceedings, Royal Dublin Society.
the possibility that levulose may be antecedent to the sucrose. They proved that levulose was a down-grade product from sucrose, but failed to show that it was not also an up-grade sugar.
Parkin (7), in his work on the carbohydrates of the foliage leaf of the Snow-drop, came to very similar conclusions, and further showed that :—
1. Only three carbohydrates are present in the Snow-drop leaf, viz., sucrose, glucose, and fructose.
bo
. The ratio of sucrose to hexoses in the leaf diminished from above downwards, so that the hexoses appear to be the sugars chiefly concerned in translocation.
3. During any single day of the spring the percentage of hexose sugars in the leaf remained fairly constant; that of the sucrose, however, increased during the day, and diminished during the night.
A. V. Campbell (8), who traced the diurnal fluctuations in each sugar of
the mangold leaf, came to the following conclusions :—
1. Reducing sugars are the first carbohydrates to be found as soon as daylight begins.
bo
. When the reducing sugars have reached a certain concentration, the excess appears as sucrose.
3. Similarly starch begins to be formed as soon as the sucrose reaches its maximum.
Strakosch (10), who experimented on the leaves of Beta vulgaris, bases his conclusions chiefly on results obtained by microchemical work.
1. Dextrose is the first sugar to appear in the process of assimilation; in the small veins part of it is transformed into levulose.
2. In the larger veins the two hexoses combine to form sucrose.
3. Sucrose is the form in which the carbohydrates are translocated to the root.
Ruhland (9), who also worked on Beta, stated that the sugars wandered from the leaf chiefly as invert-sugar, especially as levulose, to the root, where they combined to form sucrose.
Thus, Brown and Morris, Parkin and Ruhland express the opinion that the sugars are translocated from the leaves as hexoses, while Strakosch, and apparently Campbell, hold that sucrose is the chief form in which the carbohydrates leave the leaves of angiosperms.
What follows is a summary of my preliminary experimental work with the Musci.
Mason—Preliminary Notes on the Carbohydrates of the Musci. 15
(A) QUALITATIVE WorRK. (1) IDENTIFICATION OF SUGARS.
An aqueous solution of the sugars, freed from tannin, gums, chlorophyll, &e., is prepared in the usual way.
A suitable quantity of the material to be examined is immersed in boiling alcohol for five minutes, in order to destroy the enzymes. The alcohol is decanted off and replaced by distilled water. After twelve hours’ extraction the water is filtered off and added to the alcoholic extract. The alcohol is distilled off, and the chlorophyll thrown out of solution. Basic lead acetate is added to precipitate the tannin and gums, which are removed from the extract.
The excess of lead is neutralized by sodium carbonate; and the deleaded extract concentrated and placed aside for examination. For this the following tests have been employed.
Reducing Sugar.—For the detection of reducing sugars freshly made Fehling solution is quite satisfactory.
Hexoses.— A small quantity of the extract is added to a solution of two parts phenylhydrazine chloride and three parts sodium acetate in twenty parts of water. On heating for half-an-hour a yellow needle-shaped osazone separates from the mixture in the presence of certain hexose sugars, viz., d-glucose, d-fructose.
Dextrose (d-glucose).— A small quantity of the extract is added to an alcoholic solution of diphenylhydrazine. In the presence of glucose the colourless diphenylhydrazones separate from the mixture after several days.
Levulose (d-fructose).— A small quantity of the extract is added to an aleoholic solution of methylphenylhydrazine, to which a few drops of acetic acid have been added. The mixture is heated for ten minutes, and then placed aside. After a couple of weeks the red-yellow osazone appears in the mixture, if levulose is present. As a confirmatory test for levulose Pinoff’s ammonium molybdate solution has been found quite satisfactory.
Maltose—The greater solubility of the crystals of maltose phenylosazone in hot water offers a means of separating it from the less soluble osazones of other sugars, yet the influence of impurities modifies its character so greatly that this means of identification is often rendered inconclusive.
The increase in the amount of copper reduced after treatment with takadiastase is undoubtedly the most reliable means of identifying maltose.
Sucrose.—Sucrose is easily identified by means of the use of invertase. The study of the enzymes offers a means of checking the results derived by the above methods.
o2
16 Scientific Proceedings, Royal Dublin Society.
Starch.—In order to detect the presence of starch, the material which has been immersed in boiling alcohol for a few minutes is then placed aside till decolorized. After decolorization it is washed and placed in a 10 per cent. solution of chloral hydrate for six hours. Dilute iodine in glycerine was then used for the detection of starch granules.
Polytrichum commune.
Hexoses. — Both dextrose and levulose were detected.
Disaccharides.—The presence of sucrose is indicated by the increase in copper reduction on treatment with invertase under suitable conditions, details as to which are given with the quantitative work.
CuO reduced after 1:0182 = » before 0:6975.
The presence of maltose was demonstrated by the following experiment, 100 cc. of previously inverted extract are treated with 0:2 g. of taka- diastase for 48 hrs. at 34°, and the copper reduction again noted.
CuO reduced before 1°032 = 5 after 1:143.
P. commune is probably one of the most highly specialized of the Musci ; in its massiveness it approaches the vascular plants. The stem often reaches a length of more than twenty centimetres. ‘The leaves, which are confined to the upper part of the stem, have a thick midrib. On the upper surface are a series of vertical lamellae. These lamellae are responsible for nearly the whole of the assimilation of the leaf, and, in fact. of the entire plant, for, with the exception of the very top, the stem is without chlorophyll. There is much starch in the cells of the lamellae, but the rest of the leaf is com- paratively destitute of it. In the aerial stem is a thick-walled cylinder much of which is composed of starchless elements, which are apparently living. Outside of this lies a thin hydrom mantle (Tansley and Chick (11)). This hydrom mantle is surrounded by a layer of cells from one to two cells thick, which are densely filled with starch. Next to these cells a layer of thin- walled starch-free typical sieve-tubes occurs, rarely more than one cell thick. These leptoids are followed by a layer of very starchy cells, scarcely differentiated from the cortex, which also contains an abundance of starch.
The hydrom mantle and leptom are in communication with similar elements in the leaf trace. .
Thuidium tamariscinum.
This plant is a small fern-like moss, growing in large mats in woods.
Mason— Preliminary Notes on the Carbohydrates of the Musci. 17
Heaxoses.—Dextrose and levulose are present. Disaccharides.—That sucrose is present is shown by the following
figures :—
after inversion = 0°9324.
Cams Cue weuwee before inversion = 0°3485.
Typical lamellate crystals of maltosazone were entirely absent; on the other hand, a homogeneous yield of acicular crystals, insoluble in hot water, was produced on treatment with phenylhydrazine. On adding a trace of pure maltose to the extract, typical maltosazone could usually be detected after from three to five weeks. The presence of maltose, even in small quantities, is thus rendered improbable.
Starch was totally absent in both leaves and stem.
Sphagnum cymbifolvwm.
Hexoses.—Dextrose and levulose occur.
Disaccharides.—The presence of sucrose is demonstrated by the follow- a f 0:3770 : ( before inversion = 0°3770.
Crome Quo reduces, (after inversion = 0°8454.
The presence of maltose was not brought to light by the use of phenylhydrazine.
Starch is absent from the leaves, but has been found in minute quantities in the stems of some of the material.
Thus dextrose, levulose, and sucrose have been found in all the material examined, and maltose in those containing any appreciable quantities of starch.
(2) IDENTIFICATION OF ENZYMES.
General Method of Preparation.—The material to be examined is immersed in 95 per cent. alcohol for thirty minutes; when freed as far as possible from the alcohol it is slowly dried at 30°C. The dried material is reduced to a fine powder, and placed aside for examination.
By means of the above treatment it was found that the plants were freed from much of their sugars.
The decanted alcohol contains an abundance of tannin.
Invertase.
Our knowledge of the invertase of the flowering plants is now fairly extensive. Special attention may be drawn to the works of Ruhland (8), and Kastle and Clarke .5).
‘The object that has been held in view here is not so much an examination of the enzyme under different conditions, or a comparison with the invertase
18 Scientific Proceedings, Royal Dublin Soctety.
from other sources, as merely to demonstrate its presence and record its distribution.
A 1 per cent. sucrose solution has been employed, and to this the powdered leaf is added.
The following measures were adopted in order to minimize as far as possible all sources of error :— i
1. The sucrose solution was tested for reducing substances before each experiment.
2. ‘Voluol was used as an antiseptic.
3. All flasks were sterilized by heat.
4, The nature of the reducing sugars produced was determined by means of phenylhydrazine.
Two flasks were used in the following experiment :—
The first contained 50 c.c. of a 1 per cent. sucrose solution, to which 2 grams of the leaf-powder of Polytrichum had been added. It was boiled to destroy the enzymes, and furnished a means of making allowance for any sugars the leaf-powder might contain.
A second flask containing 50 cc. of a 1 per cent. sucrose solution was boiled, thus ensuring against any active material that might exist in either the sucrose solution or in the flask. It was then cooled, and the 2 grams of leaf-powder were added.
After four days’ incubation at 35° the sugar solution in each flask was filtered from the leaf-powder, which was thoroughly washed with distilled water, and made up to 100c.c. The following figures show that the leaves of Polytrichum commune contain an active invertase :—
Grams CuO reduced before incubation by 100 c.c. of 1 per cent. sucrose F ‘ 5 : 5 3 O00, Grams CuO reduced after four days’ incubation . = 1°45.
For the detection of the invertase in the various parts of the stem of Polytrichum, and in other mosses, two test-tubes are used: each is half-filled by a1 per cent. sucrose solution ; to one a small quantity of the leaf-powder is added, and the whole is boiled for several minutes, cooled, toluol added, corked, and incubated at 34°. The other test-tube is boiled before the leaf- powder is added, and then treated in a similar manner to the first. After twenty-four hours’ incubation, both test-tubes are examined for reducing sugars with freshly made Fehling solution and phenylhydrazine.
In P. commune invertase has been found both by day and night, and in all parts of the stem; even after the plants had been subjected to four days’ darkness its presence could be detected.
Mason—Preliminary Notes on the Carbohydrates of the Musci. 19
It is strange that in the juice squeezed from plants that had been frozen by means of liquid air, no invertive action could be detected. This may be due to the fact that the tannin had not been removed as it is in the alcoholic treatment.
Other Musci in which invertase has been detected are :-—
Sphagnum cymbifoliwm. Brachythecium riwulare. Dicranus majus. Thurdium tamariscinum. In all these mosses there is no difficulty in detecting the enzyme; even after four hours appreciable quantities of reducing sugars can be detected ; in Sphagnum this is not always the case.
Diastase.
The material under examination was treated in much the same way as that for invertase. A 0:2 per cent. solution of potato starch was used. The following measures were taken to eliminate errors :—
1. The starch solution was tested before use for reducing sugars.
2. Toluol was used as an antiseptic.
3. Freshly prepared Fehling solution was employed to detect the reducing
sugar or sugars formed.
4, The same system of checking was used as for invertase, two flasks being
employed, in one of which the leaf-powder was boiled.
5. The starch-paste after incubation was filtered off and tested with liquor
iodi and Fehling solution.
6. Phenylhydrazine was employed in order to determine the nature of the
sugar or sugars resulting from the hydrolysis.
In the following experiment 0:2 gram of leaf-powder was added to 50 cc. of a 0°2 per cent. solution of starch, and incubated at 30° :—
16 hours. | 48 hours. Iodine Colour 1329. | Iodine Colour | 4). Reaction. Hebling' ppt. Reaction. STS 1a P. commune, purple trace brown marked
after three days’ dark- ness.
Sphagnum cymbifolium, collected at dawn. blue none blue none
20 Scientific Proceedings, Royal Dublin Society.
The osazone crystals produced by the Polytrichum solution consisted of a very few typical hexose tufts, and a great number of hedgehog-like erystal- line groups, which, it seems likely, are largely, if not altogether, composed of maltosazone; this view is supported by the fact that when pure maltose is added to the solution, there results a large addition of these crystals. ‘They are fairly soluble in hot water, and have often been found thrown down from apparently pure maltose solutions, but in a mixed hexose-maltose solution it often seems as though the two types (viz., glucosazone and maltosazone) graded into one another. From the presence of hexose osazones in the incubated solution we may infer the presence of diastase and maltase in the leaves of P. commune.
Maltase.
In the detection of maltase the same precautionary measures were taken.
Two grams of the powdered leaf were added to 80 c.c. of a 0°38 per cent. solution of maltose. After forty-eight hours’ incubation at 38°, both flasks were examined for reducing sugars.
50 c.c. of unboiled solution reduced, 0°35 g. CuO. 50 ¢.c. of boiled solution reduced, 0°29 g. CuO.
The above figures indicate the presence of an enzyme capable of converting maltose into glucose.
The presence of maltase in P. commune is most interesting ; its distribution among the vascular plants has not yet been widely demonstrated. Brown and Morris’ failure to find it in the leaves of Tropaeolum may be due to the fact that in that plant maltose is translocated from the leaves, so that maltase would not be required till the sugar has arrived at its destination.
B. QUANTITATIVE WORK. METHOD OF ESTIMATION.
The fresh material is immediately immersed in alcohol, and boiled for ten minutes to destroy the enzymes.
A small quantity of calcium carbonate is added to prevent inversion by the acids of the plant.
After twenty-four hours’ extraction the alcohol is decanted off. and to the moss is added cold distilled water.
After a further twenty-four hours’ extraction this aqueous extract is added to the alcoholic extract. The residue is washed with warm alcohol, which in due course is added to the previous extracts.
A further extraction is found to contain neither sucrose nor reducing sugars.
Mason—Preliminary Notes on the Carbohydrates of the Musci. 21
On distillation of the alcohol the chlorophyll is precipitated, filtered off, and washed.
The extract is next treated with the minimum amount of basic lead acetate, and a little alumina cream. After the removal and washing of the precipitated gum and tannin, the excess of lead is removed by sodium carbonate. The deleaded filtrate is next concentrated, and made up to the required volume.
This concentration is a source of the greatest trouble, as it involves a browning of the levulose, which renders the use of the polarimeter out of the question. This concentration, however, is rendered inevitable, firstly by the paucity of the sugar present, and secondly by the necessity of using water for extraction in addition to alcohol.
Benedict’s sodium-citrate method (8. R. Benedict (1)) has been used to make the following analysis of P. commune, collected at midday, August 15th. A weighed quantity of the fresh plant (both leaves and stem) was placed in alcohol, and treated as has been above indicated. The dry weight was obtained separately. The sugars extracted from 16-7 g. (dry wt.) were made up to 200 c.c. :—
50 c.c. were used in the estimation of the hexoses, i _ " sucrose, es . 5 maltose, and 50 c.c. were placed aside to be used if required.
100 c.c. of the original solution were found to reduce 0°697 g. CuO.
To 50 c.c. made slightly acid to litmus paper, 6 c.c. of yeast invertase were added. At the end of twenty hours’ incubation, the sugar solution was neutralized, filtered, and made up to 100 c.c.
100 c.c. (after correction for change in concentration) now reduced 1:0181 g. CuO.
The sucrose is calculated from the difference in the amount of CuO reduced before and after inversion.
10181 - 0°6971 =0°321 g. CuO.
As 1 gram of sucrose yields 1:052 grams invert sugar, which is capable of reducing 2°817 grams CuO, the amount of sucrose in 100 cc. of the ne see . 0°32] original solution is expressed by the fraction D317 For the estimation of maltose 50 c.c. of the inverted solution are treated with 3 ¢.c. of concentrated hydrochloric acid for three hours on a water-bath; it is then neutralized with sodium hydroxide, made up to 100 c.c., and the increase in reducing power noted. SCIENT. PROC, R.D.S., VOL, XV., NO. II, dD
= 0:1139 g.
22 Scientifie Proceedings, Royal Dublin Soctety.
100 e.c. (allowing for change in concentration) now reduces 1:1622
g. CuO. «. 11622 —1:0181 =0:1441 g. CuO = 0:1138 g. maltose. Amount of CuO
reduced by hexoses therefore is 0°6970 — 0°1900 = 0°507 g.
P. Commune, collected at noon, August 15.
grms. CuO reduced grms. sugar in by sugar in 16°7 per cent. 16-7 grms. moss. grms. moss. Hexoses, G0 1:014 | 0°3623 2-17 Sucrose, is 0°642 0:2278 1°36 Maltose, at 0:2882 0°2276 1-36
The following is an analysis of P. commune after three days in darkness.
grms. CuO reduced grms. sugar in by sugar in 15°5 per cent. 15:5 grms. moss. grms. moss. Hexoses, ar 0°8655 0°3102 2-00 Sucrose, ne 0-2578 0:0915 0:59 Maltose, 30 0°3101 0:2450 1°58
The great decrease in the total sugars, especially of the sucrose, is very noticeable. Experiments were also carried out to show the distribution of the sugars in leaf and stem. In order to bring into prominence the amounts of the various sugars that are present in the assimilating and non-assimilating parts of the plants, the tip of the stem, which contains a certain amount of green tissue, has been placed aside, and does not figure in the analysis of either leaf or stem. Owing to the time required to separate the leaves with their sheaths from the stem, it has been impossible to express the results as percentages, since inversion of sucrose would take place, if the separated parts were kept till ready for weighing. It has, therefore. been necessary to express the results of the analysis as ratios,
Mason—Preliminary Notes on the Carbohydrates of the Musci. 28
P. commune.
Hexose. Sucrose. Maltose. | Place | ; gathered. grms. CuQ| grms. |grms. CuO} grms. grms. CuO] grms. in Sugar in| Ratio. in Sugar in | Ratio. in Sugar in | Ratio. 100 c.c. | 100 c.c. 100 c.c. | 100 c.c. 100 c.c. | 100 c.c.
0:4040 | 0:1448 1 0°8781 0°3099 | 2:14 | 0-0833 | 0:0658 | 0-45 | Tibradden
Wood Leaf —— = — OSES eae S| ee 5/8 =e 04855 | 0-1740 | 1 1:0736 | 0°3811 | 2-19 | 0°1123 | 0-0887 | 0-51 pine oods.
0-472 | 0-1711 | 1 | 0-0914 | 0-0325 | 0-19 | 0-1429 | 0-1129 | 0-66 | Tibradden Wood.
Oe ! a bit
0-4968 | 0-1781 | 1 | 0-1203 | 0-0427 | 0-24 | 0-1622 | 0-1282 | 0-72 weppare
In the above analysis the alteration in the hexose-sucrose ratio indicates an inversion of sucrose, as sugar passes from the leaves to the stem.
This inversion, which is rendered more probable by the presence of invertase in the leaf, points to the carbohydrates being translocated to a large extent in the hexose form.
In considering the conditions which prevail in the leaf, it is difficult to see how the hexoses can be responsible for synthesis of sucrose, as in the presence of invertase a very high concentration of hexose sugars would be needed to bring about its formation; such a high concentration is negatived by the foregoing results.
The next experiment shows the way in which the sucrose in Thuidiwm tamariscinum diminishes when the plants are kept in darkness.
The difficulty of preparing the plants for analysis again renders it necessary to express the results as ratios.
Prepared in the afternoon. After three days’ darkness. es AG | grms. CuO in | grms, sugar in De grms. CuO in | grms. sugar in Ang 100 c.c. sol. 100c.c. | Ratio. | “100 c.c. sol. 100 cc. Hallo: \ | | Hexose, .. 0°3485 | 0°1249 i 03984 | 01428 i Sucrose, .. 0°5839 | 0-2072 1-66 0:2129 0-0756 0°53 } | | | |
24
Scientific Proceedings, Royal Dublin Society.
In dealing with Sphagnum cymbifolium, it has been necessary to bring
up jars of alcohol to the bog for collection, as laboratory cultivation is out of
the question.
Once again, the results are expressed as ratios.
Upper Green Part. Lower Colourless Part. grms. CuO in | grms. sugar in : grms. CuO in | grms. sugar in : T0ee, | wide, |) 228 ||" ag aa, oc, || HAM Hexose, 0°3770 0°1351 1 0°4684 0°1663 1 Sucrose, .. 0°8206 0°2941 2°18 0°4475 0°1587 0-95
The above analysis renders it improbable that the hexoses are antecedent to the formation of sucrose, since here, also, that concentration of hexoses, necessary to bring about the synthesis of sucrose in the presence of invertase, is lacking. The next experiment was devised with the object of ascertaining, if possible, which was the first sugar to be formed after the application of light.
On August 22nd, four jars of moss were collected in alcohol from the mountains at intervals of one and a-half hours. The sun rose at 5.11 A.M., so the first sample was taken at 4.45 aM Only the green tops of the plants were employed, and each sample was taken from the same locality. The result of the analysis, expressed as ratios, is shown on the accompanying table and graph.
Sphagnum cymbifolium,
Time at. which 4.45 a.m. 6.15 a.m. 7.45 AM 9.15 A.M. collected. | grms. CuO reduced | Sugar grms. | Sugar grms. Sugar grms. | Sugar by 100 c.c. in Ratio.| CuO in in Ratio.| CuQ in in Ratio. | CuO in in Ratio. Solution. 100 c.c. 100 c.c. | 100 c.c. 100 c.c. | 100 ec. | 100 c.c. | 100 ¢.c. | | Hexoses, 0°4785 | 0°1715 1 | 0:°3671 | 0:1816 1 0°4793 | 0:°1724 1 0:279 0-1 1 Sucrose, 0:4515 | 0-16 0:9383 | 0-3869 | 0°1373 | 1:048| 0°5316 | O-1887 | 1:094] 0°3552 | 0°1261 | 1-261
Mason— Preliminary Notes on the Carbohydrates of the Musci. 25
The rise in the sucrose graph may be due either to an actual rise in the quantity of sucrose, or to a fall in the amount of hexoses owing to trans- location, respiration, &c. A rise in the amount of sucrose is rendered almost certain, since a fall in the hexoses would involve an enormous diminution
of total sugar.
(1.26)
HEXOSE
aes all 4.45. A.M. 6.15. 7.45 9.15.
The rather strange “hang” in the sucrose graph between 6.15 and 7.45 A.M. may be due to a more rapid inversion of sucrose than formerly ; if such be the case, we must suppose that assimilation increased at a very great rate between 7.45 and 9.15 A.M., or else that translocation became more brisk ; both factors may have been in operation. On the other hand, any slight unevenness in the third sample would be auite sufficient to explain the apparent hang.
It seems fairly clear, however, that sucrose is the first sugar to accumulate on illumination. If it is assumed that the hexoses are the first sugars to be formed in the plastid on exposure to light, it is difficult to see why, instead ot accumulating, condensation to sucrose should be necessary.
26 Scientific Proceedings, Royal Dublin Society.
STARCH.
Marchal (6) has shown that P. juwniperwm, and, in fact, all the starch- building mosses examined, can build up, starch, when artificially fed with solutions of varying concentration of sucrose, glucose, maltose, and lactose; but from the experiments it is impossible to come to any conclusion as to their relative efficiency. In his work he used percentages by weight, but it seems doubtful whether this does not put sucrose at a disadvantage in comparison with the hexoses. In discussing the starch of P. commune, the starch in the lamellae of the leaf and the starch in the stem must be distinguished. ‘The question that naturally presents itself is whether the same sugar is concerned in the formation of both; probably the answer is in the affirmative. If it is so, we are faced with the following possibilities :-—
A.—Sucrose is immediately concerned with the formation of the starch in the lamellae, and the quantities of sucrose that find their way into the stem are concerned solely with maintenance of the starch reserve there; in the last sentence the word “solely” must be emphasized, because the small quantities that occur in the stem would only be adequate provided they were entirely devoted to this work; but that this is not so is shown by the fact that invertase in large quantities occurs in the stem. It is further questionable whether the amount of sucrose which penetrates the rhizome would be adequate even if it was devoted exclusively to this work. It is reasonable therefore to conclude that either maltose or a hexose is respon- sible for the formation of starch. But maltose seems out of the question, since it is not known to arise, except from the hydrolysis of starch, whereas a constant supply from the leaves is necessary for this task. The only sugars that come down from the leaves in quantities anything like sufficient to maintain the starch supply are the hexoses.
B.—If it be granted that the same sugar is concerned in the formation of starch in both leaf and stem, then it follows that small quantities of sucrose in the plastids of the lamellae must be inverted, and that this invert sugar or one of its members must be responsible for the maintenance of starch in the leaf lameliae.
SUMMARY.
1. Dextrose, levulose, and sucrose have been found in all the material examined, whereas maltose is dependent on the presence of starch.
2. Invertase is of wide distribution, whereas diastase and maltase have been found in P. commune alone. Thus their detection is dependent on the presence of appreciable quantities of starch.
Mason— Preliminary Notes on the Carbohydrates of the Musci. 27
3. In P. commune and S. cymbifokiwm the hexoses appear to be the chief form in which the carbohydrates descend the stem.
In reference to the remarks made above concerning the necessity of a high concentration of hexoses in order that sucrose be synthesised under the influence of invertase, it may be pointed out that though the experiments quoted in this work exclude the possibility of a high concentration for the whole leaf, yet they do not demonstrate the absence of a localized high con- centration. This local concentration might exist in the chloroplasts, possibly as a film in contact with the chlorophyll. That this is not so is shown by the following considerations :—
1. The chloroplast would require a selectively semi-permeable membrane to permit the sucrose to diffuse and yet retain the hexose; experiments on starch-formation from hexose solutions negative this.
2. In the chloroplast, or that region of it where the hexose concentration is supposed to be present, there would be approximately 1 per cent. sucrose, and 99 per cent. hexose (the equilibrium percentages of these sugars in the presence of invertase (Visser 12)); this would involve (as analysis has shown) a diffusion of sucrose from the rest of the leaf into the chloroplast ; since more than 1 per cent. of sucrose is present throughout the leat.
3. Ina lamella of P. commune composed of five tiers of cells, in order that sucrose may continue to diffuse away a high concentration is rendered inevitable in the uppermost cells, but a high concentration of sucrose in the cell prohibits the sugar formed in the chloroplast from diffusing out into the vacuole and cytoplasm; this banking up of sucrose involves a higher concentration in the region of hexose concentration than 1 per cent., and this would exclude further synthesis under the influence of invertase; but the energy entering the chloroplast would ensure a continuation of hexose-formation, and if this was unable to proceed to sucrose and so be removed, a banking up of hexose would occur, and so on through the different stages in the synthesis of the hexoses, till at length a stage would be reached where the energy entering the chloroplast would be unable to carry on the process.
If we substitute a high concentration of sucrose for hexose in the chloroplast, we escape all the above difficulties. It should be noted that though invertase has been shown to be present in the leaf, yet it has not yet been demonstrated that it is present in the plastid,
28 Scientific Proceedings, Royal Dublin Soctety.
In conclusion it must be pointed out that the factors that operate in bringing about the synthesis of sucrose in the plant cell are still very obscure. (Robertson, Irvine, and Dobson (8).)
Hudson’s (4) work has rendered it improbable that invertase in aqueous solution possesses this property.
LITERATURE.
1. Benepict, 8S. R.: A Method for the Estimation of Reducing Sugars. Journ. of Biol. Chem., 1911, vol. ix, p. 57.
. Brown, H. T., and Morris, G. H.: A Contribution to the Chemistry and Physiology of Foliage Leaves. Journ. of Chem. Soc., Trans., May, 1893, vol. lxiii, p. 604. 3. CampBeLL, A. V.: Carbohydrates of the Mangold Leaf. Journ. of Agric. Science, Jan., 1912, vol. iv, Pt. 3, p. 248. 4, Hupson, C. 8.: Inversion of Sucrose by Invertase. Journ. of Amer. Vhem., Soc., July, 1914, vol. xxxvi, No. 7, p. 1566. 5. Kastie, J. H., and CLARKE, Mary E.: Amer. Chem. Journ., 1903, vol. xxx, pp. 422-427. 6. Marcuat, El. et Em.: Recherches Physiologiques sur l’amidon chez les Bryophytes. Bulletin de la Soc. Roy. de Bot. de Belgique, 1906, T. xliii, pp. 115-214.
. Parkin, J.: The Carbohydrates of the Foliage Leaf of the Snowdrop, and their Bearing on the First Sugar of Photosynthesis. Biochemical Journ., 1911, vol. vi, Pt. i, p. 1.
8. Ropertson, R. A.; Irvine, J. C.; and Dosson, M. E.: A polarimetric study of the sucroclastic enzymes of Beta vulgaris. Bio-chem. Jour., 1909, vol. iv, p. 258.
9. RuHLAND, W.: Untersuchung uber den Kohlenhydraten von Beta vulgaris. Jahrb. f. wiss. Bot., 1912, Bd. 1,8. 200-257.
10. SrraxoscH, 8.: Ein Beitrag zur Kenntniss des Kohlenhydratstoff- wechsels von Beta vulgaris. Stzb. d. Kais. Akad. d. Wiss. in Wien, Math-Naturwiss. Klasse, Juni, 1907. Bd. exvi, Abt. 1,8. 855.
11. Tansey, A. G., and Cuick, E.: Notes on the Conducting Tissue-System in Bryophyta. Ann. of Bot., 1901, vol. xv, p. 1.
12. VissER, A. W.: Reaktionsgeschwindigkeit und Chemische Gleichgewicht, in homogeneu Systemen und deren Anwendung auf Enzymwirkun- gen. Zeitschrift f. physik. Chem. 1905, vol. li, pp. 257-389.
bo
~T
SCIENTIFIC PROCEEDINGS.
VOLUME XV.
1. The Subsidence of Torsional Oscillations and the Fatigue of Iron Wires when subjected to the Influence of Alternating Magnetic Fields of Frequencies up to 250 per second. By Wituiam Brown, B.sc. (January, 1916.) 6d.
2. Preliminary Notes on the Carbohydrates of the Musci. By Tuomas G. Mason, 8.A., Dipnom. Acric. (January, 1916.) 6d.
DUFLIN: PRINTED AT THE UNIVERSITY PRESS BY PONSONBY AND GIBBS.
THE
SCIENTIFIC PROCEEDINGS
OF THE
ROYAL DUBLIN SOCIETY.
Vol. XV. (.8.), No. 3. FEBRUARY, 1916.
A NEW FORM OF VERY HIGH RESISTANCE FOR USE WITH ELECTROMETERS.
BY
JOHN J. DOWLING, M.A., M.R.LA.,
LECTURER IN PHYSICS, UNIVERSITY COLLEGE, DUBLIN.
[Authors alone are responsible for all opinions expressed in their Communications. |
DUBLIN: PUBLISHED BY THE ROYAL DUBLIN SOCIETY, LEINSTER HOUSE, DUBLIN. WILLIAMS AND NORGATE, 14, HENRIETTA STREET, COVENT GARDEN, LONDON, W.C. 1916.
Price Sixpence.
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EVENING SCIENTIFIC MEETINGS.
Tur Scientific Meetings of the Society are held alternately at 4.30 p.m. and 8 p.m. on the third Tuesday of every month of the Session
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Authors desiring to read Papers before the Society are requested to forward their Communications to the Registrar of the Royal Dublin Society at least ten days prior to each Meeting, as no Paper can be get down for reading until examined and approved by the Science
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[ 29 ]
III.
A NEW FORM OF VERY HIGH RESISTANCE FOR USE WITH ELECTROMETERS.
By JOHN J. DOWLING, M.A., M.R.LA., Lecturer in Physics, University College, Dublin.
[Read NovyemBer 23,1915. Published Frpruary 2, 1916.]
§ 1. THE minute currents met with in many modern lines of research have usually been measured by observing the rate of charging of a system of known capacity with an electrometer or electroscope. There are certain disadvantages in this procedure, and some efforts have been made to devise a “steady deflection’? method, notably by Bronson! and by Campbell. To effect this it is simply necessary to use the electrometer to measure the potential drop across a suitable high resistance, through which the current to be measured passes to earth.
§ 2. There is, however, one serious obstacle to be overcome, namely, that the resistance required for this purpose is usually very large indeed. Thus, if the electrometer gives a full-scale deflection for about =}, volt, and if a current of 10-° ampere is to be measured, we require a resistance of the order of 100 megohms.
Moreover, this resistance must not vary with the current, so that the electrometer deflections may be proportional to the currents being measured. It is also very desirable that the resistance should possess no appreciable temperature coefficient, and that it should be free from polarisation effects. These requirements we may regard as essential; but the utility of the resistance method would be greatly enhanced were it possible to vary the resistance according to the strength of the current to be measured. Thus it would be very useful if the resistance could be constructed to have a definite value, such as 100, 500, 1000, or 5000 megohms: but it would be still more serviceable if it could be altered, while in use, from one to another of these values.
I believe the apparatus now to be described meets these requirements.
§ 3. The method of attaining such high resistances suggested itselt in con- nection with Siemens’ method of measuring a small capacity. In this method
1 Bronson, Amer. Journ. Sc., 1905, 4th Ser., vol. xix., p. 185. 2 Campbell, Phil. Mag., 1911, vol. xxii., p. 301—and.later papers.
SCIENT. PROC. R.D.S., VOL. XV., NO. III. ‘ E
30 Scientific Proceedings, Royal Dublin Society.
a current is passed through a circuit by the alternate charging and discharging of a condenser. If the capacity of the condenser is ¢ farads, and if it be charged and discharged times per second, the charging potential being V volts, it is clear that the current passing is neV amperes. This arrangement
: ; : : 1 is obviously equivalent to a resistance f = mr ohms.
This equivalent resistance will usually be very large. Thus, if ¢ = 001 microfarad = 10 farad, and if m = 10 per second, we obtain :— 1 lig oe 10° ohms = 100 megohms. This is, therefore, of the order required, as we have seen, for the measurement of currents in the neighbourhood of 10° ampere, by a steady deflection method. By varying 7 and c, it is possible to obtain equivalent resistances from 107 to 10% ohms. Indeed, wider ranges may be covered, but the author has not yet tried the method outside these limits.
~ To Earth
§ 4. The apparatus is very simple. In the figure a quadrant electrometer # is shown as ordinarily used with an extra capacity ¢,, connected up to an ionisation chamber J in order to measure the current therein. To this system is further connected the arrangement shown in the lower part of the figure. A and & are two platinum-tipped contact screws, mounted on insulating pillars. Between these is mounted a steel spring, 8, also supported on an insu- lating pillar, and having platinum contact pieces facing those on the screws Aand B. The screws are adjusted so as to allow the spring to vibrate with just sufficient amplitude to make alternate contacts with them. To the spring S is connected one terminal of the condenser ¢, which may con-
Dow.iine—WNew Form of very High Resistance with Electrometers. 31
veniently have a capacity of one-thousandth of a microfarad and be subdivided into smaller fractions.
The vibration of the spring S is controlled by an electromagnet, which is excited by an intermittent current from a tuning-fork or other automatic interrupting device.
§ 5. The action of the apparatus is obvious. On opening the earthing key KX, the electrometer system (HC,) charges up to a steady potential V, such that the intermittent current nc. V drawn off by the vibrating contact is equal to the current 7 being measured, which passes into the electrometer system from the ionisation vessel Z (or other source of current). This is, of course, correct only if the potential to which ¢, is charged at each contact is approximately the same as the electrometer potential. For this to be the case, it is simply necessary that c, should be small compared with «. This condition is readily fulfilled in practice, since ¢, rarely exceeds ‘001 microfarad.
If the above condition is not fulfilled, we sacrifice the simplicity of the relation between the electrometer deflection and the current. As against this drawback we would have the advantage that the electrometer would take up its deflections the more rapidly the smaller we made ¢. On putting this to a practical trial, however, in the case where ¢, and e were equal, it was found that another difficulty was met with. Owing to slight variations in the times of contact of S with A and B respectively, the electrometer deflection was unsteady. As it was not found easy to remedy this, further trials of the apparatus in this way were abandoned.
§ 6. The writer has tested the method over a considerable range, using it to measure ionisation currents in gases drawn from a flame. Each measure- ment was repeated immediately afterwards by the old “rate of charge” method. In all cases a very good agreement was found, provided that the condition mentioned in the previous paragraph was fulfilled. There was one difficulty met with. The electrometer was somewhat unsteady at first. This was found to be due to the faulty action of the contact-breaker ; but on approaching the screws A and B very near together, so as to limit the vibration of S to a very small amplitude, the trouble disappeared.
The largest “equivalent resistance ” tried was limited by the apparatus used by the writer, namely: (1) the smallest condenser (¢,); (2) the slowest interrupting device. The smallest condenser was about 10 microfarad, and the clockwork interrupter gave two interruptions per second. The equivalent
resistance was, therefore, ohms, that: is 5000 megohms,
1 4 33 MO The lowest equivalent resistance tried was 10’ ohms, or 10 megohms. This was obtained by using a capacity ¢, = ‘002 microfarad and a tuning-fork
32 Scientific Proceedings, Royal Dublin Society.
interrupter giving 50 interruptions per second. Several intermediate values were also tried.
With this range of resistances, and an electrometer having a sensibility of about 2000 per volt, it was possible to measure accurately currents between 5 x 107” ampere and 1°5 x 10° ampere. By using even smaller capacities (¢2) and a slower interrupter it should be possible to measure currents less than 10“ amperes. In consequence of the long period of the electrometer needle, it would appear possible that an interrupter which made contact only once every two or three seconds might be employed.
§ 7. An obvious modification is to convert the method into a “ zero” or a “compensation” method. This may readily be done by connecting the contact screw A, not to earth, but to a potential dividing device, of which one terminal is earthed. The condenser, ¢, then feeds in an inverse “ compensating ” current (=—7 ¢, v), which tends to prevent the electrometer system charging up under the influence of the current 7 This compensating current may be varied by changing either n, or c,, but preferably by changing v by means of the potential divider. The electrometer readings V, are now proportional to the difference between the current 7 being measured and the “compensation” current. The total value of 7 is obviously
t= C (Ve +).
The advantages of a method of compensation have frequently been recognized in cases where small variations of a comparatively large current, say In an ionised gas, have to be examined; but the method here described appears to the writer to be more satisfactory than any yet tried.
In the practice of the compensation method small values of c, and m are chosen, and a comparatively high potential is applied at A by means of the potential divider. A large electrometer deflection may, therefore, be obtained even when the current 7 is almost balanced by the “compensation” current.
§ 8. It is hoped that the method outlined above may be found of use by other workers. An important advantage found in practice was the economy of time during a set of observations. This was due to the fact that it was generally unnecessary to earth the electrometer between consecutive observa- tions. Any induction effect, for instance, produced on changing the potential of the ionisation vessel J by a moderate amount died away in a few seconds ; and the electrometer seldom required more than half a minute to reach its new position of rest. In certain classes of work this rapidity should be very advantageous.
I have pleasure in thanking Professor M‘Clelland for the interest he has shown in this work.
SCIENTIFIC PROCEEDINGS.
VOLUME XV.
1. The Subsidence of Torsional Oscillations and the Fatigue of Iron Wires when subjected to the Influence of Alternating Magnetic Fields of Frequencies up to 250 per second. By Wiiu1am Brown, B.sc. (January, 1916.) 6d.
2. Preliminary Notes on the Carbohydrates of the Musci. By Tuomas G. Mason, 8.A., Dipnom. Acric. (February, 1916.) 6d.
3. A New Form of very High Resistance for use with Hlectrometers. By Joun J. Downine, M.a., M.R.1.a. (February, 1916.) 6d.
7 DUBLIN: PRINTED AT THE UNIVERSITY PRESS BY PONSONBY AND GIBBS.
THE
SCIENTIFIC PROCEEDINGS
OF THE
ROYAL DUBLIN SOCIETY.
Vol. XV. (N.S.), No. 4. FEBRUARY, 1916.
ON THE PATH OF A SMALL PERMEABLE BODY MOVING WITH NEGLIGIBLE ACCELERATION IN A BIPOLAR FIELD.
BY
PHILIP E. BELAS, B.A., A.R.C.Sc.1., AND
MARCUS HARTOG, M.A., D.Sc. (NUD). aovian Insti
UNIVERSITY COLLEGE, CORK. l =)
Noy; orang \) “Tonal Wee,
[COMMUNICATED BY PROFESSOR WILLIAM BROWN, B.SC.]
(PLATE |.)
[Authors alone are responsib/e for all opinions expressed in their Communications. |
DUBLIN: PUBLISHED BY THE ROYAL DUBLIN SOCIRETY, LEINSTER HOUSE, DUBLIN. WILLIAMS AND NORGATE, 14, HENRIETTA STREET, COVENT GARDEN, LONDON, W.C. 1916.
Price Sixpence.
Roval Bublin Society,
FOUNDED, A.D. 1731. INCORPORATED, 1749.
EVENING SCIENTIFIC MEETINGS.
Tux Scientific Meetings of the Society are held alternately at 4.30 p.m. and 8 p.m. on the third Tuesday of every month of the Session
(November to June).
Authors desiring to read Papers before the Society are requested to forward their Communications to the Registrar of the Royal Dublin Society at least ten days prior to each Meeting, as no Paper can be set down for reading until examined and approved by the Science
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necessary Illustrations in a complete form, and ready for transmission to
the [ditor.
[ 33 |]
IV.
ON THE PATH OF A SMALL PERMEABLE BODY MOVING WITH NEGLIGIBLE ACCELERATION IN A BIPOLAR FIELD.
By PHILIP E. BELAS, B.A., A.R.C.Sc.L., AND MARCUS HARTOG, M.A., D.Sc. (N.U.L), University College, Cork. (COMMUNICATED BY PROFESSOR WILLIAM BROWN, B.SC.) (Puate I.) [Read Novemper 23, 1915. Published Fepruary 28, 1916.] Historical.
Tus investigation originated in the researches of one of us (Dr. Hartog) upon the “Mechanism of Mitosis in the dividing cell.” Struck by the similarity of the spindle form which is assumed by the achromatin fibres of a cell undergoing division with that of inductive dust, when scattered on a flat surface, or suspended in a liquid of lower permeability, between two poles of opposite sign, he was led to develop a theory that at a particular stage in its life-history the cell was the seat of a dual force, like electrostatic, centring on two bodies—the centrosomes—whose field was bounded by the cell wall. The chromosomes were to be considered as portions of matter more permeable (in the broad Kelvin sense) than the medium in which they moved and their orientations in the equatorial plane, discessions and migration to the centrosomes were to be accounted for by the differential action about the two force centres on these aud on the surrounding medium.
This theory we consider to be fully established by the experiments described in a series of papers by Dr. Hartog, and in this our joint paper.
When we were attempting to model the phenomena of mitosis by means of a bipolar magnetic field, we had to consider what would be the path of a small dise of very soft iron if floated in a viscid liquid between the poles of an electromagnet—the disc at no time acquiring observable acceleration.
A more accurate model of the field of the living cell would be obtained by using charged electric spheres; but since climatic and other conditions made electrostatic force inadmissible in practice, the plane section of the magnetic field through the poles, having the same general distribution of energy, was utilized by us. On looking up the literature of fields of force, electrostatic and magnetic, we noticed a remarkable paucity of information.
Asingle North Pole —that useful abstraction—would of course move along
SCIENT. PROC. R.D.S., VOL. XV., NO. IV, F
34 Scientific Proceedings, Royal Dublin Society.
the lines of force to the opposite pole, which statement is equivalent to defining a line of force; but beyond the general statement that a permeable body would always move so as include the greatest number of lines of induction, there was no indication of the actual trajectory. We therefore determined to investigate the problem for ourselves as follows :—
Descriptive.
Our first experiments were made with circular discs of thin charcoal iron, cemented by paraffin to the lower faces of discs of cork or linoleum to float them. The liquid used was water, and the method of observation was to powder the surface with starch or flour so as to increase the frictional resistance and, at the same time, to define the passage of the floating disc by its wake.
Among our preliminary experiments we wish to note three that are well suited for demonstration purposes. A Gillette razor-blade floating on the surface film of water, or gum-water, shows very clearly the relation of our curves to the lines of force of the field, whether homo-polar or hetero-polar. Still better is a light compass needle! pivoted on a pin, attached to a cork float ; the compass-needle is at all points tangential to a line of force, while the float bearing it of course follows such a curve as we have described.
A magnetic shell formed by punching a disk from an annealed Gillette blade, hardening it and magnetizing it in a coil traversed by a strong current, and then attached to a disk of cork, follows the lines of force of the field; this was devised to model the behaviour of a charged body in an electrostatic field, as contrasted with the path of a body more permeable than the medium.
This was unsuited to give accurate records of the path followed. We replaced the water by various viscid liquids, of which glycerine soon showed its superiority, though it has the disadvantage of becoming hydrated during the time of experiment. The disturbing effects of currents and of surface tension were reduced very greatly with this liquid, the latter being noticeable only towards the extreme edge of the trough.
We soon had to replace the floating dises, since, owing to their form, they gave a lurch whenever the exciting current was put on or increased. This was avoided by using a spherical float. Paraffin softened by gentle heat was com- pressed ina bullet-mould; the part adjoining the channel for pouring in lead was melted with a hot needle, and reduced iron pushed in. The sphere measured § inch in diameter, and contained about 0:13 gms. of iron.
We attempted to record the path by covering the trough, through which the magnet poles projected, with a sheet of ground glass, rendered transparent
* A more permeable body and a magnet of course follow similar paths, since the lines of induction in the former make it a magnet for the time being.
Betas and Harrog—Path of a Small Permeable Body, &c. 35
by wetting with glycerine, and tracing the path with a pencil; but apart from other difficulties, the error of parallax was so great and unequal that we abandoned it.
Final Method.
Ultimately the following method of record gave us results freer from error than the experimental conditions to be recorded.
A strongly built }-plate camera (see Plate I.) was bedded on its side in a teak board, excavated to hold it firmly, and provided with a backward exten- sion carrying leaden weights to prevent overbalancing. Attached to the lens is a right-angled prism, looking directly over the centre of the field, so that it is reflected and focussed on the ground-glass screen of the camera, which is reversed. This permits dots to be made by the “recorder” with a pencil at the successive portions of the screen occupied by the image of the zenith of the spherical float (which is spotted with black); and it is these dots that are reproduced in our figures.
Needless to say, the camera and prism must be so adjusted that the horizontal face of the latter is parallel to that of the fluid, and that the axes of the camera are parallel to those of the trough, so that all perspective distortion is avoided. The prism used was a first-class one by Beck, as was also the objective, a 6” Unifocal Anastigmat, used at full aperture. Both performed admirably.
A second observer, or rather “ controller,’ is in charge of the exciting current, which must be carefully regulated, since too strong a field would so increase the speed as the float approaches a pole that the observer could not dot in the positions fast enough, and there would also be the danger that acceleration would not be taken up by the friction of the medium. The plate, after completion of the records for a given arrangement of poles (which may take up to eight hours), is now removed, and the dots gone over with water- proof Indian ink. A negative is now made by contact on a backed Imperial Process plate.
The variation of the intensity of the exciting current is controlled by an electrolytic resistance; a long china dish containing a sheet of absorbent cotton wool, and well wetted with a dilute solution of sodium phosphate or copper sulphate. The movable electrode is a small block of lead with a short string hanging down, which serves to reduce the current to a minimum without breaking it when the block is raised off the wet cotton.
An ammeter reading to 1/100ths is interposed, for though the motions of the float are the main guide to the controller of the current, the indications of the ammeter enable him after a little while to prevent instead of correcting variations of speed. ‘The source of energy is from the town supply, D.C.,
230 v.; the maximum current used about 6 amps., the minimum about ‘02. F2
36 Scientific Proceedings, Royal Dublin Society.
It soon became evident that the method was susceptible of great accuracy, and is yet capable of further improvement; but we content ourselves with indicating the lines along which we worked, as the results obtained were sufficient for our purpose, leaving other refinements to those who may be induced to pursue the matter further with a view to obtain
quantitative results.
"* No 3
S——> NN
Fie. 1.
Errors of the Method.
We have already referred to surface-tension and its practical elimination However, floating dust, bubbles, &c., deviate the path of the float, and must be avoided. Their effect is easily seen by the recorder, and when observed he effaces the curve commenced, and repeats the record after the controller has skimmed the peccant particle away.
Fig. 1 shows the trajectories of the paraffin sphere, when started from various points in the field of two unlike magnetic poles, which were reversed with respect to the horizontal field of the earth’s magnetism. The figure bears a striking similarity to the well-known distribution of lines of force for leke poles.
The cross + marks the point equidistant from either pole-piece, and will be referred to as the Centre of the Field or C.F. The © marks the spot where the sphere remains at rest. For a small displacement along the diameter this is a position of stable equilibrium, but for a displacement
Breras anp Harroe—Path of a Small Permeable Body, &c. 37
along the axis it is a position of unstable equilibrium, the sphere moving to the nearer pole.
We refer to this spot as the Resting point or R.P. The two poles are, of course, also R. P.’s, stable for all displacements. The most noteworthy feature in this diagram is that while the curves are symmetrical about the axis, the R. P. does not coincide with the C. F., and the diameter is curved.
Fig. 2 shows the path of the same sphere in the field between two South Poles. Here there is not such a lack of symmetry. The C.F. and R.P. are practically coincident, but there are in addition two other
Fie. 2.
“diametral” R.P.’s with a change in the sign of the curvature of the trajectories on either side. Thus there are in this field five R. P.’s, viz. the two poles stable for all displacements, the C.F. unstable for all displace- ments, and the two new ones which are stable for displacements along the diameter only, but unstable for all others, the particle moving along a curve to one or other pole. The actual position of the diametral Resting Points of an inductor depends on the theory of greatest diameters.
Fig. 3 shows the trajectories of the same sphere in the extra-polar regions of the fields shown in fig. 1, and fig. 4 a similar region corresponding to fig. 2.
The lines are practically radial near the poles, and, beyond indicating some changes of curvature in the outer regions, show little of interest. We
38 Scientific Proceedings, Royal Dublin Society.
include them merely to show that the extra-polar field was not overlooked ; but we concern ourselves at present with the inter-polar space. Want of Symmetry.
In our earlier investigation we were much troubled by a lack of symmetry in our diagrams. To facilitate observation, we had erected our apparatus without reference to its magnetic bearing, judging that the earth’s field would not appreciably interfere with the strong electro-magnetic field. We were speedily undeceived, however, as in the outer and weak parts of the field distortion was considerable. On swinging the magnet so that its axis lay north and south, matters were improved, but distortion was still present.
Fie. 3.
We found that the base-plate of our magnet was of rough cast-iron considerably harder than the wrought-iron cores, and having been once magnetized retained that magnetism with remarkable tenacity. Reversing the current in the coils of the magnet only produced a temporary reversal of the lines in the sole, which assumed its original magnetic state when the current was broken. It was evident then that a certain minimum of current was required to magnetize the sole in a contrary direction to its permanent magnetism. Now, as we were accustomed to regulate the strength of our field by varying the current between °6 and 02 amps., at a
Beas and Hartoe—Path of a Small Permeable Body, &c. 39
certain stage the sole, freed from this coercive force, would suddenly reverse, and we would now be working in a highly complex field, viz., (i) the earth’s horizontal component ; (ii) the field of the electro-magnet parallel indeed to this; (iii) the sub-permanent field of the sole, whose poles might be any- where in it. We took off the sole, had it heated red-hot and cooled all night in cinders lying east and west; but even this failed to quite remove the permanent magnetism, although the curves were somewhat amended. We now abandoned the base-plate, supported the magnet poles on a wooden base, and removed then to a small room set apart for magnet work, being free from iron fixtures.
Fie. 4.
On repeating our work, there seemed at first to be a marked improvement, but sooner or later a curve would be traced which would cross some of the previous ones, and the stage at which this interesting event would take place could not be foretold.
It seemed to us that though we had no permanent magnetism cropping up as before, yet as the two cores of the magnet were unlikely to be exactly alike in hardness, we were dealing with two separate magnets of unequal strength, and moreover, the ampere-turns on each were not likely to be exactly the same; the case was even worse than before; so we returned to the base-plate, taking care that its permanent magnetism was in the same
40 Scientific Proceedings, Royal Dublin Society.
direction as the electro-magnetism of the cores, and not reversing the current at any time during the taking of a set of records.
Thus we obtained curves which, though possessing but a bi-lateral symmetry about the interpolar axis, are not otherwise distorted.
The curvature of the diameter and non-coincidence of the R. P. and C.F. are due to the combined effects of the magnetism of the sole, and the earth’s horizontal field—but it is beyond the scope of this paper to analyse these effects singly.
The latter might be eliminated entirely by working in a closed chamber with thick walls of soft iron. Effects due to permanent magnetism of the iron might be eliminated by making the electro-magnet of laminated Swedish charcoal iron throughout.
In presenting our results we lay stress on the following points :—
(i) The path of the body depends upon its size.
(ii) The field in which it moves is not constant. Itis, in fact, the resultant of the earth’s field and a parallel field, whcih is varied in intensity for reasons already shown.
(iii) The presence of the ebedy. modifies the geometrical configuration of the field.
We realize that there are serious objections to be overcome in order to obtain quantitative results, and that the curves we show are the paths of one particular body moving in one particular resultant field; but we consider that such results are a first approximation to the experimental solution of a difficult problem.
This investigation was napdle to supply the approximate physical data demanded for biological phenomena by one of the authors; and has supplied to him what was needed. As his collaboration now ends, we must apologize
for presenting a research in a state which may be critized as inchoate by the professed physicist.
Nore.—During the interval that elapsed between the reading of this paper and its publication, Dr. Felix E. Hackett (Royal College of Science, Dublin) has pointed out from theory that in the horizontal plane through the poles VN’ there is a maximum for the magnetic force along the perpendicular bisecting WV’ at O, at a point P, such that OP = ON x “708; and hence P is a rest point. This is not in accordance with the results of our experiments, and I hope shortly to investigate the discrepancy. Professor Bergin, M.a. (University College, Cork), also mentioned this, and showed that there are other maxima along lines prallel to OP. These would not be found by our method of experiment ; but might be shown if the particle were constrained to move (say) in perfectly smooth glass tubes. These maxima soon disappear as either pole is approached.—P. E. B.
SCIENT. PROC. R. DUBL. SOC., N.S., Vou. XV. PLATE I.
CAMERA AND OTHER APPARATUS USED IN THE EXPERIMENTS (vide p. 35).
SCIENTIFIC PROCEEDINGS.
VOLUME XV.
1. The Subsidence of Torsional Oscillations and the Fatigue of Iron Wires when subjected to the Influence of Alternating Magnetic Fields of Frequencies up to 250 per second. By Wittram Brown, 8.sc. (January, 1916.) 6d.
2. Preliminary Notes on the Carbohydrates of the Musci. By Tuomas G. Mason, 8.4., Dipnom. Acric. (February, 1916.) 64d.
8. A New Form of very High Resistance for use with Hlectrometers. By Joun J. Dowtine, M.a., M.R.LA. (February, 1916.) 6d.
4, On the Path of a small Permeable Body moving with Negligible Acceleration in a Bipolar Field. By Purmir H. Banas, B.a., a.R.c.sc.1., and Marcus Harroe, M.A., D.sc. (N.u.1.) (Plate I.) (February, 1916.) 6d.
DUBLIN: PRINTE]) AT THK UNIVERSITY PRESS BY PONSONBY AND GIBKS.
THE
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Vol. XV. (N.S.), No. 5. FEBRUARY, 1916.
THE CHANGE OF LENGTH IN NICKEL WIRES OF DIFFERENT RIGIDITIES, DUE TO ALTER-
NATING MAGNETIC FIELDS OF FREQUENCIES UP TO 150 PER SECOND.
BY
WILLIAM BROWN, B.Sc.,
PROFESSOR OF APPLIED PHYSICS, ROYAL COLLEGE OF SCIENCE FOR IRELAND, DUBLIN [Authors alone are responsible for all opinions expressed in their Communications. |
DUBLIN: PUBLISHED BY THE ROYAL DUBLIN SOCIETY LEINSTER HOUSE, DUBLIN. WILLIAMS AND NORGATE, 14, HENRIETTA STREET, COVENT GARDEN, LONDON, W.C
Va 1916.
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Authors desiring to read Papers before the Society are requested to forward their Communications to the Registrar of the Royal Dublin Society at least ten days prior to each Meeting, as no Paper can be set down for reading until examined and approved by the Science
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es
V.
THE CHANGE OF LENGTH IN NICKEL WIRES OF DIFFERENT RIGIDITIES, DUE TO ALTERNATING MAGNETIC FIELDS OF
FREQUENCIES UP TO 150 PER SECOND.
By WILLIAM BROWN, B.Sc., Professor of Applied Physics, Royal College of Science for Ireland, Dublin.
{Read DecempeER 21,1915. Published FEBRuARy 28, 1916.]
EaRLy in the year 1914 the present writer brought before this society the results of some experiments on the change in the length of a soft nickel wire when it was subjected to the influence of alternating magnetic fields of frequency 50 per second.
The present communication gives results obtained with nickel wires in jiwe different states of rigidity, when they were subjected to the influence of longitudinal magnetic fields, direct and alternating up to a frequency of 150 per second.
The rigidity of each wire was measured by means of a slightly modified form of Searle’s torsion apparatus already explained in a previous paper by the writer.” In the case of each wire employed the length was 226 cms. and the diameter 0:169 cm., and the magnetic field was in every case uniform throughout the entire length of the wire. The longitudinal loads used were in the ratio 1, 4, 16, the greatest load being 2 x 10° grammes per sq. cm.
The change in the length of the wire when the magnetic field was applied was read off directly by means of a microscope reading to 9:2 x 107 per unit length of the wire, as already explained in the author’s former paper.’
The temperature of the room during the experiments was kept as nearly as possible at 17°C.
It was found that when a direct magnetic field was started round the wire, and during the application of an alternating magnetic field, that the wire became slightly heated, as shown by the slight elongation observed by
1Scient. Proc. Roy. Dub. Soc., vol. xiv, No. 21. 2 Scient. Proc. Roy. Dub. Soc., vol. xii, No. 36, p. 481. 3Scient. Proc. Roy. Dub. Soc., vol. xiv, No. 21, p. 298. SOIENT. PROC. R.D.S., VOL. XV., NO. Y. G
42 Scientific Proceedings, Royal Dublin Society.
means of the microscope; and in order to avoid as much as possible any error due to this heating of the wire, the following method of taking the readings was adopted:—The magnetic field was put on the solenoid—and kept on as short a time as possible—and the hair in the eye-piece of the microscope set after a few trials on the given mark on the wire, then, before the second or zero reading was taken, an interval of from 2 to 12 minutes was allowed to elapse, so that the expansion by heat due to the magnetic field was avoided.
This heating of the wire by an alternating magnetic field of frequency 250 per second was so great that experiments with this magnetic field were not continued. Moreover, it was considered that the results obtained with an alternating magnetic field of frequency 150 per second indicated what might be expected from applying the higher frequency magnetic field.
In order to compare the results obtained in the case of alternating magnetic fields, with those obtained with direct magnetic fields, observations were made up to a maximum value of 200cg.s. units in both cases; the alternating magnetic fields are expressed as root-mean-square values.
The results obtained with the wire having a simple rigidity of about 810 x 10° grammes per sq. cm. are shown in Tables I, II, and IiI, when here, as well as throughout the paper, H stands for the strength of the applied magnetic field, whether longitudinal (D.C.) or alternating (A.C.), and » for the frequency of the alternating field.
TABLE I. Rigidity = 810 x 10° grammes per sq. em. Load = 0°125 x 10° .
= x 10° ems. A.C D.C.
H n= 25 n= 50 n = 160 20 4 5:5 7:5 10°5 40 8 10°8 13°8 18 60 11°5 15°5 19 23°8 80 14:5 19°5 24 28°5 120 20°5 25°8 315 35 160 25 30°5 36°8 39°5 200 29 34 40 42
Brown—The Change of Length in Nickel Wares. 43
TasLe II. Rigidity = 810 x 10° grammes per sq. cm. Load = 0°5 x 10°
” ” ” »”»
e x 10-° cms. A.C. D.C. H. n= 25 n= 50 n= 180 20 4 5 5:5 8 40 8 10 11 14-5 60 12 14 15°5 19 80 15°5 17°5 19°5 23 120 21 23 27-5 28 160 25 27 30 32 200 27-5 30 33 34 TaBLeE III. Rigidity = 810 x 10° grammes per sq. cm. Load = 2 x 10° a Sy delat ness a x 10-6 cms. Z A.C. D.C. H. n= 25 nm = 150 20 4 4°5 6°5 40 75 8°5 12 60 11 12°5 16°5 80 14 16 20 120 19 21°5 25 160 23 25 28 200 26 27°5 30
In this last Table the values corresponding to n=50 are omitted because G2
44 Scientific Proceedings, Royal Dublin Society.
for this frequency of an applied A.C. field it was found that the wire with this load on was thrown into such a state of vibration that it was impossible to take readings. The natural vibration frequency of the wire in this case was probably some harmonic of that of the applied field.
Taking the values of the contraction in Tables I, II, and III for the magnetic fields of 200 units, we find generally that, as the load on the wire is increased the contraction is decreased. When the load is increased 16 times the contraction is decreased about 10 per cent. for the longitudinal magnetic field, and about 30 per cent. for an alternating magnetic field of frequency 150 per second. For the same magnetic field of 200 units, when the frequency of the applied alternating magnetic field is increased 6 times the contraction of the wire is increased by about 24 per cent. for the light load, 13 per cent. for the middle load, and 9 per cent. for the highest load used.
In Tables IV and V are given the results obtained with a wire having a rigidity of about 708x 10° grammes per sq. cm. When the alternating magnetic fields were applied to the wire when it had the light load on, the vibrations were such that the readings on the microscope could not be taken. The values of the contraction obtained with this load, (0°125 x 10°) grammes per sq. cm. in the direct longitudinal magnetic field, are given in Table IV in the column marked d.c.
TaBle IV. Rigidity = 708 x 10° grammes per sq. cm.
Load = 0:5 x 10° grammes per sq. cm.
° x 10-6 cms. A.C duc. D.C
H. n= 25 n= 50 n= 150
20 10°65 10 11°65 14 16
40 19 18 20 24 26
60 26 24 26°5 31 34
80 31-5 28°5 31:5 86°5 39°5 120 40 35°5 38°5 45-5 48 160 45°5 40°5 43°65 52°5 5a 200 49°5 44 48 58 61
Brown—The Change of Length in Nickel Wires. 45
TABLE V.
Rigidity = 708 x 10° grammes per sq. cm.
Load = 2x 10° grammes per sq. cm.
- x 10-° cms. A.C D.C.
H n=20 n= 50 n = 150 20 ll 11:5 12 14 40 19 20 21 24 60 25 27 28 31°5 80 30 32 34 37 120 36 39 41:5 45 160 40 43°5 47 51 200 42 47 52 56
From Tables IV and V, by considering the values of the contraction obtained with the wire in this soft state, when in the magnetic field of 200 units, we find, for a longitudinal magnetic field, that when the load is increased 16 times the contraction is decreased about 15 per cent., that is half as much again as when the wire was harder.
For the same magnetic field of 200 units, when the frequency of the applied alternating magnetic field is increased 6 times, the contraction is increased about 27 per cent. for the middle load and 19 per cent. for the high load, which is about double that obtained with the hard wire, that is for a difference in the rigidity of about 123 per cent.
Three other wires having rigidities intermediate to the two already mentioned were tested in a similar manner, when they were under two different longitudinal loads, and when they were subjected to the influence of longitudinal magnetic fields, and alternating magnetic fields of frequency 150 per second only. The results so obtained are given in Tables VI, VII, and VIII, the numbers in the tables being as before the values of dl
7 x 10-* cms.
46 Scientific Proceedings, Royal Dublin Society.
TABLE VI.
Rigidity = 790 x 10° grammes per sq. cm.
Load = 0°5 x 10° grams. Load = 2 x 105 grams. per sq. cm. per sq. cm. A.C. A.C. D.C. a D.C. H. n= 150 n= 150 20 6 9°5 6 8 40 11 17 9°5 16 60 16°5 23 13°5 20 80 19 27 17 24 120 26 33 22°5 29°5 160 28°5 37 26°5 33 200 31 39 29 35 TaBLe VIL.
Rigidity = 750 x 10° grammes per sq. cm.
Load = 0°56 x 105 grams. Load = 2 x 10° grams.
per sq. ¢.m. per sq. ¢.m. NO) A.C. D.C. SS > D.C.
H. | | »=150 n = 150 20 7 15 7 9 40 13°5 26 13 17 60 19 33 17-5 23 | 80 23:5 38 | 21-5 28 120 | 30° 44-5 28 36 160 | 34:5 48 32 41 XM | Be 50 35 45
Brown—The Change of Length in Nickel Wires. 47
TaBLE VIII.
Rigidity = 715 x 10° grammes per sq. em.
Load = 0°5 x 10° grams. Load = 2 x 105 grams. per sq. cm. per sq. cm. A.C A.C D.C. —— = DC. H n= 150 n= 150 20 11 20 9 11 40 19°5 32 16°5 20 60 26 39 22°5 28 80 30 44 27 34 120 36°5 51 34 42°5 160 40°5 56 38 49 200 43 59 4] 54
The values of the contraction as affected by the rigidity, load, and magnetic field in the three wires last mentioned, will be found to lie inter- mediate to the values obtained with the wires when in the hardest and softest states.
In Table IX are collected the values of the rigidity and the values of the contraction obtained with longitudinal magnetic fields of 200 units produced by direct current and alternating current of frequency 150 per second, when the wires were under the influence of two different loads.
48 Scientific Proceedings, Royal Dublin Soczety.
TABLE IX. Load = 0°5 x 10° grams. Load = 2 x 10° grams. per sq. em. per sq. cm. Rigidity | grammes A.C. A.C. Dey eek DE =| DG n = 150 n= 150 | 810 x 106 27°5 34 26 30 LO” a 31 39 29 35 UBD 50 37 50 35 45 ; 7B 5p 43 59 41 54 OStmys 44 61 42 56
These values in Table 1X lead to a very interesting result, for if we plot the values of the rigidity of the wire as abscissae, and as ordinates, the corresponding values of the contraction produced by a magnetic field of 200 cg.s. units, we find that the points for both the direct and alternating magnetic fields lie very approximately on two straight converging lines. When the load of 0°5 x 10° grammes per sq. cm. is on the wire these two lines when produced meet at the point marked 870 x 10° on the scale of rigidity, which means that, if it were possible to have a nickel wire of rigidity 870 x 10° grammes per sq. cm., the contraction due to the action of the direct and the alternating magnetic fields of 200 units would be of the same amount. When the longitudinal load on the wire is 2 x 10° grammes per sq. cm. in the same way, the plotted results give two straight lines which when produced meet at the point marked 850 x 10° on the scale of rigidity These values are, of course, imaginary, as it is not likely that the material nickel could be put into such a physical state that its rigidity would be either of the values mentioned above.
Brown—The Change of Length in Nickel Wires. 49
Magnetic Field.
The figure shows in the form of curves the results obtained with the wires having the highest and the lowest rigidity of those used in the experiments when the longitudinal load of 0:5 x 10° grammes per sq. cm. was on the wires, and when the wires were under the influence of magnetic fields D.C. and A.C. of frequency 150 per second.
The two higher curves are those obtained with the wire having rigidity 810 x 10° grammes per sq. cm., and the two lower curves those obtained with the wire of rigidity 708 x 10° grammes per sq. cm.
From these curves, as well as from Tables II and IV, above, it will be seen that for a decrease in the rigidity of about 124 per cent. the contraction of the
SCIENT. PROC. R.D.S., VOL. XV., NO. V. H
50 Scientific Proceedings, Royal Dublin Society.
nickel wire in a magnetic field of 200 c.g.s. units is increased by about 60 per cent. for a direct field and about 80 per cent. for an alternating field of frequency 150 per second.
For assistance in reading the microscope I am indebted to Mr. A. V. Henry, a third-year Experimental Science Teacher-in-Training in this College.
SCIENTIFIC PROCEEDINGS.
VOLUME XV.
. The Subsidence of Torsional Oscillations and the Fatigue of Iron Wires when subjected to the Influence of Alternating Magnetic Fields of Frequencies up to 250 per second. By Wittiam Brown, B.sc. (January, 1916.) 6d.
2. Preliminary Notes on the Carbohydrates of the Musci. By Tuomas G.
Mason, B.A., Dirtom. Acric. (February, 1916.) 6d.
‘8. A New Form of very High Resistance for use with Electrometers. By Joun
J. Dowzine, m.a., M.R.1.A. (February, 1916.) 6d.
. On the Path of a small Permeable Body moving with Negligible Acceleration in a Bipolar Field. By Pumm H. Benas, B.a., a.R.c.sc.1., and Marcus HarroG, M.A., D.Sc. N.U.I.) (Plate I.) (February, 1916.) 6d.
. The Change of Length in Nickel Wires of Different Rigidities, due to Alternating Magnetic Fields of Frequencies up to 150 per second. By Wittram Brown, z.sc. (February, 1916.) 6d.
DUBLIN: PRINTED Al’ THE UNIVERSILTY PRESS BY PONSONBY AND GIBES.
THE
SCIENTIFIC PROCEEDINGS
OF THE
ROYAL DUBLIN SOCIETY.
Vol. XV. (N.S.), No. 6. MARGH, 1916.
OSMOTIC PRESSURES IN PLANTS.
V1I.—Own THE Composition oF THE SAP IN THE ConDUCTING Tracts oF Trees at DirrereENtT LEVELS AND AT DirFeRENT SEASONS OF THE YEAR.
BY
HENRY H. DIXON, Sc.D. (Dust), F.R.S.,
UNIVERSITY PROFESSOR OF BOTANY, TRINITY COLLEGE, DUBLIN ;
AND
W. RB. G. ATKINS, Sc.D. (Dust), F.L.C.,
ASSISTANT TO THE UNIVERSITY PROFESSOR OF BOTANY, TRINITY COLLEGE, DUBLIN.
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Rode
Wel:
OSMOTIC PRESSURES IN PLANTS.
VI.—ON THE COMPOSITION OF THE SAP IN THE CONDUCTING TRACTS OF TREES AT DIFFERENT LEVELS AND AT DIFFERENT SEASONS OF THE YEAR.
By HENRY H. DIXON, Sc.D. (DuBL.), F.R.S.,
University Professor of Botany, Trimity College, Dublin ; AND W. R. G. ATKINS, Sc.D. (DuBt.), F.I.C., Assistant to the University Professor of Botany, Trinity College, Dublin.
(Read Decemper 21, 1915. Published Marcu 21, 1916.]
IN a previous paper of this series (1) it was shown that the sap centrifuged from the wood of trees always contains sugars and salts, the former being in preponderating quantities as a rule. Furthermore, it was proved that the sugars are present during early spring in larger amounts than at other times. Certain views were also put forward regarding the functions of the living elements of the wood, and root-pressure was explained with due regard to the quantitative measurements of the osmotic pressure of the wood-sap.
In the above-mentioned research attention was mainly focussed on the constituents of the sap at constant levels in the various trees investigated. The aim of the present paper is to study the composition of the sap at different levels in the same tree, and to repeat the examination during the seasons of the year upon closely similar trees.
With this object nine trees were investigated—three of Acer mac- rophyllum growing out of one old stump, and very much alike in their dimensions; two each of Ilex aquifoliwm and Cotoneaster frigida; and one each of Arbutus wnedo and Ulmus campestris. Thus the list includes the evergreens Tlex and Arbutus, the sub-evergreen Cotoneaster frigida, and two typical deciduous trees, Acer and Ulmus. It would be preferable to include a larger variety of trees, and a greater number of each species; but up to the present we have had opportunities of investigating only a limited number.
As in former papers, A denotes the depression of freezing-point of the sap as ascertained by the thermo-electric method of cryoscopy, and P the osmotic pressure in atmospheres, calculated from A. Under C x 10° are given
SCIENT. PROC. R.D.S., VOL. XV., NO. VI. I
52 Scientific Proceedings, Royal Dublin Society.
the values of electrical conductivity measurements, expressed in mhos, upon the same sap. A, represents the depression of freezing-point occasioned by the electrolytes; this is calculated by finding the value of A for a solution of some standard substance, such as potassium chloride, which has an electrical conductivity equal to that of the sap. As explained in an earlier paper (1), this is an approximate value, but it is sufficiently accurate for dilute solutions. Accordingly, A — A, is a fairly reliable measure of the non-electrolytes, which are almost entirely sugars, dissolved in the saps under examination.
In the two columns at the right are shown the percentages of reducing sugars (R) and of sucrose (S) found. The reducing sugars include the mono-saccharides, glucose, (dextrose) and d-fructose (laevulose) and the disaccharide maltose. The latter was found only in a few instances. Its presence was detected by means of its phenylosazone, and a rough idea of the relative amounts of the two hexoses and maltose was obtained by micro- scopic examination of the osazone crystals. It must be remembered that these hexoses yield the same osazone. The percentages shown are only rough estimations carried out upon the sap by Fehling’s solution. The figures for sucrose were obtained by treating sap, inverted with hydrochloric acid, in the same manner. Allowance was of course made for the reducing sugars previously found. The figures under R are calculated as if only glucose were present; thus when maltose is present the value will be too low, as the reducing power of maltose is only about half that of glucose, weight for weight.
Deciduous Trees.
Below are recorded the results afforded by the examination of portions of the stem of a large elm, felled on March 3rd. The sap was extracted by centrifuging small cylinders of wood, as previously described (1).
TABLE I,
Ulmus campestris. Wood-sap from tree, March 4th.
| | Percentage of Sugar | Expt.} Source of Sample A A, N= LN, 12, C x 10° | Medicine | sugar _| Sucrose | caleulated jas glucose 805 | Stem, 0°6 metre level | 0°094° | 0:044° | 0-050° 1:13 95-5 0°5, m. 0-5 806 | Stem, 16 5p 0°174° | 0-059° | 0-115° 2-09 127°2 | 0°5, m. 0-8 807 | Stem, 20 a 0°293° | 0:047° | 0-246° 3°52 101°8 | 2-0, m. 1-0 1
Dixon ano AvrKkiIns—Osmotie Pressures in Plants. 53
It may be mentioned here for the sake of comparison that a—
1 per cent. solution of glucose gives a depression of 0°106°, and a i joer Cais gy >) SUCEOSE ,, ee 5) ORDEAE,
These figures indicate the values 0:08°, 0:08°, and 0:266° respectively for A — A, in the above three experiments. As may be seen from the table, the values of A - A, show that the sugar determinations are over- and under- estimates in the first two respectively, and the error in each is much the same. The third is an under-estimate, but the agreement is good. he occurrence of maltose, as well as of hexoses, is denoted by m. Microscopic examination of the osazones showed that in the first maltose and hexoses were present in roughly equal quantities; in the second the hexoses predominated, and the same was true of the third.
The table shows that the fraction of the osmotic pressure of the sap attributable to non-electrolytes is greater than that due to electrolytes, but the preponderance becomes more marked at the higher levels. As noted in the first paper (1), this demonstrates that the percentage by weight of the non-electrolytes far exceeds that of the electrolytes, for osmotic pressures are proportional to molecular concentrations, and the sugars have much higher molecular weights than have the salts of the sap. The latter, moreover, are ionised, so as to yield two or more ions, each of which functions as a molecule as far as osmotic pressure is concerned.
Furthermore, it is seen that the rise in osmotic pressure as the higher levels are reached is entirely brought about by the increase in the quantities of sugar present, not by the electrolytes. This must not be taken to mean that no other non-electrolytes are present, but only that the agreement between the values of A — A, and the results of the rough sugar estimations are such as to justify one in speaking of the sugars as the controlling factor in the total of non-electroly tes.
Comparison of the figures given by Ulmus with those of Acer recorded in this and the first paper shows that the relatively high values for the osmotic pressure and sugar content of the sap are due to the vernal mobilization of carbohydrate reserves. The presence of maltose also points to this, as it is usually absent from wood-sap at other times of the year, being probably hydrolysed to glucose in the living elements of the wood when secretion of sugar takes place at a slower rate. With regard to this secretion, or diffusion as it appears to be in reality, it may be recalled that Osterhout (2) has shown how greatly the presence of certain sugars may increase the permeability of protoplasm. In this sucrose has a more marked action than have other
sugars. 12
o4 Scientific Proceedings, Royal Dublin Society.
A particularly favourable opportunity for studying the variation in the composition of the sap, both with respect to the height above ground and to the season, was afforded by three tall stems from a large old stump of Acer macrophyllum growing in the Botanic Gardens of Trinity College, Dublin. Two of these, felled in October and February, were as similar as two trees could possibly be, and sap was obtained from them at intervals up to 10 metres. The third, felled in April, was slightly smaller, but afforded material for examination up to 9°5 metres. The results are given in Tables II-IV.
TABLE II.
Acer macroyphyllum, October 135th.
R 8 noe 5 = = IB Ox 10 ey ASB, percent. | percent. Root . 6 . | 0:060° 0°72 76°4 0:035° | 0:025° 0 0-6 Stem 0m. level . | 0°053° 0°63 84°6 0-039° | 0:014° 0 0°35 og 2h ile op 0-046° 0°56 61:0 0-028° | 0-018° 0 0°25 ny hits py 6 |) OO | Oe) 54:2 | 0:025° | 0-010° 0 0 1 Oi go | OWL? || Oe 64:8 | 0-030° | 0-010° 0 0 Bim g 0 | OWASP | way 70-9 | 0:033° | 0-015° | Trace 0-5 minute pg HDR 55 . | 0:068° 0:81 79°0 0:037° | 0:031° | Trace 0°5 minute TABLE ITI.
Acer macrophyllum, February 25th.
R 8 os 5 Re a ue O25 WO ae A= ay, percent. | percent. Root . 0 . | 0°089° 1:07 84°8 0:089° | 0:050° | Trace 10
minute Stem 0 m. level . | 0°146° 1:76 111°4 0:052° | 0:094° | Trace 1:5
Ag Pe NS ap . | 0°146° 1°76 92°4 0:048° | 0:108° | Trace 2-5
op Gh Site a9 . | 0-178° 2°14 85-0 0:039° | 0:189° | Trace 3-0 minute
99 ils 55 5 erty? 2°15 94°4 0:044° | 0-185° 0 3:0
op Hl pp on |} Wz? 2-70 71-2 0°088° | 0-191° 0 4:0
,, 10 m. ,, .| 0°307° | 3-71 | 142-6 | 0-067° | 0-240° 0 5-5
Drxon ann Arkins—Osmotic Pressures in Plants. 55
TABLE LV. Acer macrophyllum, April 14th.
| : R iS) ne 7 P | Cx 10° Ae A=By percent. | percent. : Root . é 5 || Ornitne 1°34 | 140°6 0:066° | 0:045° | Trace 0-4 | Stem 0 m. level . | 0-109° Royle a@ee) 0-051° | 0:058° | Trace 0-4 | minute py Pe EM ap - | 0-108° 1:30 108°6 0:050° | 0:058° 0 0-4 op eee on . | 0-108° 1:30 97:1 0:045° | 0:065° 0 0-5 pp Os oy . | 0°144° 1:73 117°8 0:055° | 0-089° 0 0-7 9 3 URS 5g . | 0°165° 1:98 121:9 0:057° | 0:108° 0 0-7 pp GPO) 1s 5, . | 0°180° 2°16 139°3 0:065° | 0-115° | Trace 0-7 minute
As the chief interest attaches to the values of A - A,, R, and 8, they have been recorded in Table V, the figures for the three trees at different levels being placed side by side for the sake of comparison. Graphs of the concen- trations of the non-electrolytes at different levels, and at different dates, are given in the figure on the next page.
TABLE V.
Acer macrophyllum.
A — A, (total sugars) R percentage S percentage ae ; Oct. 13 | Feb. 25 | Apl. 14| Oct.13 | Feb. 25 | Apl. 14 | Oct. 13| Feb. 25) Apl. 14 Root . 3 - | 0°025° | 0:050° | 0:045° 0 Trace Trace 06 1:0 0-4 minute Stem 0 m. level | 0°014° | 0:094° | 0:058° 0 Trace Trace 0°35 1°5 0-4 minute opp IRS! Las 0:018° | 0:108° | 0-058° 0 Trace 0 0°25 2°5 0-4 59 6 Ts 65 0:010° | 0°1389° | 0:065° 0 Trace 0 0 3°0 0°5 minute »» 6m. ,, | 0-010° | 0-135° | 0-089° 0 0 0 0 3-0 0-7 pp 3 Wo 9p 0-015° | 0:191° | 0-108° | Trace 0 0 0°56 4-0 0-7 minute pp WO) Ms Gp 0:081° | 0:240° | 0:115° | Trace 0 Trace 0-5 55 0-7 minute minute
From Tables II, III, and IV it may be seen that the osmotic pressure of the transpiration stream is greatest at the top of the stem in each case. While this is so the gradient and the absolute value vary greatly at different seasons. In the autumn the root possesses higher osmotic
56 Scientific Proceedings, Royal Dublin Society.
pressure than the lower portions of the stem, the minimum lying at the 4-metre level. In the early spring the gradient from root to summit is unbroken, and the same is true in the late spring. The greatest pressures are found in early spring.
The electrical conductivity measurements do not show such a degree of
O-A. 0:2405
0-220)
0-200
0-180)
0:160°
0-140
0-120"
0-100"
0:080
0 060)
0-040,
2 4 6 8 10 Height above ground-level in metres.
regularity as the osmotic pressures, but in a general way they follow the latter in autumn, inasmuch as the root and summit are higher than the 4-metre level, which is a minimum value. In early and late spring there is a marked rise in conductivity, the April measurements being on the whole considerably higher than those of February.
The key to the whole series of changes is, however, obtained by examining the values of A — A,, which indicate the depressions of freezing-point due to
Drxon ano ArKins— Osmotic Pressures in Plants. On
the total sugars. The sugar present in preponderating quantities is sucrose, as only traces of reducing sugars were found or none at all. For the sake of comparison these figures are recorded in columns side by side in Table V. It must be remembered that while the values of A, A, and A — A, are accurate determinations, the percentages of sugar recorded are only rough measure- ments.
It is at once evident that there is an enormous influx of sucrose in the spring, the amount being from five to fourteen times as great in February as in October at various levels in the stem. By April the quantity of sucrose has fallen to about half what it was in February.
The explanation of the rise in the sugar content, and to a lesser degree in the content of electrolytes, appears to be that the storage cells of the wood parenchyma and medullary rays are actively secreting sugar into the transpiration stream as it passes them. Consequently the latter becomes richer and richer as it ascends. It is quite possible that the secretion is really a simple diffusion of the sugar from the cell in which it is stored and formed anew by the hydrolysis of polysaccharides, into the dilute stream which is passing by.
The fact that sucrose is the most important sugar in the transpiration stream in this and many other trees cannot be passed over lightly. It is not stored as such to any very considerable extent. But starch and hemicelluloses disappear and sucrose is found. Now it is well known that diastase produces maltose from starch, and on further hydrolysis glucose results. How then does the sucrose arise? One is forced to postulate either a peculiar type of starch hydrolysis, or that the cell synthesizes sucrose from glucose as fast as the latter is formed. The subject is one for further investigation, and is allied to the production of sucrose from polysaccharides in many fruits in the last stages of ripening.
TABLE VI.
Ulmus campestris, March 38rd.
R )
| =. S E Ges ne a2 | ne percent. | percert. I i
Stem 0°6 m. level . | 0°094° 1:13 95°5 0:044° | 0:050° | 0°5 m. 0°65
op 0 || Mole 2°09 127-2 0:059° | 0°115° | 0-5 m. 0°5
59 | 0 || @opasey? 3°52 101°8 0:047° | 0°246° | 2:0 m. 1:0
In this experiment a tall tree was examined when at the stage of vernal mobilization of carbohydrates. The osmotic pressure rises very markedly
58 Seventific Proceedings, Royal Dublin Society.
towards the upper end of the stem. Unlike Acer, Ulmus possesses noticeable quantities of reducing sugars. From inspection of the phenylosazones it was seen that in the lowest portion maltose and hexoses were present in roughly equal quantities. At the 16-metre level the hexoses were in slight excess, and this excess became greater in the highest portion.
Sub-Hvergreens.
Two similar specimens of Cotoneaster, grown in a very sheltered, over- shadowed position, were examined in February and June, from the root up to the 6-metre level. In addition two others were examined in October and December, but in these latter measurements on the intervening tracts of the stem were not made.
TABLE VII.
Cotoneaster frigida, osmotic pressure in atmospheres.
— | Oct. 1914. | Dec. 1914. | Feb. 9th, 1915. June 21st, 1915. Rooth é ; 0-78 0°48 0°63 1°34 Stem 6 m. level, . 1:04 0°64 0°64 0°76
From these it is seen that the pressures are higher in October and in June than in the winter or spring, for in evergreens there is no marked mobilization of reserves in the spring. The values of the conductivity, etc., for the 1914 experiments have been published already (1). Below are given the full set of measurements for the two 1915 experiments.
TaBLe VIII. Cotoneaster frigida, February 9th, 1915.
R 8 = 5 % = P. Cx 10 Le B= Ao per cent. | percent. E ira = Root . 6 - | 0:052° 0-63 | 48°4 9:022° | 0-030° 0 0°25 Stem 0m. level . | 0:056° 0°67 87°1 0:017° | 0-039° 0°5 () 55 UbainS s 5, - | 0°042° 0°51 | 34:9 0:016° | 0-026° 0% 0- op | Zh itly op - | 0:044° 0°53 30°0 0-014° | 0:080° 0°5 0-5 a OT gn . | 0°034° 0-41 30°5 0:014° | 0:020° 0 0°65 » 4m. ,, .| 0:032° |’ 0:38 | 927-6 | 0-013° | o-019° | 0 0°5 Bile o5 = | ORO? |) Oxa0 30:7 | 0:014° | 0-036° eee 0°5 » 6m. ,, | 0:053° | 0-64 | 31-3 | 0-014° | 0-0a9° | 0 0°5 |
Dixon anp Arxkins—Osmotic Pressures in Plants. 59
TABLE IX.
Cotoneaster frigida, June 21st, 1915.
R S en? 5 = a P. Cx) 10 Bp Ay percent. | percent,
Root . a 6 |) Mai 1°34 108°9 0-051° | 0-060° 0 0°75 Stem 0 m. level . | 0:069° 0°83 67:71 0:026° | 0:048° 0°75 0°25 op db Ts 69 . | 0°049° 0°59 50°9 0:024° | 0:025° 0:5 0°25
op PT gy | OPOBE? 0-71 53°8 0:025° | 0:038° 0:5 0°5 Bills oy 6 | MOORS || OGL 48-7 | 0:023° | 0:028° | 0 0°75
ap Sb 55 . | 0-051° 0°61 48-1 0-022° | 0-029° 0 0°5 5» 5m. ,, . |-0:052° | 0-63 48-4 | 0-022° | 0:030° | 0 0-75 » 6m. , «| 0:063° | 0-76 58-0 | 0-027° | 0-036° | 2t¢® | 9-75
minute.
Perhaps the most striking fact brought out by Tables VIII and IX is the peculiar distribution of sugars in the stem-sap. Sucrose is invariably present, the quantities found in June being on the whole decidedly greater than in February. Reducing sugars, hexoses, on the other hand, are in each case absent from the root and higher portions of the stem except for traces in two instances. Yet from the ground-level up to a height of two metres about one-half per cent. is found both in spring and summer. Why a sugar should be present in quantity in one part of an ascending stream and absent in the parts below and above is a subject pressingly calling for investigation.
As compared with Acer and Ulmus the electrolyte content of Cotoneaster is low throughout the whole year. Possibly the vernal rise in electrolytes which occurs in deciduous trees is connected with the escape of organic acids and salts from the cells along with sugar.
Variations in the electrolyte concentration at different levels may be more or less explained by the action of cells adjoining the transpiration stream in abstracting materials for the growth of the cambium, &c., and by the concentration effected by evaporation taking place in the leaves. In several instances there appears a greater concentration of electrolytes at the base of the stem than in the roots. This seems to necessitate a passage of electrolytes from the cells of the wood into the transpiration stream.
SCIENT. PROC. R.D.S., VOL. XV., NO. VI. K
60 Scientific Proceedings, Royal Dublin Society.
Hvergreens.
A specimen of Arbutus was examined in December, the root, stem, and leaves being all tested. The high sugar content of the root is noticeable. Comparison of the transpiration sap with that from the leaf tissues pressed after treatment with liquid air shows how relatively enormous are the concentrations of both sugars and electrolytes in the latter. The values are given in Table X.
TABLE X.
Arbutus unedo, December 11th.
R S ae 5 | = a | Ps | osu & mC percent. | percent. Root . 9 . | 0°041° 0-50 34°2 0°016° | 0:025° 0:25 10 | Stem . : . | 0°038° 0°46 27:8 0:018° | 0:025° 0:25 0:25 Leaves . 9 . | 1:228° | 14:78 643-0 0°310° | 0:918° — -~
Two specimens of Ilex were cut down, one in the end of January after a fall of snow, and the other in March. As in Cotoneaster and Arbutus, the * conductivity of the sap is low. Again, the sugar content of the root is high. Moreover in Ilex reducing sugars are of importance throughout the whole of the conducting tracts, and are present in greater quantities than sucrose in all levels above that of the ground. The results are shown in Tables XI and XII. As in other evergreens, no vernal mobilization of reserves is to be found. The top of the stem may have a higher osmotic pressure than the lower portions and root, though in one case (as in Arbutus) that of the root was slightly greater than that of the stem.
TABLE XI.
Llex aquifolium, January 25rd.
{Fas ih ata S = 5 = | = | Ee | O20 ae A=Bs percent. | percent. Roots 5 . | 0°070° 0°84 84-7 0:039° | 0-031° — — Stem : . | 0-056° 0°67 5d°4 0:026° | 0-080° — =
Drxon anp Arkins—Osmotie Pressures in Plants. 61
TABLE XII.
Tlex aquifoluwm, March 22nd.
|
re S Fo Oe Me | Bo race Hees eee Roots vocses! ores | 46-5 | 0-022° | o-o26° | 0-25 | 0:6 Stem 0m. level . | 0-074° | 0:89 | 96:6 | 0-045° | 0-029° | 0-25 | 0-6 Im. 4, «| 0-062 | 0-75 | 71-3 | 0-083° | 0-029° | 0-25 | 0-25 » 2m. ,, .|0-066° | 0:79 | 66-9 | 0-031° | 0:035° | 0-25 | 0:25 » Bis 4 0 | OOGP — OGD | 74-6 | 0-035° | 0-032° | 0:25 | 0-25 » 4m. ,, | 0105? | 1:26 | 69:7 |\0-028° | 0-077? | 0-25 | 0-0
While obtaining the sap for these determinations one could not help being struck by the surprising amount which may often be extracted from fresh wood by centrifuging; thus the wood of Salix babylonica cut in December gave as much as 4¢.c. from a cylinder about 2 cm. diam. and 10cm. long; and a similar piece of the root of Cotoneaster frigida yielded almost as much in the month of February. A yield of 1 — 25 cc. was the usual quantity from pieces of wood of this size. Similar cylinders (viz. 2 cm. diam., 10 em. long) of lex aquifolium seldom yielded as much as 1 c.c.
The differences in the colour of the sap are also remarkable; some are pale brown, eg. that from Acer macrophyllum, A. pseudoplatanus, Populus alba, Cotoneaster frigida, and Ilex aquifolium (the last often inclines to grey) ; others, eg. from Fagus silvatica and Salix babylonica, are of a wonderfully beautiful amethystine hue. The presence of oxidases is often indicated by the darkening of the sap on exposure to air. It is open to question how far these pigments and oxidases are derived from the injured cells of the wood centrifuged, and how far they are to be regarded as part of the constituents of the transpiration stream in the uninjured stems.
SUMMARY.
1. Large quantities of sap may, as a rule, be centrifuged from the conducting wood of trees. his sap varies in colour and in electrolyte and non-electrolyte content.
2. When in a condition of physiological rest during the late autumn and winter, the osmotic pressure of the wood-sap of deciduous trees is small and approximately constant throughout; the stems, the roots, and upper portions
62 Scientific Proceedings, Royal Dublin Society.
_of the stem have, however, slightly greater pressure than the intervening portions.
3. During the early spring the sap is enriched by the addition of large quantities of sugars from the storage cells of the wood-parenchyma and of the medullary rays. Accordingly the osmotic pressure rises in a very marked degree from root to summit, the increase being particularly great in the upper regions.
4, During the late spring the concentration of sugars is still considerable, being roughly half of the earlier value. The electrolytes of the sap are, however, present in much greater concentration than in the early spring.
5. In Acer macrophyllwm reducing sugars are never found in the wood- sap, except in traces, whereas sucrose is present in quantity. In the other trees examined both reducing sugars and sucrose are present, the latter predominating as a rule. During the vernal mobilization of reserves the reducing sugars consist of the hexoses and maltose ; at other times the latter is absent.
6. In evergreens and sub-evergreens the seasonal changes are not very striking, nor are the gradients of osmotic pressures from root to summit as regular as in deciduous trees. The osmotic pressure of the transpiration sap in the root exceeds that in the stem at certain seasons.
BIBLIOGRAPHY.
1. Drxon, H. H., and Atkins, W. R. G.—Osmotic Pressures in Plants: Iv. On the Constituents and Concentration of the Sap injthe Conducting Tracts, and on the Circulation of Carbohydrates in Plants. Sci. Proce. Roy. Dub. Soe., 1915, vol. xiv (N.S.), pp. 374-392.
2. OstERHOUT, W. J. V.—Some Quantitative Researches on the Permeability of Plant Cells. Plant World, 1913, vol. xvi, pp. 129-144.
SCIENTIFIC PROCEEDINGS.
VOLUME XV.
. The Subsidence of Torsional Oscillations and the Fatigue of Iron Wires when subjected to the Influence of Alternating Magnetic Fields of Frequencies up to 250 per second. By Wintiam Brown, B.sc. (January, 1916.) 6d.
. Preliminary Notes, on the Carbohydrates of the Musci. By Tuomas G. Mason, 8.a., Direnom. Acric. (February, 1916.) 6d.
. A New Form of very High Resistance for use with Electrometers. By Joun J. Downine, u.a., u.R.1.A, (February, 1916.) 6d.
. On the Path of a small Permeable Body moving with Negligible Acceleration in a Bipolar Field. By Pamir EH. Bernas, B.a., a.R.c.sc.1., and Marcus Harroe, M.A., D.SC. N.U.I.) (Plate I.) (February, 1916.) 6d.
. The Change of Length in Nickel Wires of Different Rigidities, due to Alternating Magnetic Fields of Frequencies up to 150 per second. By Witt1am Brown, s.sc. (February, 1916.) 6d.
. Osmotic Pressures in Plants. WI—On the Composition of the Sap in the Conducting Tracts of Trees at Different Levels and at Different Seasons of the Year. By Henry H. Drxon, sc.p., (pust.), F.R.s.; and W. R. G. Arxins, SC.D. (DuBL.), F.1.c. (March, 1916.) 6d.
. The Verticillium Disease of the Potato. By Grorcn H. PeranysripGn, PH.D., B.sc. (Plates II-III.) (March, 1916.) 1s. 6d.
DUBLIN: PRINTED Al THE UNIVERSITY PRESS BY PONSONBY AND GIBBS.
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SCIENTIFIC PROCEEDINGS
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ROYAL DUBLIN SOCIETY.
Vol. XV. (N.8.), No. 7. MARCH, 1916.
THE VERTICILLIUM DISEASE OF THE POTATO.
BY
GEORGE H. PETHYBRIDGE, Pu.D., B.Sc.,
ECONOMIC BOTANIST TO THE DEPARTMENT OF AGRICULTURE AND TECHNICAL INSTRUCTION FOR IRELAND.
/ansonian Ing ow ; (PLATES II-III.) bse wip NC My. NG? Onan a] Muse8™ [Authors alone are responsible for all opinions expressed in their Communieatisne | =e DUBLIN:
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WAnl,
THE VERTICILLIUM DISEASE OF THE POTATO.
By GEORGE H. PETHYBRIDGEH, Pu.D., B.Sc.,
Economic Botanist to the Department of Agriculture and Technical Instruction for Ireland.
(Piates II-III.) {Read DecrempBer 21, 1915. Published Marcu 22, 1916.]
I. Inrropuctory.
Durine the past seven summers special investigations dealing with various diseases of the potato have been pursued in Ireland, where the potato crop is such an important one. Some of the diseases dealt with have been new, while others, although not new, were more or less obscure and had previously been insufficiently studied, so that it was possible to throw new light on them.
The results of these investigations have been published annually in the form of general summaries or reports, and in certain cases the diseases have formed the subjects of special scientific papers.’
The disease with which the present paper deals has been referred to briefly in these reports from 1910 onwards, but no detailed account of it has yet been given. It is not really a new disease, although up to the time of starting the present investigations comparatively little was known about it, and definite record of its presence in the British Isles had apparently not been made. It has, in fact, long remained incompletely studied and concealed amongst the congeries of diseases passing under the names of Curl and Leaf- Roll, from which, however, it must now be removed and be recognized as a distinct disease of a definite type caused by a specific parasitic organism, as will be clear from the discussion in Section VIII of this paper.
The reason why the present study of the disease has been a somewhat protracted one is partly because the disease was only one of several which
1 These reports will be found in the Journal of the Department of Agriculture and Technical Instruction for Ireland, vols. x, xi, xii, xiii, xiv, and xv, 1910 to 1915. References to the special scientific papers mentioned will be found in these reports.
SCIENT. PROC. R.D.S., VOL. XV, NO. VII. L
64 Scientific Proceedings, Royal Dublin Soctety.
were being studied simultaneously, but more especially because it was found that in order to obtain accurate information upon the extent and mode of transmission of the disease by affected plants to their progeny it was necessary to extend the observations over several successive seasons. Failure to do this by earlier workers has resulted in somewhat incorrect notions regarding the disease.
IJ. SympromMs AND CAUSE OF THE DISEASE.
The case of the disease which formed the starting-point of the present investigations was met with on a farm in Co. Dublin in the first week of August, 1909. The plants were of the variety Duchess of Cornwall (a type of Up to Date), and were being grown in a small plot.
The affected plants, which were distributed promiscuously through the plot, were of fair size, certainly not dwarfs, but not so large as their healthy neighbours. They were clearly distinguished from the healthy plants by the fact that their lower leaves were brown, shrivelled, and practically dead. The upper, younger internodes of the stalks had failed to elongate normally, and the leaves borne on them were more or less crowded together, forming a kind of rosette. The individual leaflets of these upper leaves were folded upwards and inwards on their midribs, consequently exposing their lghter-coloured under-surfaces to view.
On cutting the stalks transversely, the wood of three principal vascular bundles was seen to be discoloured, being of a yellowish brown tint and not so dark as is usually the case in attacks of Black Stalk Rot due to Bacillus melanogenes. On pulling the stalks from the ground, it was at once clear that the disease was not Black Stalk Rot, because the portions of them near the surface of the ground and below it were not black and rotten, but, externally at any rate, apparently quite healthy.
The parent tubers from which the diseased plants had sprung were, in the cases examined in detail, already rotten ; but it may be stated here that such tubers do not always decay in this manner, for very often they may be found, at the close of the season, hard and apparently sound.
Amongst the newly formed tubers rather small-sized ones predominated, although afew quite large ones were sometimes also present. The total yield from the diseased plants was considerably less than that from the neighbouring healthy ones. The tubers produced by the affected plants showed no external signs of any disease. When, however, these tubers were cut across at their heel (proximal) ends, most of them showed a brown, dis- coloured vascular ring, due, as subsequent microscopical examination showed, to the browning of the walls of the elements of the wood, and, in the region
Peraysripgz—The Verticillium Disease of the Potato. 65
quite close to the point of attachment of the rhizome, to discolouration of the walls of other cells also. (See fig. 7, Plate III.) This browning of the vascular ring could be seen with the naked eye, extending in some cases for quite a considerable distance towards the rose (distal) end of the tuber, and, with the microscope, it was still to be seen in sections of the vascular tissue made at the extreme rose end.
Transverse sections of the stalks of affected plants, made both in their over- and underground portions, and examined with the microscope, showed that the wood vessels were more or less thoroughly choked with branched, septate fungus mycelium which, in a rare instance or two, bore single-celled oval conidia within the cavities of the vessels. Similar mycelium was found in abundance in the wood vessels of the leaves, roots, and rhizomes of affected plants. From the rhizomes the mycelium was definitely traced into the wood vessels of the new tubers, and in one case, which will be described in detail later, it was followed by means of hand sections to a distance of four centimetres from the heel end of the tuber.
When cut portions of the affected plants (including tubers) were kept moist for a few days in covered dishes, the fungus grew out from the wood vessels and formed aerial, verticillately branched conidiophores, on the tip of each of which a glistening, spherical globule, containing a number of conidia, was borne. (See figs. 5 and 6, Plate III.)
When portions of affected stalks were allowed to remain for about twelve days under such conditions, they began to rot; and microscopical examina- tion showed that the mycelium had spread from the vessels to the surrounding tissues, was turning black, and assuming a resting condition. (See fig. 4, Plate III.)
The fungus, which infection experiments have proved to be the cause of the disease, was identified as Verticilliwm albo-atrwm, a species first described by Reinke and Berthold' in 1879, and assigned by them as the cause of a potato disease, which they regarded as Curl (Krauselkrankheit).
The appearances described above are quite characteristic of the Verti- cillium disease. A study of it, however, over several seasons has shown that its external symptoms are subject to considerable variation in intensity. For instance, the curling or rolling of the leaflets has been found to be not an absolutely constant feature of the disease, and thus the terms “Curl” and “Leaf Roll” are to be avoided in speaking of this disease, the more so since they have been used in the past in a somewhat indiscriminate way, as will be seen from the discussion in a later section of this paper.
1 Reinke, J., and G. Berthold, Die Zersetzung der Kartoffel durch Pilze. (Dritter Abschnitt. Die Kriiuselkrankheit der Kartoffel.) Berlin, 1879, p. 67. L2
66 Scientific Proceedings, Royal Dublin Soctety.
The view of the nature of the disease which has resulted from a study of it during several seasons is that it consists primarily of a more or less prema- ture death of the plant owing to a gradual process of desiccation, proceeding from below upwards. It is to be regarded as a type of wilt-disease, although actual wilting of the foliage—z.e, a condition of flaccidity, limpness, or loss of turgor in the leaves while still green—is extremely rare in this country, and has only been seen in cases where healthy plants have been artificially inoculated through wounds with pure cultures of the fungus.
In cases of severe attack the affected plants may attain the height of only a few inches, and they may be killed off comparatively early and without developing any curl or roll in the foliage. On the other hand, in cases of very slight attack the plants may attain practically their normal size, and may not begin to die off much before the usual time. Rolling or curling of the foliage may here also be absent, and such cases of the disease are easily overlooked, particularly if the plants are at the same time attacked by blight (Phytophthora wfestans) or by the Botrytis disease. Of course, the greater number of cases of the disease lie between these two extremes.
In many cases after the death of the plants black streaks are noticeable on the dead stalks. These are due to the production of the black form of mycelium by the fungus and must not be confounded with the black, adherent, flattened sclerotia of Botrytis so often seen on dead potato stalks.
The only certain means of diagnosing the disease is by finding the mycelium of Vertccilliwm albo-atrum in the wood vessels of the plant or of the tuber from which it is derived. Even the absence of the mycelium from the wood vessels of the stem, root, &c., of a plant at a given moment is not necessarily proof that such plant is not diseased, or at any rate that it will not become so. For in many cases it has been found that the mycelium passes from the parent tuber into the stalk rather slowly, and the foliage may be just beginning to show typical symptoms of the disease before the mycelium has reached the stem. The non-realization of this possibility has doubtless been the cause of some at least of the contradictory statements made with regard to this disease.
Finally, it may be stated that no case of the disease has been met with in which the affected plant has failed to bear some new tubers; and since a large proportion of these tubers contain the fungus within them, the disease will spread to the next generation. The disease, therefore, is not extinguished automatically in any given generation of affected plants, as has been supposed.
III. Previous INVESTIGATION OF THE DISEASE.
As mentioned above, Reinke and Berthold in 1879 described the disease due to Verticilliwn albo-atrum under the name of Curl-Disease
Peruypringp— The Verticillium Disease of the Potato. 67
(Krauselkrankheit). When the present investigation was started, the account given by these authors was practically the only one dealing in detail with the Verticillium disease; and although during its progress some additional information concerning it has been published, such as that by Spieckermann and by Orton, which will be considered later on, yet Reinke and Berthold’s work still remains the fundamental one on this disease. Before proceeding further, therefore, it will be necessary to give a brief résumé of the account of the disease as given by these authors, laying stress on those points which seemed to require further investigation before being accepted as conclusively established.
Reinke and Berthold describe the disease as making its appearance under three distinct forms or types (A, B, and C). Type A is seen towards the beginning of July, and is characterized by the wilting, drying up, and yellowing of the lower leaves, not accompanied, at least to any extent, by curling of the leaflets, or by brown spotting of the foliage. Fungus mycelium is present in the wood vessels situated in all parts of the plant. It is found in the new tubers, but is said never to proceed far into them, a distance of fifteen millimetres from the heel bemg the maximum observed. It is stated to pass the winter at the point of detachment of the tuber from its rhizome and partially within the tuber.
Type B of the disease is seen at the same time as type A. Some time after the middle of July, potato-stalks, which up to that time had appeared perfectly healthy, begin to show a curling of the leaflets at their edges, and brown spots begin to appear on the foliage. At length such spotted leaves become completely dried up. The tissues of all the overground portions of the affected stalks are completely free from fungus mycelium, but in the cortex of those portions of them situated below ground and in that, of the roots it is stated that Verticilliwm albo-atrwm is present. The fungus in this case also reaches the new tubers, but by exactly what route is not clear from the description. It is said to pass the winter as in the previous type at the very heel-end of the tuber, and it could never be traced any distance into the interior of the tuber.
Although the two types mentioned are generally well marked and were described separately, the authors admit that they occur not infrequently on different stalks of one and the same plant, and even sometimes on one and the same stalk. It is also admitted that in certain cases of type B of the disease, mycelium was found after a time in the vessels of the stalks. It may be stated at once that in the present author’s opinion mycelium would probably always have been found in the wood vessels of all parts of plants affected with type B of the disease had the search for it not been made too early. Types A and B
68 Scientific Proceedings, Royal Dublin Society.
of the disease then would appear to be essentially similar, the principal difference being that in type B the mycelium of the fungus takes somewhat longer to reach the plant from the parent tuber than is the case with type A.
Type C is stated to arise exclusively when tubers derived from plants affected with either type A or type B of the disease are planted, although such tubers may also give rise to “ misses,” @.e., may produce no plants at all. Plants affected with type C of the disease come above ground late, develop slowly, and remain small. The leaves do not expand fully, and are not of the normal green colour. The leaflets are curled and wavy, the petioles being bent backwards. Death and desiccation of the plants take place from above downwards, and after the death of one stalk others may subsequently develop from the same tuber, but only to die away in their turn. The stalks are exceedingly brittle, and the plants are said to die without producing any new tubers, so that the disease exhausts itself in this, the second, generation.’ No fungus mycelium is present in the vessels of plants of type C at any time; but the mycelium of V. albo-atrum is stated to be present in the cortical tissues of the subterranean portion of the stalks. The seed-tubers producing this type of the disease, when they have not already rotted in the ground, contain no mycelium in their internal tissues ; but Verticillium is stated to be present in the cells of the skin, although it does not penetrate into the subperidermal tissues.
What strikes one as rather remarkable in Reinke and Berthold’s account of the disease is the absence of the fungus from the wood vessels in types B and CO, and, as has already been surmised, this may possibly be due to the fact that a long enough period was not allowed to elapse before the examination was made.
Much stress is laid on the point that the fungus is only present at the very heel-end of the tubers derived from plants affected with the A and B types of the disease, and that even at the end of the season when such tubers had produced plants of the C type mycelium could not be found in their interiors.
The mode of transmission of the fungus from the first generation (A and B types) to the second (C type) is, as described, a most peculiar one. It is stated that when the tubers having the mycelium strictly limited in location to their heel-ends are planted in the spring the mycelium grows around the outside of the tuber in the cork layers of the skin, and without penetrating the interior. Having in this way reached the bases of the young sprouts, it
1 Jn a postscript it is stated that in a few cases tubers from plants affected with the A type of the disease gave rise to plants of the B and not of the C type; hence it is assumed that in such cases the disease would become exhausted in the third generation.
PrraHyBrIipGE— The Verticillium Disease of the Potato. 69
finds its way into them, probably through the cortical portions of the young roots. It was certainly to be expected that since the fungus was located primarily in the vessels of the affected stalks and entered the new tubers, it would pass in through the vessels, remain in them during the winter, and pass out from them into the vessels of the new stalks in the spring; but it is quite clear that Reinke and Berthold did not admit this view.
It was particularly with a view of throwing light on this point that the present investigation was started, although it was also desired to obtain information on other phases of the disease and on the behaviour of the fungus in pure culture. The account of the fresh investigations on the disease will, therefore, now be proceeded with ; and the small amount of further literature on it, published while the investigations were proceeding, will be dealt with where necessary.
IV. LocaLizATION OF THE MycrLium IN AFFECTED TUBERS.
It is a matter of no difficulty to trace by means of suitable sections the passage of the mycelium from affected stalks through the rhizomes and into the heel-ends of the new tubers. It passes exclusively through the wood vessels. This has been studied, not merely by sections, but by suitable incubation of portions of rhizomes as well as of tubers, proving that the fungus involved was the species of Verticillium in question.
All the tubers borne by an infected plant, however, do not necessarily become infected. As a rule the fungus only reaches the older and larger tubers, while the smaller and younger ones often remain free from invasion. Here it may be stated that the tubers which do not become infected with the mycelium of the fungus produce, when planted, absolutely healthy plants, and their progeny continues to do likewise. Hence, by separating out the non-infected tubers (by the method to be described subsequently) from a mixed stock of seed-tubers derived from affected plants,and by employing them as seed-tubers, it has been possible to raise a new stock free from the disease. :
As has already been pointed out, Reinke and Berthold maintain that when the fungus reaches the heel-end of a new tuber it remains strictly localized there. Spieckermann! also states that at the time of digging, the mycelium is chiefly confined to the heel-end of the tuber,and seldom proceeds further or reaches the rose-end. He believes that during the winter resting period of the tuber the mycelium does not make any further progress, since even in spring its growth has not advanced, and the sprouts are, therefore, all viable.
1 Spieckermann, A., Beitrage zur Kenntniss der Bakterien- ring- und Blattrollkrank- heiten der Kartoffelpflanze. Jahresber. d. Ver. f. angew. Bot., viii, 1911, p. 1.
70 Scientific Proceedings, Royal Dublin Society.
This author, however, does not provide any experimental evidence in favour of his contention ; and the observations and experiments now to be described show that these views do not hold good.
In 1909 a large tuber, nearly thirteen centimetres long, borne by an affected plant, was subjected to microscopic examination by means of sections of the vascular tissues removed from it, at intervals, in such a way that the use of the tuber, or rather portions of it, as “seed” for the following season would not be interfered with. By this means the mycelium was traced definitely in the vessels of the tuber to a distance of 4 cm. from its heel-end, and the browning of the woody tissue was visible to the naked eye for a distance of about 1.5 cm. beyond this point. Owing to the comparatively small size of the vessels, and the difficulty of cutting hand-sections accurately transverse to their long axis in the rose-end region, it was not possible to demonstrate with certainty the presence of mycelium in them by this method ; but it was noted that the walls of these vessels appeared, under the microscope, distinctly browned, although this was not evident to the naked eye.
This tuber was, in the autumn, cut transversely into two portions, the cut being made some distance nearer to the rose-end than the point to which the mycelium had definitely been traced. The heel-end portion had two eyes on it, while the rose had three. In the spring of 1910 the two halves were so cut that five sets were available, each containing one eye. These sets were planted in sterilised soil, each in a separate pot. Sets 1 and 2 were from the heel-half of the tuber in which the mycelium was known to be present, while Sets 3, 4, and 5 were from the rose-half in which the presence or absence of mycelium was doubtful in the autumn. It could not, at any rate, have reached them during the winter from the heel-portion of the tuber because this had already been cut off in the autumn.
The five sets were planted towards the end of April, and all of them except No. 3 produced small plants which up to the middle of July showed no symptoms of any disease. Set No. 3 was totally destroyed by a soft- rot apparently of bacterial origin, while the plant derived from Set No. 4 was practically destroyed by an attack of caterpillars. As time progressed little or no signs of rolling were observable in the leaflets of the plants; but the lower leaves began to wither and dry up; and before the end of August all three plants were practically dead, having succumbed to a progressive desiccation proceeding from below upwards. Microscopical and cultural examination showed that the vessels of these plants were completely choked with the mycelium of Verticilliwm albo-atrwm, which was also present in the roots of the plant derived from set No. 4. In two cases (Nos. 1 and 5), in
PrruyBripGeE—The Verticillium Disease of the Potato. 71
which the old sets had not rotted, but were fairly well preserved, the fungus was found to be present in their now strongly browned woody tissues.
From this experiment it seems safe to conclude that the fungus was present in the autumn in the original tuber, not merely localized at the heel- end, but also at a distance from it at least greater than one-half of the length of the tuber.
The question of the exact location of the funeus within the tuber is an important one from the practical point of view. For, if it is strictly confined to a small area near the heel-end of the tuber in the autumn, and does not progress further during the winter, it should be possible to get rid of the disease by merely cutting off the comparatively small portions of the heel- ends of affected tubers before using them for seed. This point was, therefore, gone into in further detail.
A preliminary experiment was carried out in 1910 with tubers derived from affected plants. Small portions of the heel-ends were first cut off, in order to see whether the vascular ring was browned or not. The tubers were then divided into two groups: (a) those with no browning, hence apparently healthy; and (0) those showing browning, hence presumably diseased. The tubers in group (0) were then further subdivided. From the heel-ends of one half of them the tissues were cut away until the browning of the vascular ring was no longer visible to the naked eye, while to those of the other half nothing further was done. By this means the attempt was made to divide the tubers into the following three classes:—(1) healthy; (2) primarily diseased, but rendered healthy by cutting away the diseased tissue ; (3) diseased.
The tubers were planted under field conditions at a time when it was unfortunately impossible, owing to the pressure of other work, to devote as much attention to the behaviour of the resulting plants individually as was desirable. Further, a severe attack of blight, combined with another of the sclerotium disease, seriously interfered with the success of the experiment. Nevertheless, taking as a criterion the amount of rolling in the leaflets exhibited before these diseases gained the upper hand, it was possible to see that the plants derived from the tubers of Class 3 (diseased) were decidedly the worst, while there was not any clear difference between those derived from the tubers of Classes 1 and 2. Plants with Verticillium in the vessels of their stems were found, however, in all three classes, but such plants did not appear to predominate in one class more than in the others.
The experiment, although leaving much to be desired, showed at least that no reliance could be placed on naked-eye examination of the cut ends of tubers as a means of discriminating between those containing the fungus and
SOIENT, PROC, R,D.S., VOL. XV., NO, VII, M
72 Scientific Proceedings, Royal Dublin Society.
those free from it, and proved that the cutting away of the heel-ends of the tubers was not sufficient to eliminate the disease with certainty.
It was clear that in any further experiments on these lines it would be necessary to test individually each tuber before using it to ascertain whether it contained the fungus or not, and the method of testing was as follows :—
The tubers were first thoroughly cleaned by careful scrubbing in plenty of running water, and then dried in a clean linen towel. They were purposely not treated with any disinfectant, lest some of it should be absorbed into the wound at the heel-end of the tuber caused by its severance from the rhizome, which might prevent the development of the fungus if present.
A small portion of the heel-end of the tuber, about a millimetre or so thick, was then cut in such a way that it remained hanging from the tuber by a small bit of skin, the two cut surfaces being of course exposed. Tubers prepared in this way were put into clean covered glass dishes the bottoms of which were lined with moist filter paper. After standing for two or three days at room temperature microscopic examination of the tubers was made.
Verticillium when present in the wood vessels of a tuber does not produce aerial growth and conidiophores at the cut surfaces with the luxuriance generally observed when pieces of affected stalks, rhizomes, or roots are suitably incubated. Nevertheless it does grow out in varying degrees, if present, and by microscopical examination one can decide whether a tuber possesses it or is free from it, although cases do arise occasionally where definite decision is not possible.
Examination was always carried out at three places—(1) the natural wound at the heel-end; (2) the cut ends of the vascular tissue of the small portion of the tuber nearly severed ; (3) the cut ends of the vascular tissue of the remaining part of the tuber. Only when the fungus was present or absent at all of these three places simultaneously was the tuber regarded as infected or free from infection respectively for the purpose in view.
It may be stated that the mycelium can be traced definitely growing out of the browned xylem portions of the vascular ring of the tuber, and, indeed, the exit of an individual hypha from the cavity of a particular wood vessel has in many cases been traced, so that there can be no doubt as to the source from which the fungus comes. Occasionally the growth of other fungi makes certain determination practically impossible, and this is especially the case when Hypochnus Solani is present on the surface of the tuber under examina- tion, for it rapidly produces a luxuriant growth at the expense of the cells killed by the process of cutting. ven in such cases, however, with some experience it is sometimes possible to discriminate between the growth of
Peruysripge— The Verticillium Disease of the Potato. 73
Verticillium emanating from the wood vessels and the coarse mycelium of Hypochnus covering the cut surface.
In the autumn of 1914 twenty-five tubers which were proved conclusively to contain the fungus, by testing as above described, were selected. In the third week of October, i.e. soon after they were dug, these tubers were each eut into two portions, a heel portion and a rose portion, each possessing eyes, the heel portions being as a rule larger than the corresponding rose portions. The fifty sets thus obtained were then indelibly marked with Indian ink, so that they could not possibly become mixed. They were placed in a sprouting box and allowed to remain there over winter. In the spring all of them had produced normal sprouts from the various eyes.
In January, 1915, a further set of twenty-five tubers was selected which were found on testing as before to contain the fungus. These were also allowed to sprout in a box, which they did in normal fashion. In April, a day or two before planting, these tubers were each cut into two portions, roses and heels respectively. The tubers cut in the autumn and in the spring were all selected from the same lot, and were the produce of affected plants grown in 1914.
At planting time in 1915, therefore, there were sets from twenty-five autumn-cut tubers, and a similar number from spring-cut ones. Five pairs of each were grown in pots in Dublin in a cool greenhouse, while the remainder were planted at Clifden. No farmyard manure was used in either case. The resulting plants, some of which were diseased and some healthy, were carefully examined for the presence or absence of mycelium in their stalks. In the cases of the healthy plants, where no mycelium was found, they were allowed to grow until the close of the season, when they were dying naturally, so that the absence of mycelium was not due to the plants having been examined too early.
A summary of the results is given in the following table :—
= mre <i Diseased Health °/, diseased No. and description of | No. of plants | No. of 5 Be OF pa plants with plants without ot those
Sua Demi, developed. | misses-| Verticillium. | Verticillium. developed. 25 Autumn-cut. Heels. 23 2 21 2 91 26 do. Roses. 24 1 16 9 63 25 Spring-cut. Heels. 23 2 22 1 96 25 do. Roses. 25 0 19 6 76
mM 2
74 Screntific Proceedings, Royal Dublin Society.
With regard to the “ misses,” these were due in the two cases of autumn- cut heels to the sets succumbing apparently to a soft bacterial rot. In the spring-cut heels the miss in one case was evidently due to the attacks of slugs, and in the other a weak shoot had developed from the small set, which, however, had also been attacked and was not strong enough to reach above ground. Verticillium was found to be present in the vascular tissues of the remaining more or less sound portions of these sets in July. The miss in the case of the autumn-cut roses was due to the removal of the set, probably by a rat or a jackdaw, as both of these animals were observed at various times to be active in this manner on neighbouring plots. It is not believed that the presence of Verticilliwm albo-atrum in the sets was the cause of any of these misses. This point will be referred to again later in this paper.
It is scarcely necessary to go into the details of the development of the plants from these various sets; suffice it to say that many of them, from roses as well as heels, were small from the start and soon showed signs of the disease, dying away soon after the middle of July. Others were larger and lasted longer, while comparatively few lasted out the season. In all cases in the table where the plants are described as containing Verticillium, it should be understood that this was determined both by microscopic examination and by cultural methods. The same methods were applied and gave negative results in the cases of the plants described as being without Verticillium.
It will be seen, as was to be expected, that a very high percentage of the heel-end sets, both autumn-, and spring-cut, gave diseased plants ; nevertheless a few of them gave healthy plants, from which it follows that an affected set or tuber, although it generally gives rise to a diseased plant, does not neces- sarily do so. Further evidence of this will be adduced presently. It may also fairly be concluded that even in the autumn the fungus must have reached in very many cases (sixty-three per cent. in this particular experi- ment) the rose-end half of the tuber, and that consequently it is not correct to regard the fungus as generally hibernating in a more or less strictly localized position at the very heel-end. -
Further, since the percentage of diseased plants arising from the spring- cut rose sets is considerably higher than that of the corresponding autumn-cut ones, it may be concluded that the mycelium does make some progress from the heel towards the rose-end of an affected tuber during storage over winter.
The fungus has been isolated from the vascular tissues of various regions in tubers both before planting and also at the close of the season when they have produced diseased plants. (See fig. 1, Plate III.) It has never been observed to spread from the wood vessels to the surrounding tissues in the
Peraypripce—The Verticillium Disease of the Potato. 75
tubers as it does in the stalks, and the black sclerotial form of the mycelium has not been found in the tubers. It is true that affected tubers, when kept unplanted till the late summer, often show, when cut across, a strong blackening in the region of the vascular ring; but microscopic examination shows that this blackening is not due to the presence of mycelium, but to some colouring matter produced in the cells in this region.
From what has been said, it seems clear that the mycelium of the fungus which is present in the tubers produced by affected plants—and very few of the tubers produced by such plants are free from it—is located in the wood vessels of the vascular tissues and is confined to them. But it is by no means necessarily localized at the heel-end of the tuber, and may probably spread slowly in the vessels of the tuber during winter storage. Judging from the varying amount of aerial growth produced at the cut surfaces of the vessels of affected tubers when suitably incubated, it seems likely that the amount of mycelium present in such tubers may vary considerably, and that thus one tuber may be more strongly infected than another.
It is quite conceivable—although it has not definitely been proved— that the strongly infected tubers give rise to plants which show the disease early and soon die off, and that the less strongly infected ones produce plants which attain more normal size, and which do not show symptoms of the disease until considerably later. Finally, the fact that affected tubers occasionally produce healthy plants may be explained by the original infection of the tuber being so slight that the fungus was unable to reach the plant developing from such a tuber before the conclusicn of its growth.
VY. PRopDUCTION OF DISEASED PLANTS FROM AFFECTED TUBERS.
According to Reinke and Berthold, when affected tubers are planted, the fungus grows over the outside of the tuber in the cork cells, and so reaches the young sprouts through the cortical portions of the young roots. This idea was based chiefly on the fact that Verticillium was found growing on the skin of the tubers as well as in the cortical portions of roots and young stems. It does not follow, however, that the Verticillium found in such situations was in reality V. albo-atrum, and I am of opinion that Remke and Berthold were misled by an assumption of this kind. I have found two apparently new species of Verticilliam (which will be described in detail in another paper) which occur on potato tubers, and which in the conidial form might easily be mistaken for V. albo-atrum, but which, when grown in pure culture, are clearly quite different from it and from each other. Neither of these species is capable of producing a disease of any kind in the potato; they are both pure saprophytes.
76 Scientific Proceedings, Royal Dublin Society.
It is much more reasonable to suppose that the fungus present in the wood vessels of the tuber passes from them at some time or other directly into those of the developing sprouts; and although this passage has not been definitely traced while it is taking place, yet there is every reason to suppose that it does occur.
There would be considerable difficulty in following the course of the mycelium from tuber to developing stalk while this is actually taking place, particularly because the passage does not appear to occur until after the sprouted tuber has been planted, and the young shoots have made considerable growth.
During the several seasons over which this disease has been studied, no evidence has been obtained that the presence of the fungus in the tuber interferes with the production of sprouts; on the other hand, affected tubers have always been found to sprout normally, and to be indistinguishable from healthy ones in this respect.
According to Miss Dale! Verticilliwm albo-atrwm is a cause of “ blindness ” (non-development of sprouts) in potatoes. It seems clear, however, from her description that this author was not really dealing with this species of Verticillium at all, for it never forms “small rounded segments containing numerous drops of oil,” although one of the two new species referred to above does this. The species associated with “blindness” was found in the epidermal and cortical tissues, and not, apparently, in the wood vessels. Further, no infection experiments were made, and it is quite possible that the “ blindness” was due to some other cause, while the Verticillium present was simply living saprophytically on the dead tissues.
The following observations show that the fungus in the wood vessels of the tuber does not pass at once into the developing sprouts. Seven tubers from affected plants were tested in September, 1914, and were found to contain mycelium of V.albo-atrum. They were allowed to sprout in a box during the winter—which they did normally—and remained unplanted till the third week in July, 1915. At this time the tubers were somewhat shrivelled owing to loss of water, and each had produced several sprouts of varying lengths from the eyes situated both near the rose and heel ends of the tubers. A further test was then made of the tubers, and it was found that the mycelium in their vessels was still living. All the sprouts of each tuber
1 Dale, E., On the Cause of ‘‘ Blindness” in Potato Tubers. Ann. Bot., vol. xxvi, 1912, p. 129. I cannot, however, follow Wollenweber, who says (Phytopathology, iii, 1913, p. 40) that Miss Dale’s Verticillium is probably “ Periola tomentosa (Fr.), Reinke and Berthold (1879) [sic] . . . only resembling Verticillium macroscopically.”” As far as I have seen it, Periola does not resemble a Verticillium even macroscopically.
PretnyBripGe—The Verticillium Disease of the Potato. Uh
were then subjected to careful microscopical and cultural examination, but in no single instance could the fungus be found present in a sprout. In one case it was found in the wood vessels of a tuber close to the point of origin of the sprouts, but even here the sprouts themselves were free from it.
The young shoots produced by affected tubers always appear healthy (although they may be small) when first they come above ground ; and if they are examined microscopically at this stage, mycelium may not be found in their wood vessels. But if they are allowed to remain longer, sooner or later symptoms of disease will begin to develop in their foliage, such as rolling of the leaflets, or dying off of the lower leaves. When this occurs, or at any rate very soon afterwards, mycelium will be found in the wood vessels of the lower portions of the stalks at least, while often it has not yet reached the upper parts. This mycelium has been traced down the stalk, back to the point of insertion of the latter on the parent tuber, and finally into the wood vessels of the tuber itself at this point, thus permitting of no reasonable doubt but that it has grown from the wood vessels of the tuber into those of the stalk. No evidence was found of the presence of the fungus in the cortical tissues of these stalks, and consequently it could not have reached the wood vessels from this source. Hence it is believed that the mycelium reaches the young stalks, not by growth over the outside of the tuber, as Reinke and Berthold supposed, but by direct growth through the xylem system common to tuber and stalk.
There is, however, a distinct pause of longer or shorter duration before the mycelium proceeds from the tuber to the stalk, during which temporarily healthy stabks are developed from affected tubers. If this pause is sufficiently prolonged, either because the amount of mycelium in the tuber was originally very small, or its location was removed so far from the developing shoot that the latter could not be reached in time, then it is possible to understand how an affected tuber may give rise to a plant which remains healthy throughout the season, and which produces healthy progeny.
Statistics compiled for the seasons 1912-1915 show that when affected tubers are planted 96 per cent. of them give rise to diseased plants bearing further affected progeny, while the remaining 4 per cent. produce healthy plants with healthy progeny.
VI. Tue FuNGUS IN PURE CULTURES.
Since when placed under suitable conditions of moisture and temperature, the fungus present in infected tissue grows out into the surrounding air, and produces ‘a plentiful crop of conidiophores and conidia, it is a com-
78 Scientific Proceedings, Royal Dublin Society.
paratively easy matter to obtain it in pure culture. This has been done in several instances by planting out the conidia in gelatine media either directly or after a first transference to suitable slants in test-tubes, or to media previously allowed to set in Petri dishes. In this last-named way it is possible to exercise microscopic control over the growth which develops from the inoculating material; and platings of conidia from growths of this kind, which are found to be free from bacterial or other contamination, have always given pure cultures. In some instances the additional precaution was taken of making successive platings before arriving at the particular culture destined to serve as a stock from which cultural and other studies were to be made.
The fungus has also been isolated from the vascular tissue of affected tubers both before planting and after they have been planted and have given rise to diseased plants. It frequently happens that the parent tubers from which diseased plants are developed are to be found at the close of the season more or less completely hard, sound, and not fully depleted of their reserve food materials. In such tubers the woody tissues containing the fungus are strongly browned, as shown in fig. 3, Plate III. Cultures from tubers were obtained by transferring—under conditions of asepsis—portions of the affected woody tissue direct to suitable media in slants or on set plates. Some of these direct transfers proved to be pure from the start, while others of course were contaminated by the presence of other organisms, especially in the case of old tubers; but even in these latter instances Verticilliwm albo- atrum was always present, and by further work could be obtained in pure culture. :
The fungus grows well as a saprophyte on a variety of media such as Quaker Oat agar, oat-extract agar, wort gelatine, cooked potato agar, potato- stalk agar, cooked potatoes, cooked potato-stalks, and beef extract agar and gelatine.
It produces both aerial mycelium bearing conidiophores with conidia and submerged mycelium. There has been a tendency during the period of over two years through which the cultures have continuously been propagated for the relative proportion of aerial mycelium developed to diminish. Both the aerial and the submerged mycelium is at first pure white in diffused light, but in the course of time black submerged mycelium is produced just in the same way as occurs in the stalks of affected plants, and the medium therefore becomes blackened. This blackening is due solely and entirely to the blackening of the mycelium, and not to the production of dark chlamydo- spores, as occurs in the two other species of Verticillium already alluded to.
Pretuysripcr— The Verticillium Disease of the Potato. 79
On certain media, viz., beef extract agar and gelatine and potato-stalk extract gelatine, this blackening of the submerged mycelium does not occur at all. Further, although the fungus readily develops this black submerged mycelium (except on the media just mentioned) when cultivated soon after its isolation from the potato, yet in the course of time, after prolonged cultivation on these media, its power of producing black submerged mycelinm gradually diminishes until it becomes entirely lost.
Most of the cultures were kept in the diffused light of the laboratory, but a special comparative series was made to see whether light exercised any influence on the behaviour of the fungus. Parallel cultures were for this purpose (a) kept in total darkness, and (0) exposed directly to daylight in a window facing north but protected from direct sunlight. No very striking differences were observed in the cultures, but in the dark the aerial growth was pure white, while in the light it took on a faint pink fringe, and the blackening of the submerged mycelium which occurred both in the dark and in the light began to be perceptible in the cultures kept in the dark slightly sooner than in those exposed to light. On all the gelatine media used liquefac- tion of the gelatine invariably occurred. This took place perhaps somewhat slowly: but in slants in test-tubes the medium was usually completely liquefied in cultures at room-temperature one week old.
Many attempts were made to cultivate the fungus on living potato tubers and on cut portions of living green potato-stalks, but without success. A limited amount of development occurred in the cells injured by cutting or making the inoculation. In the case of the cut stalks further growth took place only when they had been standing for such a long time that they had begun to die. In the case of the tubers or cut portions of them no further growth took place, and a layer of cork was developed beneath the wounded surface. Hence, although the fungus is a vascular parasite of the potato, it is quite incapable of causing a rot of the living tubers or stalks.’
The morphological characters of the fungus were accurately described and figured by Reinke and Berthold, and its growth in pure culture has not resulted in the necessity of altering or adding to the description given by them. It is believed, however, that the species which these authors met with living on the skin of the tuber and in the cortex of the stalks below ground was not the same as that inhabiting the wood-vessels, but probably one of the two already referred to, which develop dark-coloured chlamydospores on their submerged mycelium.
1 The opposite results obtained by Carpenter (Journ. Agric. Research V, No. 5, 1915, p- 203) are, as he himself points out, doubtful, and were probably due to imperfect experimental methods.
SCIENT. PROC. R.D.S., VOL. XV., NO. VII, N
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In spite of prolonged culture on varied media, Verticilliwm albo-atrum has not been found to produce any other reproductive bodies such as perithecia, nor has it ever produced chlamydospores of any kind.
VII. Inrection EXPERIMENTS.
The first attempt at producing the disease by suitable inoculation of a healthy plant was made at Clifden inthe summer of 1909. The inoculation was made by inserting a portion of the woody tissue containing the fungus, obtained from a diseased plant, into a freshly prepared wound made to the depth of the wood just above ground-level in the stalk of a healthy plant, taking precautions to avoid, as far as possible, contamination with other micro-organisms. After nineteen days there were no distinct outward signs that infection had occurred ; but as the foliage of the plant was beginning to be destroyed with the ordinary blight, it was decided to break off the experi- ment at this point. Sections of the inoculated stem showed the presence of fungus mycelium in the wood vessels to a distance up the stem of twenty centimetres from the wound; and on suitable incubation it proved to be that of Verticillium. Hence it appeared probable that there would be no difficulty in transferring the disease by inoculation.
In the foregoing case of course a pure culture was not employed, but in 1914 several series of infection experiments were made with pure cultures. Those of the first series were carried out on plants in pots in the greenhouse of the Seeds and Plant Disease Division of the Department of Agriculture in Dublin, and were as follows :—
The plants for the experiments were grown from previously sprouted healthy tubers from which all the eyes except the strong terminal one were excised. This was done in order that each plant might have but one sub- stantial sprout or stalk suitable for inoculation. Inoculation was made in all cases by introducing portion of a pure culture into wounds carefully made in the sprouts or stems at a node, precautions being taken to prevent contamina- tion by other micro-organisms. After inoculation the wounds were carefully covered with tinfoil, and were thus not allowed to come into direct contact with the soil. In every case where an inoculation was made a similar sprouted tuber or plant was treated in the same way, except that no portion of a culture was introduced into the wound; and this served as a control. In this particular series there were eight plants inoculated at four different periods, together with their eight controls. Some of them were inoculated in the sprouts before planting, others when the shoots were only about two inches above the soil, and the remainder at correspondingly later dates. Symptoms
Preruysripge— The Verticillium Disease of the Potato. 81
of disease began to appear in the earlier inoculated plants about one month after inoculation ; but in those inoculated later, when the plants were much larger, the symptoms first appeared within about seven days. The symptoms were the appearance on the older leaves of pale green or yellow areas with rather ill-defined margins. After a time these areas dried up and became brown and dead. Gradually these symptoms repeated themselves in the successively younger leaves, often but not always accompanied by an inrolling of the margins of their leaflets. In some cases the leaves while still green showed a true wilting due to loss of turgor in their cells; and by degrees the foliage of the inoculated plants died off by a process of desiccation proceeding from below upwards. When the foliage was dead, a similar process of desicca- tion took place in the stalks proceeding from above downwards. When the inoculations were made while the plants were still young, the inoculated plants remained much smaller than the corresponding controls; but this difference, although present, was not so marked in the case of plants inoculated when already fairly advanced in growth. A good idea of the kind of result obtained in this series of inoculation experiments is afforded by figs. 3 and 4, Plate II.
When the discolouring leaves showing the first symptoms of disease in the plant were removed and placed in a moist atmosphere, they quickly became covered externally with an aerial development of conidiophores of Verticillium, thus proving that the fungus had already reached them. Sections of the veins and petioles of such leaves showed the abundant presence of the mycelium in the wood vessels. The same mycelium was also found to be present in the stems, roots, and some of the new tubers of the inoculated plants at the conclusion of the experiment. It was an easy matter to obtain the fungus in culture from dead or dying plants, and to prove by the character of the black submerged mycelium developed in due time that it was Verticilliwm albo- atrum.
The control plants were just as carefully watched and examined for the presence of the fungus as the inoculated ones, but they showed no signs whatever of disease, and no mycelium could be found in their vessels; in short, they remained perfectly sound, and produced sound tubers.
The second series of inoculation experiments was carried out in one of the gardens at the Albert Agricultural College, Glasnevin, in the open ground. Six previously sprouted healthy tubers were inoculated in the sprouts before planting, and six plants from healthy tubers were inoculated in their stalks below ground in the manner previously described, when they were about 30 cm. high. There were twelve controls. All of the inoculated plants remained smaller than the corresponding controls. They soon began to show
n 2
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the characteristic symptoms of the disease, and they died off prematurely, whereas the controls behaved normally. Microscopic examination of the inoculated plants showed the fungus present in all their organs, including some of the new tubers. Similar examination of the controls showed that ten of them were quite free from the fungus. In the case of one of the remaining two, it was found in the vessels of a single rhizome, but in no other portion of the plant, and in the case of the other it was present in the vessels of some of the roots. These two plants were growing in close proximity to two of the inoculated plants, and it is quite possible that the rhizome and the roots may have become infected by coming into contact with the diseased roots or rhizomes of these neighbouring plants; it would have been better if the controls had been planted at a greater distance from the inoculated plants.
A further series of inoculation experiments was carried out in the field at Clifden, there being four inoculated plants and four controls. Two of these and the corresponding controls were on plants of the variety Up-to-Date, which was the one used in the previously described series. The controls remained perfectly sound, while the inoculated plants became diseased, and were found to contain the fungus in all their parts, as in the cases already described.
The other two inoculated plants and the corresponding controls at Clifden were, however, of the varieties Shamrock and Northern Invincible respectively. Both of these varieties have proved themselves to be resistant to the attacks of blight (Phytophthora infestans), the former very highly so and the latter slightly less highly. The method of inoculation was the same as that employed in the previous experiments. The plant of Northern Invincible became diseased, and invaded in all its parts by the fungus, just as had been the case with the Up-to-Dates, while some of the tubers also contained it. On the other hand, the symptoms of disease in the inoculated plant of Shamrock were less pronounced, and the invasion by mycelium was much less extensive. The fungus was found in the vessels of the upper portions of the inoculated stem; but just below the inoculating wound it stopped, and it did not proceed further downwards. ‘I'he roots, rhizomes, and tubers were found to be free from it. Hence it would appear probable that this variety is somewhat resistant to this disease, as well as to the blight. The controls in this case also remained sound, and were found to be free from mycelium.
Still further inoculation experiments were carried out on cut stalks placed in Tollens’ nutrient solution, and kept under observation in the labora- tory. It is not necessary to deal with these in detail; suflice it to say that the fungus spread from the inoculating wound in the vessels, both up and
PrruyBRiDGE—The Verticillium Disease of the Potato. 83
down the stalk, butin a somewhat less vigorous fashion than where the stalks remained on the plant.
Some of the tubers produced by inoculated plants in 1914, which investi- gation showed contained the mycelium of the fungus in their vascular tissues, were planted in 1915, and gave rise to diseased plants, which could not be distinguished from similar plants arising from infected tubers produced in the previous season by naturally diseased plants.
Berthold and Reinke carried out infection experiments with the fungus, but, of course, not in pure culture. A considerable number of them gave negative results, particularly when the inoculations were made only into the parenchymatous tissue of tubers, or that of the cortex of stems. Positive results were, however, obtained, when the inoculation wound included a portion of the woody tissue, and the inoculated plants showed their type A of the disease.
The experiments described conclusively show that Vertcedlliwm albo-atrum is an active parasite capable of luxuriant growth and development in the larger vessels of the woody tissue of the potato, and that it is the direct cause of the disease described.
Tn the cases of the disease studied by the present author the source of the infection of the plant has generally been due to the planting of affected seed-potatoes, and no experiments have yet been carried out. to ascertain the way in which primary infection of plants derived from healthy tubers might occur under natural conditions. Reinke and Berthold showed that when a young root was brought into contact with the mycelium of the fungus, the latter penetrated into the superficial tissues of the root, but apparently it did not reach the vascular tissues. Infection experiments with conidia placed on the surfaces of young roots did not succeed, as the conidia did not germinate. It seems probable that primary infection may occur directly from the fungus living as a saprophyte in the soil; but further experiments in this direction with pure cultures of the fungus are necessary before a definite conclusion can be drawn. Miss Dale claims to have isolated Verticwliwm albo-atrum from a sandy soil, and cultivated it on various media. Since it is stated that the fungus in all its stages is a pure white, it might seem improbable that it was in reality V.albo-atrum. Nevertheless, in view of the fact that the fungus when grown for a long period as a saprophyte gradually loses its power of producing black mycelium, it is possible that the same loss had occurred owing to a prolonged period of saprophytic growth in the soil. In a case of
1 Dale, E., On the Fungi of the Soil. I. Sandy Soil. Annales Mycologici, x. No. 5, 1912, p- 465.
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this kind, suitable inoculation experiments with potato plants would enable a definite decision to be made.
VIII. RELATION OF THE VERTICILLIUM DISEASE TO “CURL” AND © LEAF Row.”
The term “Curl” has long been in use for certain potato troubles. A disease known by this name is said to have been seen first in England so long ago as 1764; and towards the end of the eighteenth and during the early part of the nineteenth centuries it was the subject of much discussion by agricultural writers of the day. The literature on the subject is very extensive, but, unfortunately, in the main it is most unprofitable reading. From a study of this literature it is impossible to obtain an accurate idea of what the Curl really was, for most of the writers on the subject preferred exercising their imaginations in speculations as to the probable causes of the disease and in formulating remedies for it, rather than attempting to give a careful description of the symptoms which characterized it. It is quite possible, and indeed probable, that the term “Curl” was applied to more than one distinct disease of the potato; and this supposition, if correct, would serve to explain the conflicting opinions often published concerning it. Anyone who wishes to get an insight into the complexity of the views concerning “Curl” which prevailed during the early part of last century cannot do better than consult such a summary of them as that published in 1804 by Forsyth.!
Apparently as time went on the trouble known as “ Curl” became less serious, and in the middle of the nineteenth century it was for a time quite overshadowed in importance by the epidemics of blight from which the potato crop then suffered. Nevertheless, it is clear from Hallier’s’? account that the disease (Krauselkrankheit) was still prevalent in the early seventies of last century in many districts in Germany. Hallier’s description of it would lead one to believe that it was one caused by a specific fungus inhabiting the vessels of the wood, and perhaps identical with the Verticillium disease described in the present paper. He himself certainly adopted this view, and named the supposed fungus Rhizoctonia tabifica. It is clear, however, that Hallier applied this name not to a single fungus, but to more
1« The Principles and Practice of Agriculture,’’ systematically explained, in two volumes; being a treatise compiled for the fourth edition of the Encyclopedia Britannica, and revised and enlarged by Robert Forsyth, Hsq. Edinburgh: Constable & Co., 1804. See particularly p. 174 et seq.
2 Hallier, E., ‘‘Die Ursache der Krauselkrankheit.” Zeitsch. f. Parasitenkunde, iv, 1875, p. 97.
Preruysripge—The Verticillium Disease of the Potato. 85
than one of those which are frequently found growing together on dead or dying potato-stalks.! The principal literature on Curl (Krauselkrankheit), from Kiihn’s time onward, is dealt with by Reinke and Berthold in their paper already referred to, so that it is not necessary to go further into the matter here. It seems fairly clear that what is in the present paper called the Verticillium disease was sometimes included in what was called Curl (Krauselkrankheit) in the seventies of the nineteenth century. Whether, however, the disease called Curl in the previous century applied solely to the Verticillium disease is another question. On the whole, it seems likely that it was only one of the diseases covered by this term.
There is another form of “Curl” to which I called attention in 1912,° which cannot well be confounded with the Verticillium disease, and the cause of which is quite unknown. Affected plants are small, and their foliage is very much crumpled and curled. No fungus is present in the plants; they produce few and only small tubers, which reproduce the disease when planted. In the cases studied by me the tubers produced in successive seasons became smaller and smaller until, finally, they were not large enough to remain alive until the spring, so that the race of abnormal plants died out completely. This form of Curl has also been recognized in Germany and in America, the term “curly dwarf” having recently been applied to it in the latter country.
Again, in England the term “leaf-curl” has recently been applied* to a potato disease said to be due to Macrosporiwm solani (Cooke), but which still lacks proper scientific study and investigation. Further, Vanha,* in 1910, regarded a new fungus (Solanella rosea) as being responsible for a potato disease, which he designated “curl” or “roll” disease (Krausel- oder Roll- krankheit), without, however, bringing forward really convincing evidence.
Without going any further into the matter, it is quite clear that the term “Curl” (or “Leaf-Curl”) has been applied to several probably distinct diseases of the potato, and it would therefore be well to refrain from the use of it in future.
In 1907 Appel® published a leaflet describing a disease of the Apeteta which
1 The sclerotium, with appendages, described and aan iy Hallier as a resting oe of his R. tabifica, is, I have discovered, an early stage in the formation of its fructitication by a species of Colletotrichum, which I hope to describe elsewhere.
2“ Jour. Dep. Agric. and Tech. Instr. Ireland,’’ xii, 1912, p. 304.
3“ Journal Board of Agric.,” vol. xii, 1905-1906, p.476. Ib., vol. xiii, 1907-1908, p. 466.
4 Vanha, J., ‘‘Die Krausel- oder Rollkrankheit der Kartoffel, ihre Ursache und Bekampfung.’”’ Monatshefte f. Landwirtschaft, iii, 1910, p. 268.
5 Appel, O., ‘‘Die Blattrollkrankheit der Kartoffel.” Kais. Biol. Anst. f. Land- u Forstwirtschaft. Flugblatt 42, 1907.
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was then prevalent in Germany and some of the neighbouring countries. The disease was stated to be by no means a new one, but rather one which had hitherto been included amongst that congeries of diseases known as “Curl” (Krauselkrankheit). To this particular form of disease the name Blattrollkrankheit (“Leaf-Roll” disease) was given, and one or more fungi (not specifically named) belonging to the genus Fusarium were said to be the cause of it.
This publication may be looked upon as the first of a long series of others which followed dealing with “Leaf-Roll.” In some of these Appel’s results are confirmed, and to some extent amplified. Thus, not only was a Fusarium found to be the cause of the disease, but in many cases the parasite was found to be Verticilliwm albo-atrum.! On the other hand, many students of the “ Leaf- Roll”’ disease stoutly maintained that it was not due to a fungus at all, for the simple reason that the presence of a fungus in the vessels (as described by Appel) was by no means a constant or, in some cases, even frequent symptom of the disease. Thus arose a controversy between those who regarded this disease as of parasitic origin and those who maintained the contrary, and who explained it as being due perhaps to the upsetting of enzymic equilibrium, or some other such occult cause. It is not necessary to deal here with the literature which this controversy brought into existence ; suffice it to say that had the upholders of the non-fungus theory of the cause of “ Leaf-Roll” been acute enough to realize that the disease with which they were dealing was not the “ Blattrollkrankheit ” as first defined by Appel at all, but something quite different, the controversy would probably never have arisen. However, the development of this controversy need not be regarded as having served no useful purpose, for it has certainly been the means of stimulating research into some of the more obscure diseases of the potato, from which good results have followed.
It will be seen then that just as the term “Curl” is not applicable strictly to any one specific disease, so the term “Leaf-Roll,” although introduced to apply to the specific disease caused by species of Fusarium invading the wood