Transactions Bose Institute. Vols. Ill and IV ; 1920. 192 i

LIFE MOVEMENTS
IN PLANTS

BY

SIR JAGADIS CHUNDER BOSE

LONGMANS. GREEN AND CO.
CALCUTTA, BOMBAY, MADRAS
LONDON AND NEW YORK

LIFE MOVEMENTS IN PLANTS

BY THE SAME AUTHOR

RESPONSE IN THE LIVrNfi AND XOX-LIVING. With

117 illustrations, 8vo. Ws. 6d. .. ... VM2

PLANT RESPONSE: AS A MEANS OF PHYSTOLOfJl-
GAL INVESTIGATION. With 278 illustrations, «vo.
2l8. ... ... ... ... ... 1906

COMPARATIVE ELECTRO-PHYSIOLOGY: A PHYSICO-
PHYSIOLOGICAL STUDY. With 40H illustrations,
8vo 15«. ... ... ... ... 1907

RESEARCHES ON IRRITABILITY OF PLANTS. With

190 illustrations, 8vo. lO.s. Hrf. net. ... ... 191.'^

LIFE MOVEMENTS IN PLANTS. Vol. I. With 92 illus-
trations, 8vo. lO.v. 6d. ... ... .. 1918

LIFE MOVEMENTS IN PLANTS. Vol. II. With 128 illus-
trations, 8vo. 15.S. ... ... ... ... 1919

THE ASCENT OF SAP. With 93 illustrations, Ifis. ... 1922

BY PROF. P. GEDDES

THE LIFE AND WORK OF SIR JAGADIS CHUNDER

BOSE. With portraits and illustrations, 8vo. 16s. 1920

V

tj^^^^is Bosc Instilutc. Vols. Ill and IV; 1920, 1921

LIFE MOVEMENTS
IN PLANTS

Vol.--.

BY

SIR JAGADIS CHUNDER BOSE

KT., M.A., D.SC, LL.D., F.R.S., C.S.I., CLE.

PROFESSOR EMERITUS, PRESIDENCY COLLEGE
DIRECTOR, BOSE RESEARCH INSTITUTE, CALCUTTA

WITH 107 ILLUSTRATIONS

LONGMANS, GREEN & CO.

HORNBY ROAD, BOMBAY

6 OLD COURT HOUSE STREET, CALCUTTA

167 MOUNT ROAD, MADRAS

LONDON AND NE^V YORK

1923

PRINTED AT CALCUTTA BY CANOES PRINTING COMPANY, LIMITED

PREFACE

The })iiblicatioii of the third and fourth volumes of Transactions
for 1920 and 1921 had l)eeii greatly delayed oii account of my
prolonged absence in Euro[)e, and of post-war difficulties in
publication. The fifth volume of the series for 1922, " On
the Ascent of Sap " is expected to be published at about the
same time as these.

The present two volumes will be found to contain accounts
•of investigations on geotropism, on dia-heliotropic attitude of
leaves as regulated by transmitted nervous impulse, on assi-
milatory and dissimilatorv changes under light, on new methods
of recording the effects of protoplasmic changes under stimulus;
and also of various methods and a])p]iances for detection of the
two fundamental reactions to which all ]>lant movements are
due. In regard to geotro])ism of higher plants, electric investi-
gations have been described which lend strong support to the
theory of statoliths, indeed practically confirm it. Investiga-
tion by means of the Electric Probe has made it possible to
explore the interior of the ])lant, and nu^p init the excitatory
<?hanges from layer to layer under the stimulus of gravity.
The results of these investigations show that while the layers
■of tissue contiguous to the upper perceptive layer undergo a
contraction, those contiguous to the lower perceptive layer
•exliibit an expansion. The cause of tliis difference has also
been discovered in the fact that the geotropic stimulus due to
the pressure of heavy particles acts directly on the upper, and

vi PREFACE

indirectly on tlic lower layer of the rcsponditi^^ cells. AnotluT
discovery, namely, the critical angle for immediate geotropic
excitation, also lends fresh and indejiendent snp])ort to the
theor\ of statoliths. .Vn c.\|ilanation of tlu' dia-geotropisni of
dorsi-ventral organs has heen found in the differential exeit-
ahility of the two sidi's of the organ. In regard to the
dia-hcliotropic attitude of many leaves, it is shown to be due
to transmitted impulse of a nervous character initiated in th(
lamina and conducted to the motile organ. Tlu> jiervrais tissue
which conducts excitation has been localised in the |)li'oem of
the lihro-vascular hundle. As regards the pulvinus of Miuiona
it is found to be a highly com|)lex organ, each of its four
quadrants responding in a definite way by a down- or ui)-move-
nuMit, or by a right- or left-handi'd torsion.

The method of resistivity- variation has been further per-
fected and the responses of the vegetable tissue to various modes
of stimulation — mechanical, electric, and photic — have been
recorded. Tlu' characteristic responses have been shown to
correspond to the mechanical and electromotive responses.
The new (Quadrant method has l>een rendered extremely
sensitive, i>nabling us to record the response to light emitted
by a single spark.

The response of the plant is modified by the changing
intensity of light during the course of the day; but no sensitive
a])pliances had hitherto been available for the continuous record
oi the variation of light. This diriieulty has been overccme by
the invention of the Automatic Kadiograpli.

The movement of plants is affected by the ascent of sa]>
which causes an increase of turgor in the tissue. Prolonged
investigations on the " Physiology of the Ascent of Sap
lia\(' sliown that the propulsion of sap is brought about by
the pulsating and ))umping action of the cells of tliL
inner layer of the cortex; it is also shown that the state
of turgor of the plant at any hour of the day is determined by

PREFACE Vll

the gain or loss of liquid by the plant, the relative variations of
which are definitely traceable to external agencies.

In the general review it has been shown that the innumer-
able variations in response are produced by the different com-
binations of numerous factors, some concordant and othei's
antagonistic. This is the secret of the great complexity of the
plant movements, which are by no means capricious. By the
isolation of individual factors and separate investigations on
them, it is })Ossible to unravel the complexity and discover a
generalisation for the life-movements in plants.

BosE Institute, Calcutta, J. C. Bosb.

October, 1921.

CONTENTS

VOLUME TIT.
CHAPTER LIT

ox ELECTRIC LOCALISATION Ol THE GEO-PERCEPTI VE LAYER.

PACE

The metliod of Electric Probe— Theory of statoliths —
Geo-electric distribution at upper and lower sides — Effect
of seasonal variation and of temperature — Maximum excit-
ability of the geo-perceiDtive layer — Decline of geo-electiic
excitation at increasing distance from the perceptive
layer — Geo-electric response at the under side — Duplica-
tion of the geo-perceptive layer — Effect of age. ... 599

CHAI'TER LITl.

the relation between the angle ok i nci. i nation and the
geo-elp:ctric excitation.

The excitatory reaction at 45° and 9()°— Excitatory
reaction at 45°, 55°, 65°, 75°, and 90° — Tncrease of excita-
tion at larger angles, relatively to sines of angles of
inclination — Excitation at 135° greater than at 45° —
Reactions at upper and lower sides of the horizontally
laid organ. ... ... ... ' ... ... 619

CHAPTER LIV.

THE critical ANGLE FOR GEO-ELECTRIC EXCITATION.

Critical sliding angle for displacement of particles —
Effect of repetition on critical angle — Relation of excita-
tions to the ratio of sines of angles of inclination — Deter-
mination of the critical angle for geo-electric excitation —
Effect of repetition on lowering the critical angle — Con-
firmation of theory of statoliths from discovery of the
critical angle ... .. ... . . ... 631

CONTENTS
CTTAPTER LV.

RESEARCHES ON THE EI FECT OF AXAESTHETICS ON GROWTH.

I'AGE.

The method of lecoid — Apph'catioii of aiiaosthotics —
Effect of dose — Three stages of action — Effect of ether
vapour— Effect of chloroform — Death-spasm undei' conti-
nued action of chloi-ofoi-m. .. ... ... (541

CHAPTER LVI.

THE EFFECTS OF ANAESTHETICS ON GEOTROPIC Rt&PONPE.

Induction of geotropic curvature by differential growth
— Difference of reaction in spring and winter specimens —
Effect of ether on geotropic response of Mimosa leaf and
Desitiodiiirn .eaflet — Effect of ether on geotropic response
of growing oigans — Effect of chlorofo'-m on geotropic
response of pulvinated organs — E^ect of chloroform on
geotropic res])ojise of growing organs ... 650

CHAPTKR LVll.

THE EFFECT OF CARBON DIOXIDE ON (JEOTROPIC ACTION.

Immediate enhancement of gcotro])ic icsponse under
carbon dioxide — Arrest and revcisal of response luuler
continued action of carbon dioxide — Effect of CO. on
geotropic response of penduiu-Ie of Tube rose — Effect of
carbonic acid gas on geotropic response of pulvinated
organs — Exjilanation of the geotropic reversal — Effect of
carbon dioxide on giowth — Effect of CO.cn organs con-
tracted under stimulus — Variation of geo-electric response
under carbonic acid— Isolated response of the ujiper and
lower sides of the organ and its variation under carbon
dioxide ... ... ... . ... 659

CONTENTS XI

CHAPTER LVIII.

ox I'HY •BIOLOGICAL AXISOTROPY IXDUCED BY ORAVITATIOXAL

STIMULUS.

PAGE.

Arbitrary distinction between sensitive and ordinary
plants — Antagonistic contractions neutralise lateral move-
raent in radial organs — Anisotropy induced by unilateral
stimulus — Response of curled tendrils — Anisotropy induced
by geotropic stimulus — Relative inexcitability of concave
side — Response to stimulus by straightening of geotropic-
ally ciu'ved organ — Physiological anisotropy reversed in
inverted position of the organ — Changing intei'nal differen-
tiation detected by transformation of response — Abnormal
positive response of geotropically curved organ under
condition of sub-tonicity — Modifying action of anaesthetics
on response — Effects of ether, carbonic acid and chloro-
form— Identical effect of anaesthetics on external and
internal stinuilation ... ... . ... 676

CHAPTER LTX.

THE DEATH SPASM IX GEOTROPICALLY' CURVED ORG.^XS.

Death-spasm of plant organs at critical temperature
■of 60°C. — Critical point of death in the pulsating leaf of
Desmodium — Excitatory character of the death-spasm —
Electrical spasm at death-temperature — Identical critical
point of death exhibited by geotropically curved organ ... 68"

CHAPTER LX.

THE COMPLEX RESPOXSE OF PULVIXUS OF MIMOSA TO TRAXSMITTED

EX CI TAT I OX.

Four " effectors " in M uikjsh pulvinus — Torsional
response under lateral stimulus — Response to electric
stimulation of sub-petioles 1 and 4 and of 2 and 3 — Method
of localisation of nervous tissue in Mimosa petiole —
Electrical variation in different lajers due to transmitted
•excitation — The path of transmission of nervous impulse —
Definite innervation ... ... 695

XII CONTKNTS

CHAI'TKh' LXT.

IN VKSTl CATION ON T)IA CIU* IKOI' 1 SM OF DORS 1 -VENTRAL ORGANS.

PMiF

No specific sensibility in dia geot ropir oigans — Dia-
ueot roi)ic response of pulvinus ot" M imosii coiuevted into
negative response after inxcrsion of tlie organ — Dia-
gcoti'opie response due to different iai action of stimulus of
gravity on anisoti'o])ic oi-gans — liesjionse to geotrojjic
stimulation of u])per and lowei- (juadrants of puKinus of
iV////o.sY/ — Rpsj^onse of riglit and left flanks of the oigan
to stimulus of gravity — The statolithic appai-atus
in |)ul\inus and in stem — Stimulation of th(> nerve by
pressuic of ))articles — Contraction of u|)i)ei' side of geo-
tropically curved oi-gan e\i)lained by direct stimulation of
nerve — Expansion of lower side due to indirect stimula
tion — Differential geotrojiic stimulation in dorsi-ventral
organs— (ieo-clectric response of radial organs — Geo-
electric resi)onse of dorsi-veutral pulvinus — Explanation
of dia geoti-opic attitude of leaves ... ... 70f^

VOLUME IV.

Ml-.CII WICAI. .\M) l''.LKCTKI) ItESPONSK (JF I'L.XNTS
CHAITI'IR LXIT.

THi: lilA Hi;i,|0ri!01MC ATTITTDE Ol- LEAVES.

The helif)tioi)ic fixed position of leaves — Description
of dia heliotroi)ic phenomenon in motile and in ordinary
leaves- — Characteristics of the motor organ — Mechanical
response due to differential excitability of pulvinus and
of petiole — Itesjionse to stimulation of ada.xial .wm]
abaxial halves of the organ — The diurnal movement of tlir
leaves of M iinosa and Ifclid iitJi iis — Torsional response' to
lateral stimulus — Directive action of projiagated nervous
impulse in heliotropic leaf adjustment — Detection of trans-
mitted imjiulse by electrical and mechanical responses- -
Co ordinated action of transmitted impulses. ...

CONTENTS
CHAPTEPv LXIII.

THE ELECTRIC RESPONSE OF MIMOSA PUDICA.

PAGE.

Transmitted excitation in petiole of Mlt/iosa — Stimula-
tion by equi-alternating shocks — Error (hu- to leakage of
shock current eliminated by choking coil — Electric
resi)onse to transmitted excitation — Effect of excessive
absorption of water -Effect of feeble stimulus — Positive
response of sub-tonic tissues — Conducting path fashioned
bv stimulus. ... ... ... ... ... 751

CHAPTER LXIV.

SIMULTAXEOUS DETERMINATION OF VELOCITY OF EXCITATION BY
MECHANICAL AND ELECTRIC METHODS.

The Mechanical aiul Electric Recorders — The Electro-
metric Method^ — Simultaneous Mechanical and Electric
records — Identical results b> diffei'cnt methods. ... 759'

CHAPTER LXV.

THE MULTIPLE RESPONSE IN MIMOSA.

Response under feeble and I'^ioderate stimulus — Multi-
ple mechanical response iv BiG2)hytum under strong-
stimulus — Multipif electric response in Mimoxn under
strong stimulus — Discovery of multiple mechanical
response in Mimosa under intense stimulation — Conti-
nuity between ordinary and multiple response ... 766

CHAPTER LXV I.

THE EFFECT OF CAJIBON DIOXIDE ON AUTONOMOUS PULSATIONS
OF DESMODIUM GYR.ANS.

Effect of car'oon dioxide on autonomous growth —
Continuity between multiple and autonomous response —
The effect of CO, on mechanical pulsation of Desmodh/m
— Flffect of carbon dioxide on electric pulsatioris ... 771

XIV CONTENTS

CHAPTER LXVII.

IHK TRANSMISSION OF DKATH-F.XC^TATION.

PAGE.

Critical temperature for transmission of death-excita-
tion in J/////O.SV/ — Transmitted death-excitation in Avtrrhoa
causing multiple response — Transmitted death-excitation
caused by local poisoning. ... ... ... 770

CHAPTER LXVIII.

THE SPREAD OF THE WATER-HYACINTH.

Possible methods of destructions of the plant — Danger
of introduction of fungal parasites — Ineffectiveness of the
application of steam — Vegetative proi)agation of the plant
burnt to the water-edge^Discovei-y of the cause of lailure
— Proi)agatioii by submerged root and stolon — In-
effectiveness of the poisonous spray — Poison carried by
ascent upwaids not downwards — Contrasted effects of
application of poison to root and shoot — Application of
poison to the shoot causes local death but not destroy the
whole i)lant ... ... ... .. ... 786

CHAPTER LXIX.

RESPONSE TO MECHANICAL STIMULUS BY VARIATIOX OF ELECTRIC

RESISTANCE.

Method of 1-esponse by resisti\ity \ariation — Device
for mechanical stimulation of graduated intensity —
Additive effect of stimulus — Uniform response by diminu-
tion of electric resistance, under constant stimulus — The
positive after-effect — Effect of chlorofoim in depression of
response — Preliminary enhancement of response under
■i-hloiofoim ... ... ... ... ... 796

CHAPTER LXX.

RESISTIVITY VARIATION OF PLANTS UNDER ELECTRIC STIMULUS.

The method of aj^plication of electric stimulus —
Xoimal negative response by diminution of electric resist-
ance— Resjjonse by increase of resistance under sub-
minimal stimulus — Multiple response by resistivity varia-
tion, under strong stimulus — Effect of carlton dioxide
on response by resistivity vaiiation — Effects of ether and
chloroform ... .. ... 805

CONTENTS XV

CHAPTER LXXI.

THE QUADRANT METHOD FOR RESPONSE OF LEAVES TO STIMULUS

OF LIGHT.

PAGE.

The principle of the Quadrant Method — Its extreme
sensibility — Response to light from a single spark — Effect
of increasing intensity of light. — Effect of carbon dioxide
on response — Effect of vapour of chloroform — Variation of
permeability under stimulus ... ... 814

CHAPTER LXXII.

THE SELF-REC'ORDIXC RADIOGRAPH.

Problem of continuous registration of variation of
light throughout the day — The Selenium Cell— Balaiice of
resistance by Wheatstone Bridge^ — Automatic exposure
and record of intensity of light at different hours of the
day — The Galvanograph — The curves of rise and fall of
intensity of light — The light-noon and the thermal-noon —
Asymmetry of light curves in the fore-noon and in the
after-noon — Diurnal record of light intensity on a clear
day^Record of variations in stormy weather — Diurnal
curves for light and temperature. ... ... ... 825

CHAPTER LXXIII.

ox A VEGETABLE PHOTO-ELECTRIC CELL.

Normal response to light — The electric response
of leaf to light— The vegetable photo-electric cell —
Similar response under mechanical stimulus — Response of
very young and very old leaves— Effect of increasing
duration of exposure — Effect of continued action of light
and its after-effect ... ... ... ... 835

CHAPTER LXXIV.

GENERAL REVIEW ... ... ... ... 842^

ILLUSTRATIONS

FIGURE. PA<"-E.

221. Diagrammatic rei)i('seiitatioii of geo-perceptive

layer ... ... ... ... ••■. 600

222. The Electric Probe ... ... ... ... 601

223

224
225

226
227

228

229
230

231
232
233
.234
235
236
237
238
239
240
241
242
-243

Curve of geo-electr'ic excitation in different layers

(Xymphaea) ■■■ ■■■ ■■■ ••• 603

,, ,, (Bryophyllum) 603

Intensity of geo-elcctric response at different depths

(Tropaeohwi) ... ... ... ... 607

Curve showing geo-electric distribution ... ... 610

Intensity of geo-electric excitation at different

depths of lower side (Tropaeohim) ... ... Oil

Geo-electric response at different deiiths of stem

{Troj)aeoJum) ... ... ... ... H12

Curve showing du|)liration of geo-electric maximuni liliS
Diagrammatic lepresentation of the geo-e'ectric

response of the shoot ... ... ... 620

Alternate geo-electric responses at 45° and 90° 622

Eecords of geo-electric responses at various angles 624

Geo-electric responses at 45°, 135°, and 45° ... 627

Curves of sines and geo-electric excitations ... 634

AV)rupt geo-electric response at 31° ... ... 636

The High Magnification Crescograph ... ... 642

The chamber for application of anaesthetics . . 643

Effect of ethei' vai;)our in enhancing growth ... 645

Effect of chloi-ofoini on gi-owth ... ... 646

Geotropic cui-vcs of spving and winter siMH-imcns ... 652

Effect of ethei- on geotropic resjionse (M imnsa) ... 653

,, ., ,, ,, {DcsuKxli mil ;/l/i /)/!■■<) (553

,, ,, ,, ,, (T ro/Ku-olum) ... 655

ILLUSTRATIONS Wll

flGURK. PAGE.

244. Effect of ether viii^our on geotropism . . ... 655

245. Effect of chloioform on geotropic response {M i iiioxa) G56

246. ,, ,, ,, {/)('s/i)0(/iin/i) ... 656

247. ,, ,, ,, ( h'cli'/)f(i, T roitdcoluiii) 657

248. ,, CO,. ,, {Tropaeolum) ... 660

249. ]\Ietho(l of record of geotropic response of Mimosa

in inverted position ... . . ... 663

250. Effect of CO. on geotropic response of Mimosa ... 664

251. Effect of COj on geotropic response of Eryihriva

indica ... ... ... ... ... 664

252. Effect of CO., on growth ... ... ... 669

253. Effect of CO:.on stimulated organ ... ... 669

254. Electric connections for geo-electric response ... 672

255. Effect of CO;; on geo-e'cctric response of lower side 673

256. Effect of CO:, on geo-electric response of upper side 673

257. Diagrammatic representation of lesponsive move-

ments in geotropically curved organs ... ... 679

258. Response of geotropically curved organ to external

stimulus ... ... ... ... 680

259. Effect of ether vapour on response of geotropically

curved organ ... ... ... ... 684

260. Death-spasm at the critical temperature ... 688

261. Death-spasm in the pulsating leaflet of Besmofliiim

ail vans ... ... ... ... ... 689

262. Electromotive and resist- vity variation at death

temperature ... ... ... ... 692

263. Death-spasm in the geotropically curved BaseUa aJha 693

264. Method of obtaining torsional response ... ... 696

265. Record of responses due to stimulation of the

different sub-petioles of Mimosa ... ... 698

266. The Electric Probe for localisation of the Nervous

tissue ... ... ... ... ... 701

267. Micro-photograph of a quadrant of petiole of

Mimosa ... ... ... ... 702

268. Galvanometric record of transmitted excitation in

different layers of Mimosa petiole ... ... 704

269. Curve showing intensities of transmitted excitation

in different layers of Mimosa petiole ... ... 705

xviii ILLUSTRATIONS

FIGURK. fAGE.

270. The course of nervous strands to the different

effectors in pulvinus of Mimofia ... ... 706

271. Diagrammatic representation of the posture of

leaves of Mimosa m normal and inverted position 711

272. Diagrammatic representation of the responses of the

four quadrants subjected to gravity ... ... 713

273. Records of responses of the right and left (luadrants

to stimulus of gravity ... ... ... 714

271. Photo-micrograi)h of transverse section of pulvinus

of X('j>fiiin(i phowing four quadrants. ... ... 716

275. Enlai'ged phot^-mici-ogi'aj)h of the lower quadrant

of .]fi)i)0';a ... ... ... 716

270. Photo-micrograph of transverse section of upper

side of geotropically curved / nijxif /'(».'< ... 718

277. Vertical and longituidinal section of upper and lower

sides of geotropically curved stem of ErJiptu ... 71&

278. Effect of feeble stiniiihis in enhaiuMng the rate of

growth ... ... ... ... ... 720

279. Effects of indirect and dii-ect stimulus on growth ... 721

280. Diagrammatic representation of a geotropic organ

in vertical and inclined jjositions ... ... 725

281. Diu hcliotropic adjustments of leaves in M/z/io-sa ... 734

282. Toisional response of petiole of Ileliauthvx in

response to photic and electric stimulus ... 740

■JsS. Diagi-am of stimulation of nerve-ending of

Helidfifhus ... ... .. 'j-^3

284. Galvanometric record of tiansmitted excitation in

nerve of JliliantJiiix ... ^^4^

285. Torsional response due to transmitted excitation in

Ileli'fnithiis ... ... ... 745

286. Method of obtaining electric response of the

pulvinus in Minioso ... ... ... 752

287. Uniform response of galvanometric negativity ... 755

288. Positive electric response in Miiiios^a, under feeble

stimulus ... ... ... 755

28!i. Resonant i-ecordcr for ueterniination of velocity of

transmission of excitation ... ... ... 759

290. Simultaneous mechanical and electrical iccords for

velocity of transmission ... 7g3

ILLUSTRATIONS XIX

FIGURE. PAGE.

291. Multiple electric responses undei; a single strong

stimulus (}f i/)io.s.i) ... ... ... 768

292. Multiple mechanical response in Mimosa under

strong stimulus ... ... ... ... 768

293. Effect of CO^, on autonomous mechanical pulsation

of Dtsinodiuvi ... .. ... ... 772

294. Effect of CO., on electric pulsations of Dcsmodmm 774

295. Transmitted death excitation giving rise to multiple

response in Averrlioa ... ... ... 780

296. Multiple response of leaflets of Biophytvm under

transmitted death-excitation due to poisoning ... 784

297. A stretch of Water-Hyacinth near Sijbaria on the

Ganges ... ... ... ... ... 787

298. Determination of the death-point of the Water-

Hyacinth ... ... ... ... 789

299. Photograph of the root of Water-Hyacinth ... 790

300. Effect of poison applied to the root of Hyacinth ... 792

301. Photographs of Chnjaavtheminn, in water and in a

solution poison ... ... ... ... 793

302. Effect of poison applied to the upper parts of the

shoot in Hijariiith and Chrysanthemum ... 794

.303. Diagram of experimentn,! arrangement for obtaining

resistivity response to mechanical stimulus ... 798

304. Uniform responses of the mechanically stimulated

stem by resistivity variation ... ... ... 799

305. Effect of chloroform in inducing depression of

response ... .. ... ... 802

306. The spark record of response ... ... ... 803

307. Method of resistivity variation for respons3 to

electric stimulus ... ... ... 806

308. Effect of stimulus of moderate intensity ... ... 809

309. Effect of sub-minimal stimulus ... ... 809

310. Multiple responses due to strong electric and

thermal shocks ... ... ... ... 810

311. Effect of CO. 2 in depressing response by resistivity

variation ... ... ... ... 811

312. Effect of dilute ether vapour ... ... ... 812

313. The Quadrant Method for determination of resisti-

vity variation ... ... ... ... 815

X\ ILLrSTRATlONS

FlGURi:. PAGE.
S14. Equal responses in opposite direetions by alternate

illuminations of the two pairs of quadrants ... 816

31.0. Response to light from a single spark ... ... 817

316. Effects of stimulus of light increasing in the ratio

of 1 : 3: 5 : 7 ... ... ... ... 817

317. I'^ffect of carbonic acid gas on response to ligtit ... 818

318. Effect of chloroform ... ... ... 819

319. Diagram of the Self-Recording Radiograph ... 828

320. Radiographs of variation of intensity of light of a

bright and a cloudy day ... ... ... 831

321. Record of diurnal variacion of light and temperature 832

322. Diagrammatic representation of a vegetable photo-

electric cell ... ... ... ... 837

323. Normal electromotive response in a vigorous

specimen ... ... ... ... 839

324. Abnormal positive response in a very young

specimen ... ... ... ... 839

325. Abnormal positive response in a very old specimen 839

326. Effects of increasing durations of exposures of light 840

327. After-effects of light ... ... ... 841

L]I.— ON ELECTRIC LOCALISATION OF THE

GEO-PERCEPTIVE LAYER.

By Sir J. C. Bose,

Assisted by

Satyendra Chandra Guha, m.sc.

Ill the second volume of tiie Transactions of the
Institute (1919), a very sensitive electric method is
described for the determination of the exact position of the
sensitive layer in the interior by which the plant is enabled
to perceive the vertical direction, so that the shoot or the
petiole places its length parallel to the. direction of the lines
of force of gravity, with the apex upwards. This directive
movement is accomplished by a responsive curvature, the
upper side becoming concave and the lower convex. The
concavity of the upper side is brought about by an excitatory
contraction, which I have shown .takes place under all forms
of stimulation, mechanical, electrical, chemical and
photic. It has also been shown that the characteristic signs
of excitation — diminution of turgor, contraction, and
diminution of the rate of growth — may be detected electric-
ally by an induced change of galvanometric negativitj^ If
suitable electric connections are made so that one contact is
on one side of the stem, and the other on a distant indifferent
point, then on laying the plant horizontal, the upper side of
the stem is found to exhibit an electric change of galvano-
metric negativity indicative of excitation. The geotropic
irritation and the electric sign of excitation disappears as soon
as the plant is restored to the normal vertical position.

('.(»(•

LIFE MOVEMENTS IN PLANTC

The seat of geotropic iti-itation is at ilie iHTceplive layer
itself: lieiice tlie electi'ic fcsponsc <>[ the perceptive layer is
the iiiaxiniiiiii p()ssil)li'. 1 have thus heen able to localise
the geo-perceptive layer by means of the I'.lcctiic I'lohc. fully
deserihed in the previous volnme ; the piiiiciplc of the nicthod
will he understood from the folhnving description : —

As every side of a radial oi'gan is geotropically cxcitahle,
the geo-pei'ceptive cells must i)e disposed in a cviindrical

l-'l(.. --\ I )i:ii;'i';tii]iij:it ic i'c|(n's(.'Ul ;il inn nf i he l:i'ii-|ici-c('|i| i\ c la\i-r
ill llic mu'Xfitt'd viTt ii-;il, siiul in cxcilcd liiiri/.(j|it;il |pii>il ion,

layer at some nnknown depth from the sm-face. whicli in a
longitudinal section of the shoot anoiiM appear as two
straight lines (I and (1, ('Fig. '221). In a vertical position,
the geo-perceptive layer will remain unaffected, but rotation
through 00° would initiate the excitatory reaction. Tjet us
first centre our attention to the geo-perceptive layer G, which
occii[)ies the upper position. This sensitive layer perceives
the stimulus, and is, therefore, the focus of in-ita-
tion : the state of excitation is. as we have seen, detected by
induced galvanometric negativity, and the electric change
would be most intense at the percejitive layer itself. The
excitation of the perceptive layer will iiradiate iido the
neighbouring cells in radial directions with dinu'nishin'j

hOCAIJSATION OF GEO-PKl{(i;i"rJ VE LAYER (101

intensity. Hence tlie intensity of the responsive electric
change will decline in both diiections, ontwards and inwards.
The distribution of the excitatory change, initiated at
the perceptive layer and irradiated in radial directions, is
represented by the depth of the shading, the darkest shadow
being on the perceptive la3-er. Had excitation been attended
with ^he change of light into shade, we would have witnessed
the spectacle of a deep shadow (vanishing towards tlie edge)

ki»»»» 'T

Fid. 222 Tlic KU'c7ric Prohe. Fiuuri' to tin- lott rc'inofiit s mw clcctiic
contact made with sepal of yijin i>li<if<i. and tlic otiiei', with tbc
flower stalk l>y means of the prolic : tin- iiicliulerl ir.ilvaiiometer is
represented In- a circle. Figure to tljc liglit is an cnlarg-ed view
of the jirobe.

spreading over different layers of cells during displacement
of the organ from the vertical to the horizontal ; the shadow
would have disappeared on the restoration of the organ to
the vertical position.

Different shades of excitation in different layers are,
however, capable of discrimination by means of the Electric
Probe, insulated except at the tip, which is gradually pushed
into the stem from outside (Fig. 2-22). It will at first
encounter increasing excitatory change during its approach
to the perceptive layer, where the irritation would be at its
maximum. The indicating galvanometer in connection
with the Probe will thus indicate increasing galvanometric

()02 IJFi; MOVEMENTS IN PLANTS

negativity, wliich will reach a niaxiimim value when the
probe reaches the })erceptive layer. After this, as the Probe
passes beyond the perceptive layer, the electric indication of
excitation would undergo decline and final abolition. The
characteristic effects described above are to be found only
under the action of gravitational stimulus ; they will be
absent when the organ is held in a vertical position and thus
freed from geotropic excitation.

The electric investigations with the Probe on the lines
indicated above enabled me to map out the induced electric
variation inside an organ under the stimulus of gravity.
The induced galvaiiometric negativity of the upper side of
the stem (indicative of excitation) is found to undergo
variation at different depths, and attains a maximuui value at
a definite layer, bejond which there is a decline. The geo-
perce])tive layer is thus experimentalh' localised by
measuring the depth of the intrusion of the Probe for the
maximum galvanometric negativity.

The electric response of the lower side of the organ to
gravitational stiunilus is, however, of an opposite sign to
that of tlie upper side, a (j alv an o metric positivity indicative
of expansion and increase of turgor. The electric indication
on the lower side also exhibits variations in different layers,
the maximum positivity occurring at the perceptive layer.
These responsive electric variations indicate that the layers
of tissue contiguous to the upper perceptive layer undergo a
contraction, while those contiguous to the lower perceptive
layer show an expansion.

In certain lower animals it has been found that the
weight of the heavy particles acting on a sensitive layer causes
the perception of the direction of gravity. From histolo-
gical considerations Haberlandt and Nemec came to the
conclusion that the heavy particles, such as starch grains,
performed a similar function in many plants. The electro-
physiological investigation which I undertook was for the

LOCALISATION OF GEO-PERCEPTIVK LAYER 60H

exact localisation of the sensory, cells i)i situ, and in a
condition of uonnal living activity. I also wished to record
the entire cycle of reaction, from the onset of geotropic
stimulus to its cessation in the living plant. j\Iy physiolo-
gical investigations fully confirm the conclusion that it is the
starch sheath " containing a number of large-sized starch
grains which is the geo-perceptive organ.

The experiments were first carried out with two

P=<s«»3a@:XXX>200o(?COOOoa300C©0=^^

FIG 225

^IG. 224

Fig. 223 Curve of geo-electric excitation in different layers of Nt/uqihaea.
Ordinate represents geo-electric excitation ; abscissa, distance from
upper surface of flower stalk. Diagrammatic section underneatli
shows the position of the geo-perceptive layer (starch-sheath)
cori'esponding to maximum induced galvanometric negativity ami
positivity on the two sides.
Fig. 224- The curve of creo-electric excitation ii\ different layers
of Bvijophythnii .

different species of plant, the flower stalk of NyinpJiaea
and the stem of BryophyUum. The curves obtained from
results of numerous experiments show that the maximum
electric reaction takes place in the particular layer which
contains the starch grains (Figs. 223, 224). As regards the

(')04 I.iri: MOVKMENTS JN J'LANTS

,i:e(^-t'lcctiic ic.ict ions it was loiiiul that tlie I'esponse is strong
at tlic particular season, wlien tlic pli\ siolo^^ical vij^oiif of the
plant is at its height : later in th(^ season, the response
nndtM'goes a rapid <leeline and final abolition. ^licroscopic
exannnation icvealed the cause of this difference. In the
lavourahle season, the starch grains in the sheatli are present
in gieat ahinidance : hut they disappear later. The presence
of starch gl•ain^^ thus appears to he associated witli the
sensitive I'eaction ol' the perceptive layer.

In addition to the effect of seasonal variation, there is
an additional factor, namely the intinence of normal varia-
tion of t(^i]iperatnre on geotropic response ; it ^vas found
that while the response was vigorous on cold days of
Calcntta M'inter (average temperature 20°C.^, it dechned
rapidly on the return of warmer days. It tints appeared
that within a moderate range of variation, a rise of tempera-
ture depresses geotropic action, while a fall of temperature
accentuates it. This found independent su])port from my
investigations on the diurnal up and do^^ll movements of
organs suhjected to the action of gravity. The "" Praying
J^alm "' of Faridpore is a striking exaniple of this. The
tree which grew at an inclination to the vertical was suhjected
to the action of gravity. Tlie maxinnim geotropic reaction
causing the highest enn-tion of the apex of the tree, was
found to take place at about 0 a.m. when the temjierature
was at its nnninnmi. The maximum fall of the tree, caused
by diminished geotro[)ic action, occuired at about '■] v.^\.
when the temperature was at its maxinnnn. 1 have showti
fm-ther that this thermo-geotropic reaction ex[ilains the
(hurnal movements of leaves of many plants.*

As regards the <>ff(^ct of tempiM-atnre on geotro})ic
res})onse, 1 found once more that while the gi^o-electric
response was ver\ pKiiked in the colder months of Ftdiruary

* Life Moxcniciits of Plants — Vols. T and If.

T.OCALISATJON OF GKO-PKRCKPTIX F. LAYER M't

(teiiij)eratiire -lO^i'.), it disappeared by the middle of A|)ril
wlieii the avera^;e temperature was about 30°('. With
TropacoliDu niajm I could get no response even in March.
1 afterwards renewed my experiments with this plant three
mouths later at the Mayapuri ]\esearch Station at Darjee-
Wu'j:. I was considerably surprised to find that the geo-
electrie resj)onse of the plant which had disaj)peared in
Calcutta in ^Nfarch was fully vigorous in May and June at
the hill station ; the temueratui'e at Darjeeling was lower
than •2()°('. This shows that geo-electric response is
accentuated, within limits, b}' a fall of temperature and
.in<l de[)ressed by a rise of temperature.

I have recently (19'21) been able to renew the investi-
gations on the localisation of the geo-perceptive layer in a
large nuiid^er of plants, the results of whicli are given
below.

GEO-Kr.HCTRIC RESPONSE OF THE PETIOLE OF TROPAEOLUM.

Detailed results of experiments on the localisation of
the geo-perceptive layer in the petiole of the Tropaeolum, are
given below as typical of the reaction in other plants.
Tropaeolum has the following special advantages. Geo-
tropically it is very sensitive ; its latent period of response
is very short, the horizontally laid petiole begiiming to bend
upwards in the course of a few^ minutes. The leaf may be
isolated from the plant, and the cut end of the petiole placed
in moist cotton. The normal geotropic irritability of the
cut specimen is found to be fully restored in the course of
half an hour. The manipulation of a cut specimen,
alternatelv in a vertical or in a horizontal position,
presents no difficulty. A very large number of
specimens is, moreover, obtained from the same plant. As
regai-ds geo-electric reaction of the petiole of Tropaeolum.

606 LIFE MOVE^rENTS IN i>LANTS

the induced electromotive variation is cojisiderahle and
attains the maximum vahie within a short time; tlie recovery
is practically complete after restoration to the vertical.

Tlie mode of experimental procedure is as follows; the
Probe is thrust into the petiole by successive steps of 0.05
mm. and the electric response observed on displacement of
the petiole from the vertical to the horizontal position, in
which latter case the organ is subjected to geotropic irrita-
tion. The induced electric variation, as already stated, is
of considerable intensity. The irritation caused by the
prick of the Probe is slight, since the fine Probe insinuates
itself into the tissue, rather than makes an\' marked ru})ture.
The immediate effect of the insertion of the Probe is a
negative deflection of the galvanometer, which declines and
practically disappears in the course of about 5 minutes.
The geotropic irritability moreover is fully restored in the
course of less than lo minutes, after which records of
geotropic response are obtained by photographic method.

LOCALISATION OF .GEO-1'EKCEPTIVE LAYKi; IN THF PETIOLE Ob

TROPAEOLLM.

Geo-electric excitation at different iayers. — I give below

the photographic records of responses to the stimulus of

of gravity at various lavers as the Probe was

Kxpcrimeiit 2;?0 . " • , ■ • p

thrust in irom outsule by successive steps oi
0.0-5 mm. ('Fig. •225). It will be seen that the geo-electric
respon.se underwent a continuous increase till the maximum
excitation occurred at a dei)th of 0.20 mni. A rapid decline
occurred beyond this ])oint and the response disappeared at
a depth of 0.50 mm. The following table gives the
quantitative results of the experiment.

LOCALISATION OF GEO-PERCEPTIVE LAYER

007

Fig. 225 Intensity of Geo-electric response at different depths in tlie

petiole of Tropaeoluni.
Xote the maximum excitation at a depth of 0.20 mm.

T.ABLE XLVII. — .SHOWIXG GEO-TROPIC REACTION AT DIFFERENT LAYERS

IN THE PETIOLE OF Tropaeolum.

Distance from

i
Geo-electric response of !

surface in mm.

galvanometric negativ^ity

0.00

5 divisions

0.05

9

0.1

LS „ 1

0.15

29 . !

0.20

42 „ i

0.25

20

0.30

11

0.35

7

0.40

5 „ :

0.4-5

2

0.50

0

Position of the

.starch sheath at

1
a depth of 0.20 mm.

Subsequent microscopic section showed the maximally
excited la.ver at a depth of 0.20 mm. was the sheath which

'"••'<'*> i.ii-'i'', .M»)\ i:mi:ni's in plan'J'S

i'>mI;mii('(I lilt' starch uiniiis. Tlic j^eo-percejitive laver is

thus loiind lo coincide with th(> stai'ch sheatli.

Maximum excitability of the geo-perceptive layer. —
'I'hc iiiaxiiiiiiiii excitation iiiihiced at th(> ))eicej)ti\(' la\er
appears to l)c (hie to two factors; we have first tlie direct
-^limiilation caused hy the fall of the starcli j2,rains ; secondly
Die (jcncrdl (■.rcif(iJ)ilil n of th«^ geo-perceptive layer is greater
tliaii that of tli(^ iicighhoufing ones. As regards the
relatively greatec excitahility ol' tlie })ei'ceplive layer, this
h(>caiiie e\i(leiit Iroiii the elTects ohserved diu'ing thi> |)assage
of the Prohe with the speciiiuMi ludd vertical. The inser-
tion of the I'rohe then acts as a iiiecliam'cal stiintdus, and
tlie res|)()nse hy gal\ anoinetric negativity is lomid to he
niaxiniuin at tlie starcli sheath, proving that this is relatively
the most excital)l(\ 'This jtaiticular response takes place
duriiui tlit^ thrust of the Trohe ; the resulting irritation
disa|)j)ears. liowever, when the Probe is left in a stationary
condition. The normal excitahility of the cells is restored,
after a period of rest of about Id iiiinutes. The geo-electric
response is ()l)served after restoration of \\\o normal (Excit-
ability.

A lew words may he said about the relative position of
the maximally excited laxcr. as found from the readings of
the Probe and siil)se(|uent determination of the position of
the starch sheath by microscopic examination of the trans-
verse s(M-tion. in \\\c example given above, th(> two are
found to be identical. There is, however, the possibility of a
sliuhl \ariatioii: the I'robe. as already stated, is inserted by
steps of 0.05 mm., and may, therefore, in the successive steps
of its passage He slightl\" on on(> or the otluM- side of the
sensitive laver. The error introduced from this is, however,
slight. .\s i-egai'ds the inicroiiietric deterini iiat ions, tbr"
section at the line of the ])assage of the I'robe should be
slightK moistened lor microsco|)ic examination: h)r too

LOCALISATION OF GEO-PKRCEPTIVK I^AYEn (109

loii^ Mil iiiiiiu'i'sioii ill wiitor is linhle, to cjmse a swelling of
the cells, and thus vitiate tiie ineiisiirements.

The following table gives the resuUs obtained with
twelve different spec-iinens of tlie petiole of Tropaeoliu)i.
The specimens were unequally thick"; hence the sensitive
litvei" was found at ;i depth of 0.1.") mm. in thin, and at
0.20 mm. in tliick specimens; the maximum electric excita-
tion was in all cases found to occur at the starch sheath.

TAELE XLVIII. — GEO-ELKCTRIC RESPONSE AT VARIOUS DEPTHS IN
DIfFEREXT SPECIMENS (PETIOLE OF T ropaeohrm) .

Re>

poiisive

galvMuoineti i\' ii

\uaiiviT_\

at depths of:

Xo. of

Position
of starc'li

S]>eci-
ineii.

_•

=■

=

c

5

5

£

slipatli
from

r

_

12

o

IC

o

CO

o
-*

surface

c

^

-

d

c

d

d

1.

T'lns.

IHiliis.

SOfliis.

35 (Ins.

2odiis.

0. fins.

0. dns.

016nnn.

•>

10 „

L'4 ,.

-IT „

84 „

H.J ,.

•"»7 „

7 „

0-20 „

8.

0 ..

♦ > ..

10 .,

25.,

s ,,

2

0 „

0-20 ..

4.

5 ,,

3.") „

57.,

:w .,

Ht ..

lo !,'

0 „

015 ,.

5.

H ,.

lo .,

'2.'2 .,

30.,

•24 ..

I-"> „

0 „

018 ,.

H.

o „

N ,.

15..

H .,

4 ..

1 „

0 „

015 ..

7.

3 „

■J ..

14,.

•") .,

•i ..

0 ..

0 .,

01 o ..

s.

0 „

]fi ,.

■\\ ..

48..

14 ..

12 „

.s ..

0-22 „

9.

3 „

12 „

15 ..

11 „

N .,

H .,

0 ,.

015 ,.

10.

2 „

10 ..

22,.

7 .,

;-i ..

1 „

0 ..

015 „

IL

3 „

IS ..

•.VI ..

43 ..

•Ar> ..

•SA ..

7 „

0-21 .,

VI.

0 „

'1

•> ,,

26 ,,

1 ••

3 ,,

0 „

0-20 .,

DECLINE OF GEO-ELECTRIC EXCITATIOX OX TWO SIDES OF THE
PERCEPTIVE LAYER

The experimental localisation of the perceptive layer is
greatly facilitated by the abrupt enhancement of excitation
at the layer. This will be fully realised from the resultant
curve obtained from data derived from twelve different
specimens. We take the ])erceptive layer it.self as the point
of reference, and measure successive distances .say of 0.05
mm. to the left and to the right of The point of reference.

010 LIFE MOVEMENTS IN PLANTS

The abscissa to tli3 left is towards the centre, that to the
right, towards the surface. Tlie mean vahies of the excita-
tory action at the different points are the ordinates for the
const riK-tion of the curve. It will be seen how abruptly it

Fig 22(> Curve t>li(>«iiii;' i/io-i'li'ct ric (listrihiitioii.
Maximum cxcitatidii (k-ciu's at <;o()-perceptiv(>
layer (). Excitatdrv ri-actioii ia|ii(lly decliiiesi
iii\vard.< and outwards (See Text).

rises to tlie uiaxiinmn at the perceptixe layer' and falls
beyond it inwards .ind outwai'ds (Fiy. •2-16).

GEO-ELE{.'TKIC EXCITATION AT THI-: UNDER SIDE.

The experiments with NyniplirKd and llniopliyJluni*
brought out the striking fact that under the stimulus of
gravity the excitatory electric reaction at the lower side is
of opposite sign <^o that at the upper side, a positive, instead
of a negative electric variation, the maxinunn positivity
occuring at the starch sheath. Since the galvanometric
negativity is associated with contraction and galvanometric
positivity with expansion, the geotropic ciuvalnre of the

* Life Movements of Plants— Vol. II.

LOCALISATION OF GKO-PERCEPTIVE LAYER (511

Stem or the petiole is thus due to the joint effect of contrac-
tion of the upper and exiiansion of the lower side.

GEO-ELECTRIC RESPONSE AT THE LOWER SIDE OF PETIOLE OF

TROPAEOLUM.

The account of an experiment on the electric response

induced at the lower side under the action of gravity is given

helow. The galvanometric response of the

Kxperiifieiit 2;32 . -, , , „ ,. . . .,

epidermal layer was +6 divisions. At
a depth of 0.05 mm. it increased to +15, at 0.1 to

Fig 227 Iiitciisiry of geo-electric excitation at
different depths at tlie underside of petiole of
Tropaeolum. Maxinmm excitation attained at a depth
of 0.15 mm. which is the starch-containing layer.

Note electro-positivity of response indicated by
down-curve.

+ 26 divisions. At a depth of 0.15 mm. the response attained
its maximum value of +40 divisions. It declined beyond
that layer to +11 divisions at a depth of 0.20 mm., and to
+ 2 at 0.25 mm. The geo-electric response disappeared at
a depth of 0.30 mm. The geo-electric distribution is thus
similar to that at the upper side, the characteristic difference
being in the change of the sign of the response from negativv^
to positive (Fig. 227).

()12 lAl'E MOVii.MllN'l S IN I'l.ANTS

OEO-Pi:i5CEl'TIVE LAVKI; IX I HI': SIEM OK Ti;()l'AEO].U]\r.

Tlie next investigation was underlaken with the stem of
'I'ropaeohi))! , which is also sensitive to geotropic action.
'J'hree specimens \V(Me chosei-: of ;.pproximntely the same

Ku; 22S < tc"o-i'lcct n'c l-csponst' ;il (litVciciit
(leiJtli.s ill the stem of 'rropiHMiluin. Mnxi-
iiiuin ivsiioiisc !it :i <li'i)tli ofO.K) nun. Avliit-li
conriiincd 1 lie stiircli-sliciil li.

thickness, and the geo-pcrceplivo layer locahsed by means of
tlie JYobe.

]n the first of these tlie response by galvanometric
negativity was 5 divisions at the epidermis, which increased
to 15 divisions at a depth of 0.05 mm. and tO
~ "" ;J7 at 0.10 mm. This was the climax,
for the response underwent a ra]>id diminntion
and abolition as the Probe passed further into the stem
(Fig. 228). Microscopic section showed that the layer at a
depth of 0.10 mm., which gave the maximum geo-electric
response, was Ihe one which contained the stanch grains.

LOCALISATION OF GKO-rERCKPTIVK LAYEP.

c.j;;

Siiiiilar results were ()l)taiiu'(l with- two other specuneiis.
The results are given in cK'tail in the lollowing tahle.

TABLE XLIX. — LOCALISATION 01 GEO-I'EIICEPTI VE LAYEK IX STEM 01

Tropaeolnm.

z

lU'.sp()iiise of yjil\aii()iiu>trii- iic,i;;H i\ it y ;il (lc|illis uf:

Distance

of stiircli

.shciitli

from

siu-fac(.'

0

1

0"05 uini. 01 null. O'lomni.

1 1

0'2 mm.

0'2o mm.

1

li
til

1

o (Ins.

.0 ;;

10 diis.
IH „
22

37 (Ins.
35 ,.
58 ,.

19 diis.
l-i „

7 dnh:.
2

9 ',!

0 dns.

0 »
ti „

OH) Mini.

on ,.

010 „ .

Localisation of Geo-perceptive layer in other plants. —
1'he geo-perceptive layer of a large number of other plants
was similarh* localised, by the Probe, a short account of
which is given below.

Cditniichjna. — The geotropic sensibility uf the stem of
this plant is shown by its erectile movement from a Jiori-
zontal to a vertical position. The geo-electric response at
the surface was 0. At 0.1 nmi. it was G, which increased to
a maximum of 18 at a depth of 0.-2. After this the response
underwent a rapid decline. The maximally excited layer
was subsequently found to contain the starch grains.

Myosotis. — The stem of Forget-me-not also gave strong
geo-electric response, the maximum excitation occuring at
a depth of 0.20 mm. In the microscoj)ic section the starch
containing layer was also found at the depth of 0.20 nun.
Ccntaurea. — The flower stalk of corn-fiower was found
tii exhibit electric response of moderate intensity under the
stimulus of gravity. It is sensitive before the opening the
flower buds, but this disappears later after the opening of
the flower. The maximally excited layer was at a depth of
0.3 mm., which also contained the starch grains.

Tifjer Lily. — The flower bud of this plant is strongly
geotropic. It gave the maximum geo-electric response at

t'l 1 4 LIFE MOVEMENTS IN PLANTS

a depth oi 0.3 mm. The starch grains occurred very near
this layer.

Convolvulus. — This gave the iiiaxiinuni geo-electric
lespoiise at a distance of 0.3 mm. from the surface, and the
starch layer was found at a depth of 0.28 mm.

The table given below embodies the above results, and
also those previously obtained with BnjophyUu))t and in
Nyiupliaea. Though the maximal excitation occurs at
unequal depths in different species of plants, the maximally
excited layer is always found to coincide with the starch-
sheath.

TABLE L. — GKO-ELECTRIC RESPONSE AT VARIOUS DEITHS IX DIFFERENT
PLANTS.

Galvaiioiiietrii

negativity at depths in mm.

Position of

S])('ciiii('ii

starch
sheath at
depth of :

0.

1

1

2 3

1

■4, 5

1

•6 -7

1

■«

]-4

IH

Coimiielvna

0

6

J 2

0

0-21 mm.

Myosotis

15

27

so' 31

7

o

0

0-3 .,

Centaurea

0

10

22 40

8

7

0

0-3 „

Tiger Lilv

7

11

2.5 54

7

o

3

0-3 „

Convolvulus

0

3

13 33

20 .5

0

0-2S ..

Brvo]tlivllum

0

24

4.5[

63

21

3

0

OH ..

Nymphaea

10

26

40

50

H2

1G8

72

1-4 ..

Tropaeolum (stem)

37

7 0

1

010 ..

,, (})etiole)

0

«

25 2

0

'

0-20 ..

The numerous experiments carried out with different
plants thus show, that the maximum excitation occurs at a
definite layer, and that this particular layer contains the
falling starch grains.

DUPLICATION OF GEO-PEHCEPTIVE LAYER.

The experiments described above brought out the
definite fact that during the passage of the Probe from the
surface to the central pith it encounters a particular starch
layer, at which the geo-electric response is at its maximum.

LOCAI.ISXTION OK (IHO-J'ERCKl'I'l VK I.AYKR «■.!')

I'roni this it iiii^lit at lirst af)peur. that the geo-perceptive
layer must always be sinj^le. There is liowever, an interest-
inp variation which is described below.

While experinientinji" with a specimen of plant wliich
was supplied from a nursery as the Cape Marigold (Calendula
stellataV), 1 was at first grcatlv ])n/zled bv
the tact that tins plant exhibited two dehnite
electric maxima during the j)assage of tlie Probe from the
siH'face to the pith. Thus in a given specimen, while geo-
electric response of galvanometric negativity at a depth of
0.1 mm. \\as 6() divisions, it increased abruptl}' to 115
divisions at 0.2 mm., and declined to 15, at the greater depth
of 0.30 mm. The response continued to decline till a depth
of 0.60 was reached, w^hen tlie response exhibited a second
maximum, this time of 10.") divisions. Below this the
excitatory reaction underwent a decline and abolition.
Detailed results are given in the following table.

TAKLK LI. — SHOWIXG DTJPLICATIOX OF GEO-PERCEPTI VE LAYER.

Distami" from surface.

( !<'o-flectri<' response

Siirf:ici- 0 nnti.

0 10 irini.
0-20 ,.
0-30 .,
0-40 ..
()•.■)() ..
OHO ..
0-70 ..

10 divisions

HO
115

1.-.

14

14
105

12

The two starch-sheatbs oecurred at depths of 017 and 0-58 mm.

Similar duplication of geo-electric maximum was also
obtained in a second specimen of the same plant. After
cutting section of the plant it was a matter of agreeable
surprise to find that there were two definite starch layers
separated from each other by a distance of about 0.4 mm ;

616 LIFE MOVEMENTS IN PLANTS

it was at these starch-sheaths that the maximum excitations
were ohserved. In the first specimen, the maximum
excitation occurred, as we liave seen, at a depth of 0/2 mm.
The microscopic section sliowed the first starch-sheath to be
at a depth of 0.17 mm. Corresponding to the second
electric maximum at 0.60 mm. there w^as the second starch-
sheath at a depth of O.o8 mm. In the second specimen, the
positions of the electric maxirna and the starch-slieaths

Fig. 229 Curve showiiii;: (liijilicatioii of treo-
f'lcctrk- maximum (.«ec Text).

exactly coincided, the first at a depth of 0.30 mm. and the
second at 0.70 mm. The curve given above (Fig. 2-29)
illustrates the geo-electric distribution at different layers and
the occurrence of the two electric maxima.

The above results afford another striking demonstration
of the fact that the layer which contains the starch grains
becomes the focus of inil;ition when the organ is displaced
from the vertical to the horizontal position, and that in cases
of two distinct starch layers, there are two foci of irritation
which coiiicid*- with the two lavers.

LOCALISATION OF GEO-PERCEPTIVB LAYER T)!?

Another significant fact was noticed in regard to the
geo-electric response of Calendula (?) that the geo-electric
excitability was very marked at the beginning of its proper
season, the sensitiveness disappearing later. Microscopic
section showed that this insensitive condition was associated
with the disappearance of the starch grains in the two
layers. Of these the starch grains in the layer near the
centre were the first to become reabsorbed.

THE EFFECT OF AGE ON GEO-ELECTRIC RESPONSE.

In connection with this, several interesting results were
obtained. While working with the peduncles of several
flowers it was noticed that a very strong geo-electric response
occurred before the opening of the flower, but the response
declined after the opening. Again, in the petiole of Tro-
■paeoJiDii, while moderately young specimens exhibited a
marked response, very young and very old specimens
exhibited little or none. The following investigation was
undertaken to obtain more definite results in regard to the
effect of age on geo-electric excitability. The uncertainty
arising from the employment of different plants was elimi-
nated by determining the excitatory action in different
members of an identical plant ; variation of age was secured
by choosing different leaves of the same Tropaeohim, the
leaf near the apex being the youngest, while those lower
down were of increasing age. I chose for my experiments
the second, the fourth, and the seventh leaves, counting
from the apex. The Probe was thrust in till the petiole
gave the maximum geo-electric response at an inclination
of 90° to the vertical.

In a particular series of experiments the second leaf

gave the maximum response of 4 mm ; the

response of the fourth leaf showed a great

enhancement, of 26 mm. ; the response of the 7th was found

ill 8 LIFE MOVKMRNTS IN PLANTS

to liave declined to 7 nun. In the table given below I give
the results obtained in three other series of experiments.

TABLE Lll. — EFFECT OF AGE ON GEO-ELECTRIC RESPONSE.

SeijiK'iii'c of loaves

.Ma.Tininni Negative electric response

Series I

Series TI

.Series 11]

Mean

Secoiii] pet inic
Fourth „
S«>veiit)i ..

4 IllTll.

H

\2 irini.

■.y.i „

17 iiiiri.

■■M .,
5 ..

1 1 intii.
■.i2 ..

It is thus seen that the geo-electric sensibility is but
feeble in very y<-)iing and old s[)eciniens.

SUMMARY.

The ge()-|)erce|)tivc hiyer, in the iiiinicious speciincns
examined, was found to coincide with the starch-sheath.

The geo-electric; response is diminished at high tem-
p('ratui-('s. The I'esponse wliich was found abolished in
-^Miiiiiici- ill tlir plains was loinid to juTsisi in the colder
cliiiiatt' of t lie hill station.

Ill cprtain plants, tlip geo-electric distribution exhibits
two maxima. 'J'he focus of irritation is not single but
double. Microscopic section showed that the starch-sheath
in these is not single but double, and that the positions of
the two »'lectiic maxima coiiicicU^ with those of the two
starch-sheaths.

(reotropic irritability is modified by age; it is strong in
the middle-aged, and feeble in very young and old
specimens.

TJII. THE EELATION BETWEEN THE ANGLE OF

INCLINATION AND THE GEO-ELECTKIC

EXCITATION.

By Sir J. C. Bose,

Assisted by

Satyendra Chandra Guha, m.sc.

If the pressiiie of lieavv particles on the sensitive
eetoj)l;ismic layer of tlie cell he tiie efficient cause of stinnila-
tioii under "ravity, it would follow that the irritation caused
by them will increase with the angle of inclination. In the
vertical position there would be no effective stimulus ; it would
be most intense at an inclination of 90°. The effective
pressure and the residting stimulation will evidently vary
as the sine of the angle of inclination to the vertical. The
theory of the pressure of the particles being the efficient
■cause of geotropic action w'ill thus find strong support if it
could be shown that the induced irritation varies as the sine
•of the angle of inclination.

As regards the measurement of the induced irritation,
it is theoretically possible to determine it from the mechani-
■cal or the electric response at various inclinations. But the
practical difficulties in the measurement of the mechanical
response are so numerous that it is impossible to obtain w^th
it any accurate result. No such difficulty is encountered in
the electric determination, the relative advantages of which
are as follows : in tlie mechanical response the induced
curvature is brought about by the modification of the normal
rate of growth, which takes place a considerable time after
the perception of the stimulus; the latent period of the
meclianical response may thus be as long as an hour ; the
rate of res{)onsive curvature is moreover indefinite, being
slucjgish at the beginning, rapid in the middle, and slow

»>20 LIFE MOVEMENTS IN PLANTS

towards the end, when the organ becomes nearly vertical.
Again the method of reversal, by which many som'ces of
error are eliminated, cannot conveniently be applied with
mechanical response. With the electric response, on the
other hand, the above difficulties are practically absent.
The latent period is very short and the maximum excitatory
reaction is attained in tlie course of a minute or so. The
excitatory reaction of galvanometric negativity disappears
on the return of the specimen to a vertical position. Again,,
the errors caused by the inaccurate reading of the angular
scale and the physiological asymmetry of the organ may be
eliminated by the Method of Reversal. When the plant is
inclined to the right through +90°, the current of

P(-

'

a

1

i

f7\

Fig. 2;}0 Diagraimnatic representation oF the <ren. electric
response of the Shoot.

response flows in one direction ; when it is inclined to the
left through -90°, the resjjonsive current becomes reversed;
the experimental error of a single determination is elimina-
ted by taking the mean of the two galvanometric deflections.
The details of the procedure will be understood from the
diagram given in Fig. 230. The specimen is first vertical,
with the two symmetrical contacts at the two sides, the
electrodes being connected in the usual manner with the
indicating galvanometer ; after inclination through +90°
the upper side A, becomes galvanometrically negative (right
hand figure). The excitatory reaction at the upper side finds
mechanical expression by the contraction and concavity,
with positive up-curvature. The differential excitations of

ANGLE OF INCLINATION AND GEO-ELECTIUC EXCITATION r.21

A and B and the resulting electric response disappear on
the return of the specimen to the vertical or zero position.
The specimen is next inclined to - 90° ; A now hecomes
the under, and B the upper and the excited side (left hand
figure'. The electro-uiotive change now undergoes a
reversal, B becoming galvanoraetrically negative. The
induced electromotive variation thus obtained is of consider-
able intensity, often exceeding 15 millivolts.

We shall now describe the experimental results on the
relation between the angle of inclination and the resulting
geo-electric excitation.

Excitatory Reaction at 45° and 00°. — In thiKS
investigation the tirst difficulty encountered is the
accurate determination of the angle of inclination. An
index is attached to the plant, and a stationary circular scale
enables us to find the angle through which the plant is in-
clined to the vertical. ]^ut the vertical or zero reading
itself is subject to an error of a few degrees ; this is accen-
tuated by the fact that we have no means of knowing
whether the perceptive layer inside the plant is exactly
parrallel to the surface of the stem or the petiole. The only
means of eliminating the error is by obtaining two
responses, say at + 45° and - 45°, by the Method of Reversal ;
in the first the index reading is +45° subject to the correc-
tion E, which is the error of the setting of the index. Now
this error will make the actual angle 45° + E and 45° - E
in the two readings for inclinations to the right and the left,
i.e., the angle will be greater in one case and correspondingly
smaller in the other. Hence the mean of the two responses
obtained through successive positive and negative inclina-
tions of the specimen will reduce or eliminate not only this
error, but also that due to the physiological asymmetry.

I give below a series of galvanometric responses of the

petiole of TropaeoJuyn, when carried through

xperiment _.>. ^^^^ entire cycle of inclination from the vertical

to + 45° (as read bv the movement of the index") , back to zero,

(i'22 \.\VK .MC»\'K.MF,.\ l.s IN |'I,ANT.S

and then to -45*^, and back once more to zero. The same
procednre was followed in the case of inclination to 90° ; the
records are given in Fig. 231. The response to +45° is
seen in an np-ciirxf. with siil)sc(|iieiit cccover}' on retnrn to
the vertical. IncUnation to - 45° gave a reverse response
of down-ciHve with siihse(|U('nt i-ecover\ . The amplitnde
of two responses are 10 and 17 (li\isi()ns respectively, the
mean being 18 divisions, hulinations to -90° and -00°

Kk;. 2'M Alti'rir.itc ircd-i'loctrir res[i<.ii:^t> :it + -i't" mid
+r,», also at 4 W"!ti.il W.

g;i\(' rise respectivelx to the two responses of 21 divisions
;,,i,| ;;(! divisions, tli.- ni.'an being 27 dixision-. The ratio
of the excitations at 00 and 15 is therefore 27 : Is or 1 : 1.5.
'V\w relation of sin 00° : Mti i:.° is 1 : I. 11. The ratio ..t
excitatorv actions at the two angles may thus he ?-egarded as
ai)|)ro\iniately the >anie as between the >ine-, of llu' angles

of inehnat ion.

The follow nig end.odies the r.-^ults (.f the observed
actions at 15° and 00° in six dilTerenl specimens of the
pel iole of '\'Ti>\i(tr<>l\nn .

ANGLF OF INCLINATION AND GEO-ELECTRIC EXCITATION 62li

TABr.K I.Iir. — EXCITATORY ACTIONS FOR INCLIiTATIONS OK 45'> AND
90". (I'KTIOLK OK T roimeolinn).

No.

Klectric respon.«p

h

Kiitio —

(a) f(.r 4.->" i (h) for W"

1.
4.

;{" divisinns
2S
1!'-

:5T

n.") (livisjioris
40
274

;^2

44

1-488
1 -428
1 -42tS
1 ■4."i4
1-420

1-4:^2

.Mean i-:itiiic)t' cxciliil ioii . . ... 1 '44
Ratio of siiieti ... ... .. 141

The mean ratio of excitatory actions at the two angles
i.'; 1.44 while the ratio of the sines is 1.41. It will be noted
that there is a persistent .small difference between the two
ratios, the ex(-itation at the larger angle being greater than
the value deduced from the ratio of the sines. The relatively
greater excitation at the larger angle may have a physiolo-
gical significance of which reference will be made later.

Excitatory Reactions at 45°, 60°, and 90°.— The

relative excitatorv actions with a different

batch of petioles of Tropaeolum, was next

obtained for the three angles of inclination of 45°, 60°, and

90°.

TABF.K LIV. — EXCITATORY ACTION AT ANGLES OF INCLINATION OF 45'^.

AND 90" (Petiole of Tropaeolum).

Klectric response at

No.

I

1 (:.) 4.-,°

(b) 60»

(r)

90'-'

1.

; :{M (In.-.

49 (Ins.

54

fins.

j :{2

40
40

47
4t>

4.

.,.,

29

34

.-,.

14 ..

19

25

K.

1 iv«

22

2.5

Mean

2H

:«

38

Ratio of

excitations

1 :

1-26 :

1-47

„

sines

1 :

1-22 :

1-41

♦ ".24 LIFE MOVEMENTS IN PLANTS

The determinations given above show once more that
the excitation is but approximately proportional to the sines
of the" angles of inclination, the ratio of excitations at larger
angles being relatively greater. The next series of observa-
tions were with angles of inclination whicli increased bv
steps of 10° degrees.

I took ])hotographic records of the responses at the
successive angles of inclination of 45°, 55°,

Experiinont 237

()5°, 75° and 90°, which are re})r()duc-ed in

Fi(i. '2'.i2 KiH-ords of trcD-electn'c res]K>iis('s at various aiifrles.

Figure 232. The table gives the detailed results.

TABLE LV. — GEO-ELECTRIC RESPONSES AT INCLINATIONS OF

4.0,° F)r,° er..* 75° A\n ;t(i^

Angles

45"

5.5"

H5''

75" j HO"

Responses

44 (Ins.

52 fins. 57 <lnp.

HI dns. 68 dns.

Katio of excitations ... ... 180 l^S : l-*;^!

sinoR ... ... 1-28 \m : 141*

ANGLE OF INCLINATION AND GEO-ELECTRIC EXCITATION G25

Further experiments were carried out with twelve
different specimens of petiole of Tropaeolum

Experiment 2'd>^

and the mean excitatory action at the different

angles are given in the following table :

TABLE LVI. — GEO-ELECTRIC EXCITATIONS AT VARIOUS ANGLES.

Angles

45"

55"

65"

75"

90"

Responses

40'8 dns.

47 dns.

55 dns.

605 dns.

633 dns.

Ratio of excitations
sines

1 : VIH
1 : 115

: r34 : 1-48 : 155
r2S : \-M] : 141

The ratio of excitations, compared with the ratio of
sines is thus seen to undergo a gradual increase with
increasing angles of inclination. Thus to take the two
extreme cases, the divergence between the two at 55° is 2.6
per cent, whereas at 90°, it is 9 per cent. This definite
divergence which is persistent in all the determinations
points to certain physiological difference.

In attempting to find an explanation of the relatively
greater excitation at larger angles of inclination we have to
take account of two different factors, first of the pressure
exerted by the particles, and second the irritability of the
ectoplasmic layer pressed by the particles. As regards the
first, the effective pressure exerted by the particles is pro-
portional to the sine of the angle of inclination. As
regards the irritability of the ectoplasmic layer, this may not
be the same throughout the length of the cell but greater
towards the apical end. At the smaller angle of inclination,
say to the right, the statoliths, originally at the base of the
cell, accumulate to the right hand corner of the cell; a
portion of the basal side of the cell is thus subjected to
pressure. When the angle of inclination is increased, the

•'-'• I.II'I'. MoVl'.MKNI S IN I'l.ANTS

Statoliths pass alon^ the whole l»Mi<,^th of the cell, iiiclmliri':
the apical end. 'I'he relatively «,^reater excitation with iii-
creasin<i aii<ile of iiiclinalioii may therefore be explained on
the assumption iliat the cxcitahiiity of the ectoplasm is
greater towards the apex. We shall next consider facts
which app(>ar to lend support to thi^ view.

I'.XCII \ rolIY \("I'loNS AT 4-")° AM) \:\')°.

A controversy has arisen in regard to the
fpiestion as to wheth(M- the intensity of geotropic
excitation is the same or dilTcrcnt at tli(> angles
of inclination of 4o° and l.').")°. The effectixe pressure
exerted by the particles are the same at tlie two angles ; the
•only difference in the two cases is in the collectioti of tlie
particles at the basal end at 1-')° and at the apical end at 185°.
Czapek has found that the effective stimuhis of gravitation
is greater wIumi the organ is held at l.'i.")^ tlian wlien held at
45°. though his results have not been ac-cepted by others. In
mv woik' on I 'lout HcspoHsc dDOGi experiments have been
described on geotropic response at 45° and 1.'i5°. 'The
specimen employed was the unopened flower of Crhiuni
lily, the response being mechanical. The results showed
that the response to geotro[)ic stinndus at 185° is greater
than at 45°.

1 have recent l\ carried out further (experiments on this
sid)ject employing the independent method of
electric response which is more reliar>le and
accni'ate than the method of mechanical res{)onse.
Allowance was made for anv possible change in the excit-
ability brought on b\ fatigue. This was secured
by carrying out the expeiiments in the following sequence
of obserxation (1» of response for 15°. cit of response
for l.")5° and '8* of response once more at 15°. The com-
parison of the first and the third responses would show

ANGLE OF INCLINATION AND GEO-Bm.CTRIC EXCITATION (127

whether any change in the excitabihty had occurred on
account of t'atigiie ; allowance for this is made by taking the
mean of the two responses for 4o° at the beginning and at
the end of the series.

Geo-electric response at 45° and 135°. — Observations
with the petiole of Tropaeolnm were made as
follows ; the tirst and the third responses for
450 -^ere found to be 47 and 4o nun. respectively, tlie mean
of the two being 46 nun. The second or intermediate
response, taken for ^'^■^>° gave 55 mm. The excitatory

Experinient ■J4<i

Fk;. 2;?;3 Geo-eleetrio respoTise
ill sequence ot" 4.)", 1:^5'' uiid 4.")".

actions at 45° and L'j5° are thus seen to be in the proportion
of 46: r)'), or as 1 : 1 .-J. In a second series with a different
specimen the first ami the third responses at 45° were both
25 mm. (Fig. 233). There was in this case no fatigue.
The intermediate response at 135° was 31 uuu. The ratio
of the excitatory effects at the two angles are tluis in the
proportion of 25; 31 or as 1 : 1.2. The excitation at 135°
is thus about 20 per cent, greater tliau at 45°.

»)2fS LIFE MOVEMENTS IN PLANTS

Experiments were next carried out with the stem of Con-
volvulus ; at 45° the excitatory deflection was 26 divisions ;
when the angle was increased to 135°, the deflection was
enhanced to 31 divisions. That the excitation at 135° was
greater than at 45° was evidenced in a convincing manner
by the return of the angle to 45° when the galvanometric
spot of light was immediately restored almost to the first
deflection ; tiiere was a slight fatigue and the deflection was
25 divisions instead of the former value of 26 divisions. The
ratio of the two excitations at 45° and 135° is thus 25.5 : 31
or 1: 1.23. In a second experiment the two excitatory
deflections W'ere as 18 : 21 or 1 : 1.31 ; the mean ratio from
the two experiments is 1 : 1.27. The various results that
have been given all tend to show that the excitation is greater
at 135° than at 45°.

TABLE LVII. — GEO-ELECTRIC ACTIONS AT 45" AND 135>',

Specimen

Electric response at

1

45"

1 35"

45"

Tropiieoluni
C(>iiv(>lviilu>

47 dns.
25 ,.
2() ,.
16 ..

55 dns.
31 .,
31 ,.
20 .,

45 dns. 1
25 ., !
25 ..
16 ..

Ratio of excitations at 1 ;-{5" and 4.5" Tropaeolum 1 : li'
,, ,, ,, ,. Convolvulus 1 ; 1 27

We found from \\\v indications of the experiments
already described m regard to the effect. =; of the angle increas-
ing from 45° to 90°, that excitation is relatively enhanced
with the increase of the angle. The relative effects at 45°
and 135° may therefore be taken as extension of that
generahsation. It would thus appear that the ectoplasmic

ANGLE OF INCLINATION AND GEO-ELECTRIC EXCITATION 629

layer is not uniforinly irritable at all points, but that it
undergoes a variation, the apical being more excitable than
the basal end.

(lEOTROPIC ACTIONS AT THE UPPER AND LOWER SIDES OF THE
HORIZONTALLY LAID ORGAN.

We shall next consider the very difficult problem
relating to the geotropic curvature of a shoot or a
petiole. The upward curvature could only be due to the
differential actions at the upper and the lower sides of the
organ, otherwise the antagonistic effects at the opposite sides
would neutralise each other. The responsive up-curvature is
only possible (1) if the contractile effect at the upper side
is greater than at the lower side, or (2) if the effects on the
two sides are of opposite signs, namely, a contraction at the
upper and an expansion at the lower side ; in this latter case
the two effects would be concordant. The investigations
with the Electric Probe already described, indicate that the
physiological effects induced at the upper and lower sides are
of opposite signs, a galvanometric negativity indicative of
contraction at the upper, and a galvanometric positivity
indicative of expansion, at the lower side. The physiologi-
cal actions are thus concordant in bringing about the up-
ward geotropic curvature of the stem or the petiole.

These opposite actions at the upper and lower sides
being thus established, we are confronted with the further
difficulty of finding an explanation for this characteristic
difference. The solution of this problem will be given in a
subsequent chapter.

SUMMARY.

The geotropic excitation is found to vary approximately
with the sine of the angle of inclination.

CM) LIFE movkmf-:nts in plants

The results of niunerons expeiiinents tend to show that
the excitatory reaction ;it increased angle of inchnation is
relatively greater than t})e value deduced from the law of
sines.

This enlunicenient may he explained on the supposition
that the excitability of tlie ectoplasmic layer at the apical
end of tlie geo-jierc-eptive cells is greater than at the basal
end.

Tliis consideration linds supj)ort from the fact tliat the
geo-electric excitation at 135° is about l.'i times greater
than at 45°. In the first case, the starch giains acctmiulate
at the basal, and in tlie latter case, at the apical end.

The geotropic up-curvature is only possible by a
differential reaction at the upper and the lower sides of a
horizontally laid stem or petiole. Electric investigations
show that the tissue contiguous to the upper perceptive layer
undergoes contraction, while that contiguous to the lower
perceptive layer undergoes expansion.

LIV. THE ClilTICAL ANGLE EOE GEO-ELECTlilO
EXCITATION.

By
Sin J. C. BosE, 4

Assisted by
Satyendka Chandra Guha, m.sc.

A new line of investigation will be described in
the present chapter which will afford an independent,
and crucial test as regards the falling" starch grains being the-
effective factor in geotropic excitation. The results, to be
present]}' described, will be better understood if we visualise
the process of the fall of the starch grains in consequence of
the inclination of the organ to the vertical. Let us take a
mechanical model in which a layer of sand particles are
resting on a fiat surface. On gradually increasing the
inclination of the surface to the horizon, there will at first be
no displacement of the particles ; for on account of friction
and cohesion they will remain sticking against the
surface. During the continuous increase of the angle, a
point will be reached when there will be an abrupt sliding"
dow^n of the particles.

This angle of sliding we shall designate as the critical'
angle ; it will be relatively high if the surface be rough, and
low when the surface is smooth. Again a rough surface
may be smoothed down by the repeated sliding down of the
particles. The critical point may thus be lowered by
repetition of the sliding process.

1)."^2 UFE MOVEMENTS IN PLANTS

Tjct US further imagine the flat surface to be bounded
b}; vertical walls. The lateral pressure of the particles will
be slight and constant at the two sides. P)nt after inclina-
tion above the critical angle, the fiill of tli(> jiarticles and tlie
resulting incrcas(> of j)ressui'e on one side will be ver^'
abrupt.

The mechanical model d(>sciihed ai)o\c may be taken
as rej)resenting the statolithic cell. If the geotropic
stinuihis be brought about by the falling stai'cb grains we
should ex]HH-t that :

(1) Tlie i)articles will not be displaced at small angles
of inclination and there would thus be no excitation.

{'2) On gi'adually increasing the angle of inclination, the
particlt^s will slide down and press against the side of tlie
cell, as soon as tht^ critical angle is exceeded. This abrupt
fall of j)articles and the resulting increase of pressure will
constitute a stinmlus and give rise to an excitatory response.
(M) Repetition of the process is liktdy lo lower the
critical angle to a certain extent.

Ml }lad th(^ weight of the fluid coiitents of the <-ell in
higliei' plants been the only means of stinndation by gravity,
the excitator\ reactions would have been proportional to the
sines of the angles of inclination above zei'o. But there
would i)e a hiatus in this relation, if the hdl of the solid
Darticles be the efficient cause. There will be no excitatorv
response at angles lower than the critical. ]\ven at a
slightlv greater angle than the critical, some of the jiarticles
mav remain sticking at the base, and the excitation wouh'
be (lispro|)ortionately lower than what is demanded by the
law of sines. It is onlv after the critical angle has been
con-^iderablv exceeded llial the ri'lation of sines will be found
to hold good, at least ap))roximately.

We shall now subject tlie above theor(>tical consideratioTis
lo the test of experiment. We shall lirst attempt to

CRITICAL ANGLE FOR GEO-ELECfRIC EXCITATION iV.VA

discover if there he any (Hscoiuiiuiity in the responsive
reactions at angles helow 4-")^, aI)ove which they have
been found approximately proportional to the sines of the
angles of inclination. After discovering this break of con-
tinuity we shall attempt to discover the critical angle
and its exact value in (litrei-(MiT species of plants.

EXCITATORY ACTIONS AT 35°, 45°, AND 60°.

From the results of experiments detailed in the previous
chapter it is found that the geo-electric excitation is approx-
imately pro])ortional to the sines of the angle of inclination.
In order to observe whether the relation holds good at lower
angles, a series of observation were made with six different
specimens of the petiole of Tropaeoluui at 35°, 45°, and 60°.
The results are given in the following i"able.

T.\BLE LVIII. — GEO-ELECTRIC EXCITATIONS AT 35°, 45° AND 60°.

Si)ecinien

Electric Response

35"

4.0"

60^'

1 1

HI diis.

39 dns.

49 (Ins.

2

I'.t

32 .,

40

3

7

31 ..

40 ..

4

7

22

29 ,.

.")

6

14 ..

19 ..

r,

5

19 ..

22

Mean

103

20 1

33 1

From tlie above we find that by increasing the angle
above 45° the ratio of excitations at 60° to 45° is as 1.34 : 1,
■while the ratio of sines of 60° to 45° is as 1.22 : 1.

)),'U 1.1KI'. :movf,mf.x'is in plants

liy dwn (isniij the an^ile on the otlu-r liund we obtnin the
following : —

Eatio of excitation at 45° ami 85° is as 1 : 0.39.
,, ,, sines of 45° ,, 35° ,, ,, 1 : 0.81.

Ill order to ;i\()i(l (leciiiiuls we limit i|tly tlu^ ii!)ove ratios
by 1(10 iind ol)l;iin tlic I'ollowing results.

35° 15° r,o°

Excitations 39 100 134

Sines 81 100 122

The dotted tlnii curve given in Figure 234
represents the sines of the various angles of inclination ; the

23 30 ZS 40 4S SO SS 60

V\i...'l'.S\ Climes sli(i\\ iliL;- \;iliu> nf sines (iIhIIimI) ;iIi(I (if
e.\citati(iii.s (thick Jiiie). Tlio lalter iirodiirod cut.'s al».sc-i!S.s:i at
yi'.j", indicating al)sciicc of oxcilatioii at a critii-aj aufflc. Oi-di-
natc i\'|>rcsi'iits i-xcitat imi, aliscissa tlu' aiiL;lc nl' inclinai inn .

continuous line represents the excitations at the correspond-
ing angles. It will he noticed that while the divergence
between the sines and the excitations is slight above
45°, it is ver} jn-onounced at the lower angle of 35°:

CRI'l'ICAI, AXCLK FOIJ ( ; KlVI-'J.I'X'Ti; IC I'.XCIT ATION u'M'f

it indicates the approach of sonic liiatus or di-^-
-continiiily. By producing tlic cuivc hiukwards we find it
to cnt the abscissa at 81..-)° at wln'cli angle the excitation
■would be reduced to zero. This is the critical point ; aboxe
this angle the excitatory reaction will be abrupt.

We shall next investigate whether such a critical ]><)int
actually exists as foreshadowed by the curve and by the
theoretical considerations detailed at the beginning of the
chapter.

DETERMINATION OF THE CRITICAL ANGLE.

The discovery of the critical angle was the out-
come of my investigations on the geo-electric response
of NympJiaca (1919). The electric response was
being recorded by inclining the sjiecimen from th'3
vertical to the horizontal. This was done very graduallv
in order to avoid any mechanical disturbance likeh' to dis-
arrange the electric contacts. There was at first no indica-
tion of geo-electric excitation as the angle was gradually
increased from zero upwards, and it was a matter of great
surprise to note the sudden excitation which occurred as the
inclination reached the approximate value of 33°. The
excitatory action was detected by the sudden deflection of
the hitherto quiescent galvanometer s^x^t of light. (^n
return to the vertical position the excitatoiy deflection dis-
appeared. A repetition of the experiment gave the same
result. As the excitatory action was due to the fall of the
starch grains, it was clear that these particles had remained
sticking at the base of the cell till they were precipitated
above the critical angle.

Further experiments A\itli \ ijiiiplnica had to be
abandoned for the year, as tlie [iroper season of the plant was
over. I have since been engaged in finding out whether a
critical point for geo-electric excitation could be detected in

(u\G LiFF. ;movkmknts in plants

other plants as was suniiised from the trend of the curve given
in Figure 'IM, i'roni wliicli critical point for the petiole of
TroiKicolii))! aj)pearc(l to he about 'M.-)°. It is very remark-
able that the critical point of \ !i)iij)li(i((i should be so near
the ai)ove value. The critical point of 'A-)'-' found for
Kipiijiliaca was very apjjroximate. The following experi-
ments were carried out for the determination of the critical
angle of ditTerent i)laiits, every precantioR being taken for
securin;^ tlu" highest accuracy.

Determination of the Critical point for the petiole of
Tropaeolum. — I shall tir^t give a continuous

Kxi>i'riiini]i 211 ^' .

photographic rec-oi'd of tlu- electric response of
the ptetiole of Tro})(ic()]u})i as it \\as gradually inclined front

l'"iG. 2'3o. .Minipt Lri'o-olcctric-
response at an iiielination of 31"
(Trojiaortluin ),

'2-")° to .'U°. by successive steps of '2°. There was no response
at -2)°, 27° and 20°. When the angle was increased to
31° the response occurnMl al)ruj»tly. (Fig. 235). The
restoration to the vertical was attended by a recovery.

1 may dwell once more on the special advantages offered
bv the electric method in investigations on the excitatory

CRITKAI. ANCLK FOR CKO-KI.F.tTiMt' i:XCH ATION 637

action uiuler the stiinulus of j^ravity. The electric response
is ahnost instantaneous; as the angle is j^radualiy increased!
we ohtain an immediate effect at the critical point, indicat-
ing the moment when the particles begin to slide down. In
contrast with this are the difficulties inseparable from the
mei-hanical methotl which render any accurate determina-
tion a matter of im[)ossil)ility. For mechanical response,
which is at all a[)preciable, takes place after a considerable
length of time. The autonomous movement of the plant
whic-h must take [ihue during this interval, will obviously
produce a slow dis[)lacement of the particles downwards,,
even at an angle lower than the critical. These drawbacks
are absent in the electric determination, where the critical
angle at which tlie particles are abruptly precipitated be-
comes innuediately detected.

The possible error in the exact setting of tlie index at
zero of the scale is eliminated by the alternate inclination to
the right and to the left. The mean of tlie two effective
inclinations thus gives the true value of the critical angle.

Derailed accounts will now be given of determination of
the critical angle of the petiole of Tropaeohwi.

Experiment '242 i p • i • • • i

The angle of inclination to tlie right was gra-
dually increased and the hitherto quiescent spot of light
exhibited a .sudden deflection to the right at 30°. On return
to the vertical the excitatory action disappeared. Inclination
to the left gave a sudden deflection at -35°, the deflection
being now to the left. And nothing could be more striking
than the unerring certainty with which an invisible force
was evolved at definite points of alternate inclinations, which
gave a sudden push to the galvanometric indicator, now to
the right, then to the left. The mean of the two angles in
this experiment gives the true value of 3-2.5° for the critical
angle. The results of five observations are given iir
Table LIX. The mean of these determinations with six

€38 i.iFi', :\I()Vk:\ikn IS ix tlwis

tlifforent petioles of I'ropucohnit is rouml lo he 81.7°, wliicli
is in r(Mniirkal)le agi'et'iiiciit with the \\\\\\c of tlu^ critical
poiiit of Ml.r)0 as dednccMl IVom lli(> point where th(^ excita-
tion cnrve ci'osses th(> ahseissa (see Fii^". "284).

Determination of the Critical point for the stem of
Tropaeolum. — 'I'he ci-itical jiomt lor the stem
was ju'xt (letuniined, the proccnhire adopted
bein.i; the same as in the last ease. The niiniinnni angle
at which lh(> res))()nse occiirrtMl hy the right-handed rotation
was -1-33° : rotation in the left direction gave the response at
-30°. Hence the Irne critical angle for the specimen was

Rx])i'riiiuMii

:]].:

Ywe othei' detei'niinat ions were made with other

lv\|)criiiu'iM L' I I

specimens, and the i:i(-an critical angle ohtained was 3"2.7°,
wliich is ver\ iiearh the same as tli(> critical angl(^ Tor the
petiole.

Critical angle for the stem of Commelyna bengalensis.

With this plant an inchnatioii of 4-80° gave
the excitatoiy I'esponse ; inclination in tlie
opposite direction gave the response at -33°. TIk^ trne
<'i-itical angl{> is thus 31.')°. in a s(>cond specimen tlu^ mean
^•ahle of th(> critical angle was found to he 31°.

T.ABLK I, IX. — THE CRITICAL ANGLE FOR VARIOUS PLANTS.
SiiociliK'ii No.

Petiole of
Tropaeoliuii

Stem <.r
T'i'oi);ieo!inii

Stem of
Conimelvna

r

TI

Tir

IV

\'

VI

T

II
ill
IV

\'

VI

ir

Inclii
right

ation to
or left

Ciitical
iinirlc

]\rean

-!-;')a .

— ii;")

3-JT)

+ ;;(i .

— ;U-5

\vi-i:>

+ :;.T .

-:',o

3-iT,

:;i-7

+ 'j".i

-:52

:'.()•.'.

+ •_'.'.

—37

3 to

+ ;ii .

-;r2

.31 :>

-t-;53 .

—30

3f.-)

J- 1) -,

—30

;!2T)

-■:')(; .

—30

;;:')

?,TCy

"^ .'■> .

-3-2

:;3-.-)

+ :'.! .

—33

;i;'.")

+ ;•',:; .

—30

31 o

4 .'iO .

— ."»;')

31 T.

•:,V2L

+ :')"2

— :'.i 1

.•".1

CRITICAL ANnLE FOR GHO-ELECTIJIC EXCITATION i'>'.')9

The mean critical value for various plants examined is
thus 31.8, the maxiuumi variation from this is less than 1°
It is very i-emai-kal)le that the critical angle for different
plants observed should exhil)it so close an aoreement.

THE EFFECT OF REPETITION.

1 stated at the i)eginning that repetition of the experi-

mejit is likely to reduce the friction and
Exi>erim(_'iil 'J4."i , .i i- t i ^ -^i • ji

lower the slidmg" angle, and with it the

•critical point. It is very interesting to find that

this was found to be the case as regards critical angle for

geo-electric response. T took three different specimens of

the petiole of I'rdjKicdliiiii , the experiments being carried out

three times in succession. In every case it was found that

the effect of repetition was to produce a considerable lowering

of the critical point. In the first specimen the critical point

was lowered from 8i2.-')° to 28.5°, in the second from 31° to

■2-2.5°, and in the third from 30° to 22.5°. In Commehjna,

however, the diminution was slight, namely from 31.5° to

v50°. at the second rtMietition.

TAPLE LX. — THE EFFECT OF REPETITION ON THE CRITICAL ANGLE.

Specimen

i

Direction of inclination

1

Mean Critical
Anple

P.iL'ht

Left

1
Petiole of 1 .
Troi);ieoliim ' 2.

r :;.

2 (

.' ! . )

• ..;

?,'2-r>

?>]
2S-.',

!

' 1.

3.

■ ) r^
2'l

2^

:;i

2(;t,

2 -J-.",

1.
Ill -2.

2 It
24

2;,

27

22-:,

()-iO LIFK MOVKMKNTS IN I'LANTS

The experiments that have heen described offer the-
stron^e'-t eoiifirination of the statohthic theoi'v. It has
been siiown that the ^eo-eleetric excitation is procUiced when
the or^ian is held in a horizontal position. lUil when
the or^an is gradtiahy inclined from the vertical there-
is no excitation till the critical angU' is reached. The-
abrupt excitatory reaction must therefore \)(' due to the
siuUlen fall of heavy j)articles from the base to the side of
the cells.

SUMMARY.

The excitatory reaction imdcr stimulus of ,t;'ravity, isi-
reiluced disproportionately with diminution of an<iie of
inclination. This indicates the a|>jiroach of some hiatns or
discontinuity. l>y j)ro(bicinji the cur\e of excitation back-
wards, it cuts the abscissa at about •"U.-'i^ at \\liicli angle-
tlie immediate excitatory reaction would be I'educed to y.cvo.

The critical an.uie for ^eo-elect rie excitation has been
found in a large nund)er of ])lants to be atiout '■VI'^ .

The effect of repetition of inclination is found to lower
tlie critical angle.

The al)rupt excitation abo\e +he critical angle can only
be due to the sudden fall of the particles from the ])ase to
tlie side of the sensitive cells. The exj)eriments therefore-
offer the strongest support to the theory of statoliths.

LV.— EESEAECHES ON THE EFFECT OF
ANAESTHETICS ON GEOWTH.

BY

Sir J.C. Bose,

Assisted by

(Uruprasanna Das, l.m.s.

The effect of various anaestlietics on yeotropic curvature-
will be given in detail in the next chapter. Since the-
fundaniental mechanism of geotropic curvature is the
differential growth at the u})[)er an.d lower sides of the organ,
we shall in this chapter investigate the effect of various
pnaesthetics on growth itself.

The difficulty in investigations on longitudinal growth
arises from its excessive slow rate, on account of which a
long perioii elapses before any perceptible elongation
can be detected. But the prolongation of the period of
observation introduces other complicating factors such as the
variation of temperature and of light, which modify the
growth. These difficulties are overcome by the device of
the High ^Magnification Crescograph* in which a system of
compound levers produces a magnification which may be
raised to ten thousand times. Any change in tiie rate of
growth is thus immediately detected, the experiment being
completed in tlie course of a few minutes during which
external conditions could be maintained constant.

METHOD OF RECORD.

The specimen of plant, suitably mounted, is attached to
the first lever at a short distance from the fulcrum; the

* Life Movements in Plants, Vol. I., p. 152.

641

(J42 I.1FK :\iovK:^rF.\is tx plants

second or recordiiig lever produces a further magnification.

'Tlie totnl lunLinificatioii omployed in tlie following experi-

Fi(, L';it>. Ill,- lliiili .M:ii4Miiic;iti()n Crcsco,<>mph. Plant I\ iittaclunl to
tir.st lc\er : second U'vci' romnls .successive dots of lii-owtli-oloncjatioti on
smoked jrlass (J, kept oscillating- by clockwork C. Adjustment of lecordini^
point is made l>y makinjf |)lani move up oi' down by rack and in'nion H.
( Onc-foui'tli normal size.)

iiiciits is 1 (»(•(» tiiiios. (Fig. -286). The recording plate i.s
kept oscillating at intervals of 1o .-seconds, so that successive
dots give the tiine-record. The plate is also moved ir< a

EFFECT OF ANAKSTIIKTICS ()\ CRoW'llI {\-i'A

horizontal direction and tlu' nornial rate o[' j^fowtli and its
induced variation is lound from ilie recorded eurve.
Enhancement of growth causes an erection of the ciirNe and
also wider spacings between the successixe dots. Diniinn-
tion of the rate is shown l)y the flattening of the cnr\e and
the closeness of the dots : arrest of growth is indieated by
a horizontal record, and an actual contraction l)v the reversal
oi the curve downwards.

APPLICATION OF .\N.\ESTHETICS.

Mnch difficulty was at first ex[)erienced in tlevising an
effective method for subjecting the specimen of plant to the-

FiG 237 Chamber for a]i])lic;iti(iii of aiuic-i liotics i see Text".

action of anaesthetic acting" uniformly on all sides of the
organ. This was overcome by ihe following device in whicb

<">44 J.IFE MOVEMENTS IN PLANTS

a detachable cylinder acts as a cover ; it has a layer of thick
absorbant cloth lining the inside. The pill box cover which
closes the cylinder (with a hole tor the protrusion of the
specimen for attachment with the Crescograph) has a
circular tube soldered underneath, with a series of small
holes ; one end of the tube is provide^l \\ itli a liimicl into \\ liicli
]s poured :i given dose of ether or chloi'ofonu. The
anaesthetic drips down into the absorbing cloth and the
specimen soon becomes uniformly surrounded by vapour of
the anaesthetic (Fig. -237). As the plant slowly absorbs the
vapour, the immediate effect is due to a small dose; at the
second stage, the effect of a ' moderate ' dose makes its
appearance. And linally, the effect of an excessive dose is
found from the rec(jr<l at the tliii'd stage. The effects of
different doses of apj)lication are thus found in the course of
a few minutes by the i'ec(jrd given by an identical specimen.

EFEECT OF ETHEK ON (iROWINC, OR'.ANS.

The following may sei've as tyj,)ical examples of results
obtained from an extensive series of investigations
carried out with vai'ious organs of different plants; amonu
these may be mentioned the seedlings of AVheat ; the stems
ol HcliiDithus and of Daltlia ; the petiole of Tropaeolum; the
tendril of Cncurbita ; the penduncles of Hibiscus, of
Centaurca, of Daffodil and of Allium ; the flower bud of
Crinunt lily; and the pistil of Dutnrn. The I'csults obtained
are similar in all these cases; out of these, tbi'ee repi"esenta-
tive experiments will be described in detail.

Seecllin(jfi of ]]'lt((it. — The specimtMi \\as an intact

seedling with roots; it exhibited a fairly i-a))id rate of growth

as peen in the first })art of the record

(rig. •i.J.Sa*. On application ol ether the

growth-rate became very greatly enhanced in less than 15

seconds and jiersisted for a consideral)le leiigtli of time.

EFFECT OF ANAESTHETICS ON OROWTH 045

"This is seen in the erection of the curve and wider spacinps

between the successive dots. Continued aj)plication of

•ether caused a subsequent depression of the rate.

Crimi))t lily. — The resuh seen in this reiord is

.•similar to that obtained with the seedhng of Wheat. Tiie

acceleration occurred within 30 seconds of
Experiment 247 ■• ■ p ,

the application or ether vapour ; the

enhanced rate persisted for a period of 3 minutes, after which

Fig. 238 Effect of ether vapour ai)plied at arrow in enlunieiii'j: the
i^atc of growth in :

(a) Seeding of wheat ; (bj Crinum lily and (c) Stem of Helian-
thus. In this last, there is a renewal of arrested growth.

the depressing effect of a large dose is seen to occur as

illustrated by the response curve (b) tending to become

horizontal.

Ste})i of HeliantJiiis. — The cut specimen was found to

be in a state of arrested growth and the result obtained under

pther is of much interest. It shows that
Experiment 24S

etlier not only enhances the rate of existing

growth but brings about a reneicaJ of arrested groivth. In

bib \.\\-\: MOVKMKN'l'S IN PLAN'J'S

this case, tlic j^fow lli-rcnewal occurred within 9U seconds of
tlie application of ether \a[)oui- (curve c), the jj^rowtli.
persistin;^ lor a loni; time.

KFFI<X'r ()!'■ Clil.onot'ORM.

I'ctiolc (if I'rdiHicolitni. — 'I'he i)rehiuinary effect of

chloroform vapour is an acceleration of the rate of growth.

In the petiole of 'I' roiKicoUnii this accelera-
]v\)iuiiineiit '249 . i . • i- i

tion occurred i innnites alter llie

apphcation of the anaesthetic ;Mid persisted for a ])eriod of

i-'ic 2;j'.) luffoct of clilorofortii \ :i|Hiiir on L!]-n\\ 1 1] ; iicdril.s exhibit eiVocts
fliaractei'istic of throe stni^'cs, ;m onliniicciiKiit , ;i n ;iinsi. uiid ii sjuiisiiiodiL'
death -con tract ion.

((() I'etiok' of 7', ',/„„■<,////,( : ( 7/ ) I'cdiincK' (if ( V,//-//mt« : (r) Crlinnu
lihj and (tl) Pistil of Jhilinn.

4 minntes and 15 seconds ; this was followed by an arrest of
growtli for 45 seconds after which there was the abrnpt
coidractioii due to the dent h-sj);isiii (h^ig. -JMDiit.

. Penduuclc of Centaurea. — The specimen was in a state

of arrested growth, as seen from record (b) ; apphcation^

of chloroform vapour induced a vigorous

Kxiiciiineiit 2..0 i r- on i

growtli alter an interval of SO seconds.
Here also we obtain the. renewal of growth under a smalf

KKI-I'K T <t|- AWKSTHKTrCS ON CRfiWTH 647

dose of the anaesthetic. 'The ivxived growth persisted for
3 minutes, after which there was an arrest followed hv the
spasmodic death-contraction.

Crimint hhj. — 'LMic specinieii in this i-ase was also in a

state of arrested growth. Apphcation of chlorofoiiDi

renewed tlie growth in less thaji 30 seconds

Kx|)i riiiiciii J."> I

uiirxe (•). rnder the continued action of

chlorofonii the revived gi'owth which had persisted for 2

minutes am' 1 •') seconds was arrestetl : this was followed hy

a \ iolent spasmodic contraction.

Pistil of Ddtnid. — Having descrihed the effect of the

anaesthetic on peduncles and on flovver-huds I shah next

descrihe the response of the pistil. The
K.xiK'riiiifiit 2.')- IV /• 1 I •

eilect ol chlorotorni on normal growth w;is
a great enhancement which occurred iii the course of '.M>
seconds {curve d). This persisted for nearly 2 minutes after
which there was an arrest and subsequeiit spasmodic
contraction.

The growing organ undej" chloroform, tluis exhibits a
preliminary expansion followed hy contractioji. The con-
traction by itself should not be regarded as the sign of death,,
for we shall find later, that there are agents which induce
a temporary contraction from which a revival is possible.
The test of death-spasm is an irreversible change, from
which the plant cannot be revived by substituting fresh air
for the anaesthetic. This contraction under the prolonged
action of chloroform, (by which even the interior of the
tissue becomes affected) ma}' be taken as tlie death-s})asm..
since a renewal of fresh air in the plant chamber does not
bring about the revival of the plant. Another interesting
phenomenon observed after chloroforming the plant is the
profuse deposit of minute drops of liquids on the surface.
This is due to the forcing out of the sap during death-
contraction, the escape being facilitated by the increased

\\4X \AVK MOVKMHNTS IN PLANTS

permeability of the cells at death. Dark spots of dis-
coloration soon begin to appear, and spread rapidly over the
surface of the organ, which soon becomes wilted from the
loss of turgor.

As regards death-spasm under an anaesthetic, it is
instructive to compare with it the parallel effects of strong
■stinmlus of an electric shock. When this is very strong,
the response is i)y marked contraction of l)oth pulvinated
and growing organs. The plant is killed by the strong"
stimulus and there is no subsequent recovery. But if a
moderate stimulus be applied to a fresh specimen, the plant
will 1)0 fomid to recover from its excitatory contraction, and
respond once more to stimulus. The excitatory contraction
may thus pass from a reversible to an irreversible condition
of death. We shall find later that this is equally true of
the action of anaesthetics, a strong dose of which causes a
contraction and death ; but a mild dose of anaesthetic
induces, after a time, a contraction from which there is a
recoverv brought about bv substitution of fresh air.

SUMMAItY.

The various growing organs, the stem, the j^etiole, the
peduncle, the tiov;er-bud, and the pistil exhibit similar
reaction under a given anaesthetic.

A small dose of ether induces a great enhancement of
the rate of growth; arrested growth is revived by it. The
effect of a large dose, or of prolonged action, is to paralyse
growth ; timely substitution of fresh air is attended by a
revival.

The effect of continued action of chloroform vapour is
as follows : —

At the first stage there is produced a great acceleration
of growth, or a renewal of arrested growth; at the second

EFFECT OF ANAESTHETICS ON CROWTH <)49

stage the growth becomes arrested ; at the third, or final
stage there is a violent contraction.

As chloroform in large doses is toxic, its prolonged
application gives rise to the spasm of death. After
this the surface of the plant is found to be covered with
minute drops of liquid forced out from the plant during its
death-contraction, the escape being facilitated by the in-
creased permeability of the cells at death. After this, death
discoloration spreads out rapidly and the specimen becomes
wilted from loss of turgor.

LYi.— I'Hi: j-:ffi;('ts of anaesthetics on
(J EOT J ;op I ( ' 1 ; E sroN SI-:.

BY

Sii: J. (!. Bosk.

x\ssisted l)y

TjALTt Mohan IMukkimj. b.sc.

An iipvvaicl ^leotropic curvature takers place when the
growing stem, tlie peduncle, the petiole or the flower-hnd
is placed in a horizontal position. T^his is due to the con-
cordant effects of induced retardation of growth or contrac-
tion of the upper, and enhancement of the rate of growth and
expansion of the lower side of the organ. The co-ordinated
effects on the upper and the lower sides were independently
demonstrated by the results of electric investigations. The
upper side exhibits increasing galvanometric negativity,
characteristic of excitatory contraction ; the lower side
exhibits, on the other hand, an increasing galvanometric
positivity indicative of expansion and enhancement of the
rate of growth. In pulvinated organs, the upward geotropic
curvature is dije to diminution of turgor a?id contraction of
the upper, and enhanced turgor and expansion of the lower
side.

Besults of investigations by the electric method also
show that the geo-electric response occurs a short time after
the onset of the geotropic stimulus. But on account of the
sluggishness of growth and its induced variation, tlie
initiation of geotropic curvature becomes greatly delayed
This is accentuated bv another complicating factor, namely.

650

ANAESTHETICS ON (;iA»TU« )PIC HKSP0NSI5 OT* I

that of the weiglit, which causes a bending down of tlic
organ. The upper side of the organ is thus subjected to a,
tension and the lower siile to a compression. Tliis
differential action causes, at the beginning, a downward
curvature, which has to be reversed by the true geotiooic
action. The geotropic curvature is thus delayed, often i'or
more tlian an hour. The conipHcations described above are
serious obstacles for accurate determination of the geot topic
response and its induced variation. These difficulties have
been overcome (li In the choice of a specimen which is
quick in its response, and (-2) by reducing the weight of the
specimen h.y cutting off portions which are non-est^ntial.
These conditions are fidtilled hy the petiole of TropacoluDi.
The lamina is cut off, the weight of tiie short length of the
petiole being thus greatly leduced. The cut ends are
wrapped in moist cotton, and after a rest of half an hour the
irritability of the specimen is found to be fully restored.
Pinally, (3) the beginning of geotropic response can be easily
■detected l)y the employment of a magnifying lever. The
sensitiveness of the petiole of Tropaeolimi is, hoAvever, so
great that a magnification of five times is quite sufficient for
the purpose of record, which is taken on a plate oscillating
•once in three minutes, the successive dots representing that
interval of time.

This i^lant Tropacolmn grows in Calcutta during the
winter months froin November to January and during the
months of February and March which are the spring season ;
the plant begins to die off' hy the beginning of April. The
experiments described below were commenced in February
1920, and continued till March, 19*21. The experiments
were thus carried on during two springs and one winter ; the
records given by the spring and the winter specimens exhibit
certain differences whicli are characteristic. In the spring
epecimen, the latent period, or the period which elapses

652

I. IKK MOVEMKNTS IN PLANTS

i

between the a[)i'lioati()ii of tlic stinmliis of ;^ra\ity and tJie
commencenieiit of the geotropic up-moveiiient is six minutes
or less, after which the rate of movement hecomes uniform
for about half an hour. The slope of the curve, and the
distance between the successive dots indicate tlie geotropic
activity ; any induced enhancement of the normal rate is, as>
already explained, exhibited by the erection of the curve-

Fig. "2 jo. Geolropii' furve : (a) of a siiriiii,'', and (//) of a w inter
.specimen. The latent period of the former is si.\ minute.'^, of the
latter forty-eij^ht miTiutes.

Xote the relatively erect curve of the spriny specimen inditat-
inij a more intense u:ec)tropie action.

and greater separation of the successive dots; depression^
on the other hand, is indicated by the opposite change. In
the winter specimens, owing to the general depressed rate
of growth, the geotropic response is very sluggish, as seen
in the prolonged latent period, which in the particular
experiment is seen to be 4S minutes ; the sluggish character
of the response is also in<hcatcd by tlu' gentle slope of the
geotro[)ic curve (I'^'ig. '24(>>.

ANAKSTHI"riCS ON (iKOTHOPIC RESPONSE

Gf):?

The iiiiitoniiity of the erectile response cannot be
maintained tor an indefinitely lonj^' period, since any further
response is inipossil)le after tlie full erection of the specimen.
J I should therefore bo held a few degrees below the horizon,,
and record continued till it rises through the same angle-
above the horizontal position. The slope of the curve is-
tlien found to remain practically uniform for about half an
hour, which is more than sufficient for the completion of the
experiment on the action of the anaesthetic. Having
described the experimental method, we shall next study the
effect of ether on geotropic curvature of (A) pulvinated and
(B) of growing organs. The effect of chloroform will also
be studied in these two dilTerent types.

EFFECT OF ETHER (»N GEOTHOPIC CURV.ATURE OF PULVINATED-

ORGANS.

Mhiiosa. — The leaf of Mi))iofia, normally speaking.

FlfJ. 241 FIG. 242

Fig. 2-il. Effect of ether on geotropic respon.«e of the leaf of
-Vimosa.

Fig. 242. The geotropic response of tlie terminal leaflet of
Deamncliiim (itjrans under the action of ether.

assumes the so-called dia-geotropic position, which is
approximatelv horizontal. Enhancement of

E.xperinient 2o.S

geotropic action would cause an erection of
the leaf. Tn the experiment described below, the leaf on

<'.54 LIFK MOVrMKNItS IN IM.ANTS

aocoiint of its (liunuil inovcmcMl. was exliihitiii^ a Tall ;
application of ether \apoiir at tlie point marked with the
arrow arrested this fall ; afterwai'ds an erectile inoNciiK^nt
\\as iiiitiate<l wliicli iiidieated an enlia iieenuMit of ^^eotropic
action. Tliis occiwi'ed in the coiir.se of U) seconds, and the
erectile movement persisted lor a further period of 7 mimites
<Fi^. 241). Continued action of the anaesthetic was after-
wards found to arrest all fui'tliei' nio\enient.

'l\'ni\'ni(il hdjiet of ])esmodinni. — 'J'he leaflet was in a

stationary dia-i;eotiopic position. Applica-
Kx|i<M-inHiil 1'.-. t . , ", .

tion of ether vapom' induced in a short time,

a }4reat enliaiicenuMit in llie ^^eotiopic curvature as s(>en in
fi-ure •J4-2.

EKI-'KCT OF KTHEF? ON OEOTROPIC CUHVATURE OF CROWINf,

ORGANS.

petiole of Tropaeolum. — After the attainment of
iniiform ^cotropic; uj)-uiovement, a specimen

Kx(i<'riin('iii ■_'."i"> ,. ,,. 1 • 1 I

ol / roiKieoluiii \\as sul)jecte(i to the action
of ether vajjour ; this induced a very fjreat enhancement of
^eotropic movement in the course of 'A minutes, as seen in
the erection of the ciu've and in wider spacinjjfs of the
succes.sive dots (Fig. '243).

Having thus ohtained a definite proof of the enhance-
aneiit of the geotropic action under ether, two batches of

six similar petioles of 'iropapoluin were taken

Kxpi'rimciii L'oH i i ■ n ,• i \ n

and placed li(in/( »nta 1 1\ : ol these the ni'st

iKitch was placed in a cliauil)er containing air, the second

batch hein^ placed in a cliamhe'- which contained a smaM

<juantity of ether vapour. <>ii cxunuuing the two hatches

aftei' an lioiu'. it was found that while a slight curxattire was

produced in specimens undci' iioinial condition, those

^uhjectcd to the vapoiu' of ether had htjcome highly eret-te''

the tips being bent even backwards. The striking difl'erence

hetw«'en the two v\ill be xmui in the r<'productions from a

ANAI-SlHi: I us ON t.KOl H(ti'k' HI.SI'oNSK ♦).'").>

photograpli of the normal and the etherised specimen

Fk;. 243 F^ffeot ot'etlicr in eiihaiicfiiiciit ')f
;:eoti-i)j)ic response (Petiole of TiO[i(irfl n m .)

(Fig. 244). The experiments on piilvinated and on growing
organs thus exhibit similar results, namely, an enhancement

Fig 244. The effect of ether vapour on jjjeotropisni N, the normal action
in air; E, the effect in an atmosphere of ether vapour.

of geotropic action under moderate application of ether
vapour.

65() r-IFK MOVEMENTS IN PLANTS

EFFECT OF CHLOROFORM ON GEOTRvOPIC RESPONSE OF
PULVINATED OUGANS.

Mimosa. — The preliminary effect of chloroform vapour
is seen to induce, in the course of 80 seconds, a great enhance-

Ex])CM'iimMit 2.")7

nient of the geotropic action, as seen in the
rapid erectile movement ; this was arrested
in the course of three minutes after which tliere occurred a
very rapid contractile movement (Fig. 245).

Desmo(liu))i leaflet. — The leaflet was executing a slow

Fig. '245 ?;ffect of clilordforiii \a|i()iii- en iif()trc>i)ic res-
ponse of Miiiiiisd.

Note enhancement at the fiivst staye, arrest at the second,
and reversal at the third stage.

Fig. 24H Similar effect of chloroform on L;eotro])ic res-
))onse of the terminal leaflet of Dt'^unidiu m .

up-movement. Apphcation of chloi'ofoini iiuluccd jiicliini-
nary enhancement of ge()ti'Oj)ic action in tlie
coui-se of 40 seconds. This persisted for two

minutes and a half, after which tlu^ movemont undorwont

a reversal (Fig. 246).

Experiment 25S

EFFECT OF CHLOROFORM ON GFOTIioRIc i;KSPONSF OF GltoWING

ORGANS.

The following expcriinciits on tlic action of chloroform
were carried out with two ditTerent species of plants, the-
seedlings of Eclijifa rrrrta. ;ind the petiole of Tropaeohan^'

ANAESTHETICS ON GROTROPIC RESPONSE 057

with the object of brin^in^^ out certain characteristic
differences.

Seedling of EcHpta. — Tlie skhi of KcUpta is somewhat

impervious to vapour : hence a relatively small quantity

of chloroform vapour is absorbed by the

Experiment 25M m, , . «. •

plant. The characteristic effect is seen to
be a great enhancement of geotropic action which persisted
for a considerable length of time (Fig. 247a).

Petiole of Tropaeolum. — In the last experiment,

Fii;. 24" Effect of chloroform on geotropic response : (a) enhancement
of geotropic action in Acliptn, (b) preliminary enhancement followed by
arrest in Tropaeolum [See text].

absorption of small quantity of chloroform gave rise to
acceleration which is characteristic of the
first stage. In Tropaeolum, the petiole
absorbs the vapour more readily, and we observe an enhance-
ment of geotropic action at the first stage, and an arrest at
the second stage (Fig. 2476).

i'tbi^ l>IFIi MOVKMKNTS IN PLANTS

In reviewing the effect of inmestlietics on "eotropism in
growing" organs, we :iiv able to trace it to tlu> induced
modification ol' j^i'owtli itself. l'\)r ether has been shown to
enha.nce the rate ol growtli ; it also enhances the rate of
geotropic movement. ('hloroforni induces a preHminary
enhancement of ^lowth followi-d hy an anest. In geotropic
response under chlorofoitn we also obtain a preliminary
increase followed l)y arrest of geotropic movement. Effects
parallel to these are also obtain(Ml with jailvinated organs.

SUMMARY.

The geotropic action in growing organs is dependent

■on its growth-activity. In spring, the latent period is

relatively short aiul the rate of elect ilc nio\ement rapid.

In winter, the latent |)erio(l is |)rolonged and the geotropic

movement is sluggish.

J'jther induces an crdianix-nicnt of geotropic action both
in pulvinated and in giowing organs.

The effect of chloroform in a moderate dose, is an
■enhancement of geotropic action followed by an arrest.
Excessive application may, however, give rise to the reverst'd
^■on tractile movement.

LVII.— THE EFFECT OF CARBON DIOXIDI-: ON
GEOTROPIC ACTION.

BY

SiK J. ('. Bosk.

Assisted by
SuRENDRA Chandra Das, m.a.

In considering" the action of different anaesthetic agents
we found that the effect of chloroform is very intense and
ultimately fatal; ether is less toxic and does not, under
normal conditions, produce the death of the plant. The
effect at the first stage in both is the same, namely, an
enhancement of growth and of geotropic curvature. At the
second stage, we obtain a paralysis of sensibility, the geotropic
response being thereby arrested. Substitution of fresh air
often brings about a restoration and the renewal of geotropic
action. The effect of ether, generally speaking, stops at the
second stage : but with chloroform in excessive dose, the-
effect of the third stage makes its appearance — a spasmodic
contraction followed by the death of the organ.

Carbonic acid gas may be regarded as a mild narcotic, its
effect being comparable to that of ether. One wotild there-
fore expect, that its effect on geotropic response would be
similar to that of ether, that is to say, an enhancement of
response at the commencement followed by an arrest under
its continued action. The normal geotropic action might
also be expected to be restored on substitution of fresh air

659

■<)60

LIFE MOVEMENTS IN PLANTS

EFFECT OF CARBONIC ACID GAS ON GEOTROPIC RESPONSE OF
(iUOWING ORGANS.

Effect on winter specimens of Tropaeolum. — The

■results anticipated were liiUy xcriHed in all tlie experi-
ments carried out during tht winter season of 1920, of
which ih record is given in Figure 248a ;

Kx])(>riiiuMit 2til ■ , xi i • i e • i.i

owing to the sluggislmess ot response m the
■cold season, the latent period (tlie fir-^.t part of the record

Fii;. 24s KlTt't't i)i'{'() on Lrcotr()|)ii' ri'8]ii)nse of ^'/-i^iac'/'n/i :
((() Kffect on winter specimen ; CO. aijplied at arrow

induced i)relijninary enhancement followed by

arrest.
(/») Plffect on sprinjf specimen ; CO, apjilied at arrow

and fresh air substituted at circle. The effect

induced is a preliminary enhancement followed

by a reversal. Substitution of fresh air renewed

normal geotropic action.
('•) Enhancement of ireotropic )'es]ionse followed l)y

]>crsistent reversal under continued action of

the.iras.

not shown) was found to be 40 minutes. The geotropic
curvature was tlien initiated at a slow rate, as seen in the

CARBON DJOXIDE ON GEOTROPIC ACTION ("•tJl

slightly inclined curve of ascent. Carbonic acid gas was
next passed into the plant-chamber ; this caused a great
-enhancement of the geotropic action in the course of about
3 minutes. The induced enhancement is clearly seen in the
very erect curve, and in the separation of the successive dots ;
the acceleration persisted for 20 minutes, after which the
geotropic movement became arrested. This arrest was not
permanent, for introduction of fresh air was found to bring
about the subsequent renewal of geotropic up-movement.

Response of Spring Specimens. — The experiment with

the winter specimen is described at the beginning since its

res])onsive characteristics are easily explained.

Experiment 2H2 t, , „ . . " -,

J3Ut the response ot specmiens ui the earlier
months of the year, in the spring" of 1920, presented
peculiarities which appeared at first to be quite
inexplicable. This will be understood from the
records (Fig. 248'>>, in which the latent period is as short
as six minutes and the erect curve shows the con-
siderable geotropic sensibility of the spring specimen.
After the attainment of uniform erectile movement, carbonic
acid gas was made to fill up the plant-chamber ; this induced
a great enhancement of geotropic movement in the course
of 3 minutes, a result characteristic of the first stage. The
erectile movement was temporarily arrested in the course of
21 minutes. There next followed the astonishing, and at
first inexplicable, result of the reversal of normal geotropic
movement which carried the tip of the specimen heJow the
horizontal position. It thus appeared as if carbonic acid gas
caused a reversal of the normal geotropic response. Fresh
air was next introduced into the chamber, with the result
that the normal geotropic up-movement was renewed after
an interval of five minutes.

In another experiment, a stream of carbonic acid gas
was maintained throughout the experiment lasting for more

*'i(>2 I.llK. M()\ KMKN'IS IN l'i,\MS

than an hour. It gave the same sequence of eHet-ts as before,
namely, an enhancement at the first stage, a temporary arrest
at the second, and :i reversal at tlie third stage. The tip of
the specimen imdei- the continued action of gas persisted in
its reversed {)osition hiHow the horizon. The results given
above were so nne\|)ecte(l that 1 was at first inchned to
attribute it to some unknown and abnormal condition. But
repetition of the cxpei-iincnt a year later, in the spring of
19-21, fully corrol)<)rated the j)revioiis ohseixalions.

The results described above relate to the action of car-
bonic acid gas on the geotropic response of Tropaeolum. For
determination of the universality of the phenomenon, further
investigations were undertaken with a large numlier of
growing and pulvinated organs of different plants.

Response of the peduncle of Tube-rose. — Thi.«

specimen gave tlic normal geotropic ivsjjonse, though

the effects were relatively sluggish. The latent period was

4-") mimites. Contimied action of carbonic

Kxpcn'mciit 2H;!

gas induced a reversal of normal geotropic
response in the course of six minutes. On the substitution
of fresh air in the plant-chand)er, the normal up-movement
was once more initiated. Continued action of carbon
dioxide is thus seen to produce in the Tube-rose a reversal
of geotropic action similar to that in Tropdeoliou .

EFFECT OF CARIiONJC AC'ID C.VS ON (;E0TI!( UMC KKSPONSK
OF PUIA'IXATI'O ORC.ANS.

The geotropic excitability of the upper half of the
pulvinus of Mi)n<).'ia is very nnich less than that of the
lower half. Tt thus happens that the leaf of Mimosa is in
a state of equilibrium in a horizontal or the so-called
dia-geotropic position. But if the plant be inverted
so that the relatively more excitable lower half is above, the
geotropic excitation and the resulting curvature are greatly

CARBON DIOXIDE ON OKOTIiOPIC ACTION ('(GH

enhanced, the leaf bc'coinnij^' continuously erected in this
inverted position. Tlie experiment may be carried out
with a small piece of cut stem of Mimosa bearing the lateral
leaf; the sub-petioles may also be cut off, thus reducing the
weight of the petiole. In order to prevent drying, the cut;
ends of the stem and of the petiole are covered with small
pieces of moist cloth. The sensibility of the pulvinus is
fully restored in the course of an hour, when mechanical
stimulation is found to cause the normal fall of the petiole.*
The cut specimen may now be easily manipulated and held

"rfT

Fig. 249 Method of record of geotropic response of Miinoga, held in an
inverted position with the more excitable half of pulvinus B facing upwards.

in the inverted position (Fig. 249) for obtaining the normal-
record of geotropic up-movement, which is brought about
by the joint effects of contraction of the more excitable half
B, and the expansion of the less excitable half A.

Effect of CO 2 on G-eotropic Response of Mimosa. — The
first part of the record in Figure 250 shows the uniform
geotropic response in the inverted position. The plant-
chamber was next filled with carbon dioxide.
This caused an arrest, and a subsequent
reversal of geotropic response, which occurred 2 minutes after
the application of the gas. By this reversal, the leaf was
* Life Movements in Plants. — Vol. I., p. 81.

Experiment 264

<">♦'■! I IFK MOVKMKNIS IN ri.ANI S

broii^lit below its orij^iiiiil j)<)siti()ii and iiiaintain»>(l there.
Siibstitiition of IVesli air broii;^ht ;il)()iit a restoration, and
the normal ^eotroj)i(' response was renewed in the course of
four ininutes.

Kr\ithri)tn indicd.- -'V\\t' puKinns of l^njlliriiid is less

sensitive llian that of Miiiiosa : tlie cliaraoteristie effects are,

in other i'es))ects, the same in the two cases.

ilie cut specimen was held in an inverted

position, and after the nttaimnent of unih)rni iip-niovement.

FIG- 250

FIG. 251

Fk;, ■-")() Kff<H-t of CO., on vri'Dtrojiic ri'spmi.-^i' of Miutc^n npplicil at arrow ;
."-('coiid airow vvitliiii a circle ro|ircs(MiTs siibst itiit ion of frc^li aii-.

Fi<;. 'Jol EfFoct of CO, on <,''eotro]iic ros])on^^c of /■.'ri/fliritm iiiiHra. Succes-
sive dots are at intervals of a minute.

carbonic acid gas was aj)plied ; tiiis cau.scd a reversal of the
normal geotropic movement in the course of four minutes
and twenty seconds; the petiole was thus iowcicd below its
original position. Introdudion of fresh air gave rise, in
the course of two minutes, to the renewal of the normal
erectile movement (Fig. ^o] .)

The results obtained with various growing" and juilvinated
organs thus show that the normal geotropic- response is
reversed liiider the continued action of caihoiuc acid gas.

CARBON DIOXIDP: ON GEOTROPIC ACTION t'A\^>

X/ynn* has also sliown that a reversal of geotropic curvature
ot'curs wlien the hypocotyls of H rliantJiUS annuus are fixed
horizontally in an atmosphere containing from 9 to 30 per
cent, of carbon dioxide. On tlu> removal of the carbonic
acid, the seedlings showed a noniiai upward curvature l)y
next morning. Lynn did not notice any preliminary
■enhancement of geotropic curvature, the method of eye
■observation employed being not adequate for the purpose.
For an explanation of the phenomenon he suggests the theory
•of hydrion concentration ; an assumption is made that the
stem is a relatively alkaline structure, because the carbon
■dioxide of respiration does not accumulate (most of it being
used up by the plant during photosynthesis) ; it is further
supposed that as a result of the relative alkalinity of the
<^ontiuuous phase of the protoplasm in the perceptive cells, a
horizontally placed stem under normal conditions turns
upwards in response to stimulus of gravity. In an atmos-
phere of carbon dioxide, on the other hand, the stem is
Tendered less alkaline with the result of reversal of normal
response.

This explanation is not satisfactory since there is no

! evidence in support of the Hydrion Differentiation Theory
■of Geotropism propounded by Prof. Small; on the
contrary, accumulation of carbonic acid in the plant in the

I absence of photosynthesis has practically little effect towards
reversal of normal geotrojnc response. Most of the records
given in this chapter were obtained with petioles of leaves,
the photosynthetic lamina being cut off; moreover the
■specimens were kept in a dark box. In spite of these con-
ditions the geotropic response produced was a normal u]i-
€urvature. Finally, the immediate effect of carbon dioxide
is an enhancement of normal geotropic action — a result
which contradicts the hydrion theory.

* M. J. Lynn. M.sc. . " The Reversal of Geotropic Responfie
in the stem.'" The New Phytologist— August, 19, 1921. •

^66 hlFV. MOVEMENTS IN PLANTS

EXPLANATION OF TIIK REVERSAL.

In regard to the reversal of the normal response it might
be thouglit that the geotropic perception might in some
way undergo change in an atmosphere of carbon dioxide.
In reference to this, investigations with the Electric Probe,
previously described, have fully confirmed the theory that
in higher plants, it is the falling starch grains that cause
geo-perception ; since the weight of these particles remains
constant, there could be no possibility in the variation of
this factor. It niiglit be argued tliat the starch grains
become absorbed in an atmosphere of carbonic acid gas, the
particular factor of stimulation being thus eliminated. This
argument is, however, untenable, since the reversal under
carbonic acid and restoration of normal response on removal
of the gas take place in the course of a few minutes r
the disappearance and reappearance of the starch grains
could not possibly have taken place within such a short time.

Eeturning to the question of normal geotropic curvature
in growing organs I have shown* that this is brought about
by differential growth, that the upper side of the horizon-
tally laid organ undergoes a retardation of growth, while
an acceleration of growth and expansion takes place on the
lower side. A satisfactory explanation of the effects of
various narcotics — an acceleration, an arrest, or a reversal —
may therefore be found from the determination of the effects
of various narcotics on growth itself. Let us first consider
the enhancement of geotropic up-curvature under moderate
application of ether vapour. This increased up-curvature
may be brought about :

(1) by the increased contraction of the upper side due to
■diminished rate of growth under the anaesthetic, or

(2) by the induced expansion and enhanced growth of
the lower side of the organ.

• Lifo Movpnionts in Plants— Vol. II. p. 50f.

CARBON DIOXIDE ON GEOTROPIC ACTION 667

We are in a position to decide between the two alter-
natives, by finding whether ether induces a retardation or an
enhancement of growtli. If it induces a retardation, tlie
•enhanced geotropic curvature would be due to the contrac-
tion of the upper side ; an acceleration of growth under ether
•would, on the other hand, show that the enhancement of
geotropic curvature was brought about by the increased rate
-of growth at the lower side of the organ. The results of
investigation on the effect of ether already described show
definitely that it induces an enhancement of the rate of
growth. Hence the modification of geotropic curvature
under tlie anaesthetic is due to the induced cliange of growth
of tlie lower side. This deduction also follows from
the general consideration that the upper side of the organ
is contracted under the geotropic stimulus, whereas the
lower side is in a state of active growth. ]^Iodification in
the rate of growth is likely to occur in the growing portion
•of the tissue rather than in the portion where it has become
■arrested under the action of stimulus. A crucial experiment
will be described which will show that carbonic acid gas
•exerts little or no effect on the contracted side of the organ.

Our attempt to discover the cause of reversal of the
geotropic response under carbon dioxide must, therefore, be
-concentrated on the determination of the effect of the gas
on growth. In regard to this, the only information that
has been available is that the presence of oxygen is necessary
for normal growth, and that growth comes to a stop in an
atmosphere of carbonic acid gas. This does not however
-explain the increased geotropic curvature at the beginning,
nor the reversal under its continued action. Certain results
which were obtained with the High Magnification Cresco-
graph showed that the preliminary effect of carbonic acid
is an enhancement, while continuous action causes a
retardation of growth.* This would fully explain the

* Life Movements in Plants.— Vol. II, p. 265.

•^68 LII'l': .M(>\I'.\II',N I > IN PLANTS

iiiitiul increase of the ^eotropic ciirvj't-ure under carlxjnic
acid and the subsequent arrest. I'^urther in\ estimations are
however necessary to determine the etVeci of continued
action of catl)()nic acid in indiicin;^ a re\ct>al, and the after-
effect on the removal of the ^as. I'he follow inm investiga-
tions were th(M'clore carried out on the ctfcct of carhonic acid
on ^cowth as regards: (1> the immediate elVect . ci' the
persistent effect, (^}> the al'tcr-eifect on the removal of the-
^as, and (4> the effect of carhonic acid ^as on an or^^an
conti'acted under continuous stimulation.

INVKSllOATloX ON \1( lOI flCATION OF (IROWTH XJNDER
CMU'.oNlC ACID GAS.

The Hi^ii MaiiJiifK alion ( rescograph was employed for
record of the normal gi'owth and its induced variation. The
tiower-bud of Criiniin lily was found suitanle for tliis research,
as its normal rate of growth is very nniform. The magni-
fication employed was a thonsand times, and the successive
dots in the record indicate intervals of 20 seconds. The
specimen was enclosed in a chandler which could he filled
with pin-e carbon dioxide for a definite length of time, air
being afterwards substituted for the gas.

The rate of normal urowth of the Crininii lily was taken
on a mo\ing plate, and th(> slope of the curve and the
closeness of the successive dots indicated the
tuHuial rate. ( arbomc acid gas was intro-
duced into the chand>er: this is seen to iiave induced an
almost immediate enhancement of the rate of growth as seen
in the erection of the curve and the wider spacings
between the dots (I'^ig. 'i-Vi*. This induced enhance-
ment of growth lasted for \ mimUcs. <iftcr irhic}i
a (■(,}itr<icfl(>ti took J>l(ic( (»i (icrount of irhirh tJic
apcriun't] hccuDn shortir flnni (it tin' txijinmnij .
thin <-ontrn<-tio}i }><T.<il^t('(l fliroiKilioiit tlir a}>}>licntion of

CAKIidN l»l(»XII)|'. ON (,l,(i'['i;(i|'l( \('II()\

f)6f)

the ijas. On snbstitution of trc-'<li' <iir flic t/onnal (jrDirtu
ehngatio)! iras; roiuiiicd. Tliis i'esiiiii|>i ion occiirreil in the
course t)! about 4 minutes.

This ivnuirkal)le result of contraction wliicli persists
during tlie application ot" gas. and the restoration of growili
on removal ot" the gas. ott'er full explanation of the rever-al

FIG. 252

FIG. 253

Fig. 252 Eft'ocr of CO, on jrrowth.

Note preliminary enhancement followed liy ;tctive eoiit raetion. under vvliieli
the orsfan became shorter than at the l)ejrinnina'. Substitution fif fresh air
at arrow (within a circle) caused a renewal of growth.

Fig. 253 Organ contracted under stimulus S; application of C'O.^ ai arrow
produces no effect. Renewal of irrowtli on cessation of stimulus ami removal
of aras.

of geotropic res|)onse and the subsequent restoration of the
normal response on introduction of fresh air. The ]>relinii-
narv enhancement of growth under (<> .. also ex[)lains the
immediate enhancement of the geotropic curvature. The
np-curvatnre has been explained to be due to the differential
growth of the upjier and lower sides of the organ. Consi-
derations have also been adchiced to show that the modifica-
tion of geotropic curvature under anaesthetics is brought
about bv the induced change of growth at the lower side of
the organ, the effect on the contracted upper side being

(ITO LIFE MOVEMENTS IN PLANTS

negligible. Tt ^v()ul(^, liowever, be interesting to obtain a
(lirocl proof of this by observing tbe effect of carbon dioxide
on llic growth of an organ contracted under constant
stimulus.

Effect of CO , on an Organ Contracted under Stimulus. —

The record was taken of the normal rate of growth of

Cri)n(}n hl\ , \vliich was next subjected to

Expi-riiiicnt 2(i7 '. , . , . . ,

constant stnnulation under tetamsmg elec-
tric shocks of moderate intensity. This is seen to induce a
maximum contraction. Carbonic acid was next introduced
into the chambei- : the organ remained contracted in
spite of the introduction of the gas. \ transient disturbance
sometimes occurred on the introchiction of the gas, which
<|nickly disappeared, and the organ remained practically in
the same contracted conihtion ;is before. The stimulus was
next (hseontiiuied. and fresh ail" intrcxhiced into the
ehiiniher : th(> iionn;il growth was now found renewed
<b'ig. •2-")."5i. It is thus seen t':at in a geot ropically curved
organ the uppei' and contracti d lialf remains i)ractically
miaft'ectt'd by the introduction of the carbonic acid gas.
A |)rehminary enhancement of growth of the lower half of
the organ followed by contraction explains the increase of
geotiopic curvature followed by a reversal.

VAIMATION OF GEO-ELECTRTC RESPONSE UNDER CARBONIC .ACID.

The experiments that have been described offer the
fullest explanation of the preliminary increased geotropic
response and its reversal under carbonic acid gas. The
subject is, however, of sufficient importance to justify
investigation by the altogether independent method of
electric response.

It has alreadv been shown that under the action of
stimulus of gravity the upper .side of a horizontally laid organ
undergoes an electric change of galvanometric negativity,
indicative of excitatory contraction; the lower side of the

CARBON DIOXIDE ON GEOTROPIC ACTION 671

•organ undergoes, on the other hand', a change of galvano-
metric positivity which is the electric concomitant of
•enhancement of rate of growtli and expansion. The
resultant geo-electric response is thus due to the joint effects
■of negativity of the upper and positivity of the lower, just
as the erectile response under the stimulus of gravity is due
to joint effects of contraction of the upper and expansion of
the lower side of the organ. The electric and mechanical
responses are but different expressions of the fundamental
reactions which occur at the opposite sides of the organ.
'This being so, we would expect that any agent which
increases the existing geotropic curvature will also increase
the existing geo-electric current. Conversely, other agents
•wiiich cause a reversal of the geotropic curvature will also
cause a reversal of the electric current.

Geo-electric Response. — The peduncle of the Tube-

Tose, which exhibits strong geotropic curvature, was found

suitable for the following investigations on

Kxiieriment 26<S , , . „ . , •

the geo-electnc response. iwo electric
'•contacts were made at opposite sides of the organ
by thrusting in two thin platinum electrodes
in circuit with a sensitive galvanometer (Fig. 254).
After the subsidence of the irritation caused by the slight
wound, photographic records of the deflection are taken when
the organ is held vertical ; in the absence of geotropic
-excitation, the galvanometric deflection is found to be
practical Iv zero. But as soon as the specimen is inclined to
a horizontal position a deflection occurs, the lower contact
•becoming galvanometrically positive, and the upper negative;
this deflection soon attains a maximum value, and remains
constant as long as the specimen is held in the horizontal
position. The deflection disappears on the removal of
geotropic stimulus by restoring the plant to the vertical
position. After making the two diametrically opposite

♦;7

I.ll'f MnVKMKN'TS IN I'l.ANTS

contacts with the iumIuucK'. the speeiiiien was placed in a
horizontal position ; tliis i^iive rise to the fjeo-electric response-
wliich attained in ;i short time the niaxinniin value.
Carhonic acid <ias was next passed iido the j)l;uit-chand3er.
This gave rise to prelinu)inni cufKittcctucut of the electric
response foUoired by reversal. Oh su})stifution of fresJi air,
tJtere was ri'sforafioii of flic HaniKil rrsponsr. The ex|)eri-
ment w;is I'cpeated ;i iiiindxM' of tiiii('> with the same
specimen and it was invai'iahly IoiiikI th;it the lico-clectric
response was reversed and restored hy .•ihernatc npphcation
of the ^as and its removal. Mlie residt of the electi'ic
res[)onse is thus pnrnllel to that of the mechanical responstv

ISOI.A'J'ION Ol'' UlsSt'oNSi-; ()!•' ONK SIDI'. ol' THF. oIlGAN.

In the ahove experiments the electric resj)onse \\as due
to the joint effects on upjier and lower sides of the orpan.

Fk;. 2.')4 Klcctrif i-Dniicct ions for Lfeo-i'iectric ri'spoiisi-. 'riic (irst illust ra-
tion siiows cliM'tric contacts witii upjxT and lower sides of oru'an, riic j-on-
tracted upper, e.Tliit)itiii<r jjalvanonietrie nefrativity, and the expanded lower
a jjalvanonietric positivity. Second illustration shows isolated contaet with
the lower H, the second contact bein<j made with indifferent jjoint O, in the
leaf. In the third illustration, the isolated contact is made with the uppei-
side A. The isoliite<l lower contact B exhibits an electric jxisitivity and tin-
upiMT .\, ati clecrric ncLrativity.

The electric method of en(|uiry, liowever. ofiers the unique
Mdvanta;ie of i.solation of tlie effects of the lower aiul the
ii[)per sides, [''or' this we make oi\e electric contact B, whicdi
is to he the lower side; the second contact <> is made with
an indifferent point, i.e. the landna of a lateral leaf. The
res|)onsive variation would in this ease he Awt' to the chaiiL^e
induced on the lower side of the orj^an. h'or ohser'vat ion ol
the induced chanf(e on the upper side, the electric contacts
are made with A, and the indifferent poitit, O (Fij^iire •2-")4).

CARBON DIOXIDK ON OKOTHOI'lC ACTION 673

Effect of COoOn the Lower Side.— Tlie two contacts thus

made svitli O and Ji, gave no detleetion when the organ was

held vertical. The specimen was next

Kxpei-iiiuMit 2HH • i-

nu'lined so as to make it hori/oii^il ; a large
galvanometric detleetion was now induced by the geotro|)ic
stimulus, the lower side B becoming galvaiiometrically
positive (up-curveK indicating" an expansion, enhancement
of turgor, and inc-reased rate of growth. On introchiction of
carbonic acid into the plant-chandler, titcrc occiirnd a sltort-
Jivcd increase of response: after tills the positirr dcflcctidn
iras suddenlij reversed into neiiatire, indicatiiuj thai tJie

FIG. 255 Fl .. 256

Fig. 2'i') Effect of CO., on sreo-ek'ctric respon.se of lower side. Incli-
nation to horizontal jiosition induced sralvanometrie positivity of lowe
side (iip-curve). Application of C0„ at arrow induced a reversal.
Removal of s^as at arrow (within circle) renewed the normal resjionse.

Fig. 2r)H Effect of CO.^ on upper side. Normal electric resjionse is
negative (down-curve). Ap]>licati(>n of CO., or its removal iniluccd little
change.

loirer side had n)ider(jo)te a emitraetion. On the introduc-
tion of fresh air, the normal expansion of the lower side was-
once more restored, as indicated by the restoration of
positive electric response (Fig. •25-")).

Effect of CO,, on the Upper Side. — The isolated electric

contact was next made with tlie upper side A. On placing

the specimen in a horizontal position the-

Experiment 270 . pi ■ ^

geotropu- respon.se ot the upper side was

('(74 LIFK MOVK.MKNTS IN PLANTS

negative (dow ii-ciirxct. 1 iiti-odiictioii or removal of carbonic
;ici(l uas |)f()(liict'(l littl(> oc no cliange (Fig. '256).

The results described above prove once more that the
efl'(M't induced on the upper side is neghgible compared witli
that inchiccd (Mi the lower side of the organ. The strict
concomitance of the nicchariical and electric responses, and
their induced variations will be seen in the following tabular
staT(Mnont of the resuhs.

TAHl.i: 1,.\I. — EFFECT OF CO o ON GEOTROPIC ACTION OF THE MORE
EFFECTIVE LOWER SIDE OF THE ORGAN.

Effect of
Carbonic acid :

Median ical
response.

Electric response.

Resultant geo-
tropic response.

( )i] iiil rodnctioii.

Increased expan-

Increased galvano-

Enhanced geo-

sion.

inetric positivity.

trojiic response.

Persistent effecl .

(Joiit Taction.

(lal van o metric-

11 e V e r s a 1 of

negativity.

resi)()nse.

Kftuct of i-eiiiDval

Normal expan-

Nonnal positive

N o r rn a 1 g c o-

of j^as.

sion.

response.

trojiic response.

SUMMARY

The immediate effect of carbonic acid gas on geotropic
response of growing and pnhinatcd organs is an enliance-
ment above the normal.

Continued action of carbonic acid gi\es rise to a reversal
of the normal geotropic rcs])onse.

This reversal })ersists during continued action of the
carbonic acid. The nr)nnal response is restored after
removal of the gas.

Investigation with the mechaiucal method of response
shows that it is the lower side of the organ whicli is relatively
more alfected by the anaesthetic than tlu^ ujiper side. The

I

CARBON DIOXIDE ON GEOTROPIC ACTION 675-

lower side thus exhibits an initial expansion and increased
rate of growth under carbonic acid fjas, with the resuhing
enhancement of geotropic response. Continuous apphca-
tion of the gas induces a contraction of the lower side causing
a down movement or reversal of the normal response.
Growth of the lower side is renewed on the removal of the
gas with consequent restoration of the normal response.

Electric response under the stimulus of gravity exhibits
effects parallel to those of mechanical response. The effect
of carbonic acid gas is a jireliminary enhancement of geo-
electric response followed by reversal. The reversal
persists during the continued application of the gas; the
normal geo-electric response becomes renewed on the
removal of the gas.

Investigation on the isolated response of the
lower side of the organ offers an independent corroboration of
the above. Introduction of the carbonic acid induces a
preliminary enhancement of galvanometric positivity of the
lower side ; this is subsequently reversed to galvanometric
negativity. Removal of the gas is followed by the restora-
tion of the normal positive response. The electric response
of the upper side exhibits little or no change by the introduc-
tion or removal of the gas.

The reversal of the geotropic response under carbon ■
dioxide is thus due to the contractile action of the gas, .
which is more effective on the lower side of the organ.

LVin.— ox I'HiSlOLOCiUAL AMSOTKOrY

INDUCED BY GRAVITATIONAL STIMULUS.

By Sir ,I. ('. Bose,

Assisted hv

St'rfa'dra Chandra Das. m.\.

Plants have been iisikiIIv da^sitied as ' sensitive ' and
ordinary; the loi'mer is exampliHcd hy Minidsn pudica
Avhich responds to stimnliis l)y a conspicuous movement of
the fall of the leaf. Oidinary plants, on the other hand,
appear to be insensitive under shocks of every kind. I have,
ho^vever, shown that every plant, and c\iMy or^an of every
])lant. responds to stiundus, the niduced excitation being
detected by the electric response of galvanometric
negativity.*

It is, moreover, not true that tlie organs of ordinary
plants do not t^xhibit any niccbaMJcal r(>sponse under
stimulus. In Mi}}tosa the lower half of the pulvinus is
relatively the more excitable; hence under stinndus, the
greater contraction of the lower lialf pulls tlie leaf down;
the actnal contraction in the lower lialf is. however, not
verv great, but the slight uioxcuient is magnified by the
petiolar index. Had tlic upp(M- half of the pulvinus been as
■excitable as the lower half, it is ob\ ious tliat the two anta-
gonistic contractions would have niMni'alised each other.
In such a case excitatory conti'aclions woidd havi^ occinTed,
without any external manifestation of responsive movement.

* Response in the Living and Non Living.
076

I

PHYS10LOO]('AIi ANISOTROPY (W?

In radial organs of ordinary plants the excitability is the
•same all round ; hence the orj^an is unable to exliibit any
lateral movement on account of tlie antagonistic conti'actions
•of opposite sides.

For exhibition of any conspicuous lateral move-
ment the organ should be anisotropic, its opposite sides
being unequally excitable. This anisotropy is normally
found in dorsi-ventral organs like the pulvinus of Mimosa.
It may, however, be induced by the one-sided action of
stimulus, on account of which the stimulated side of certain
organs becomes permanently contracted. An example of
this is found in various tendrils, where the stimulus of
contact causes them to coil round the support. It is evident
that the tissue already contracted under stimulus, can under-
go little or no further contraction ; whereas, the expanded
and unstinmlated length would exhibit a responsive con-
traction. It thus follows that the contracted and concave
side of the tendril would prove to be less excitable and
contractile, than the expanded convex side. A physiological
anisotropy may thus be induced by the unequal action of
the stimulus on two opposite sides of an organ, and in the
case of the coiled tendril, the anisotropy is permanent
The fact of the coiled tendril being physiologically aniso-
tropic may be tested by subjecting it to the diffuse stimulus
of tetanising electric shocks. The response of the tendril
is then found to be a movement of uncoiling due to the
greater contraction of the hitherto unstimulated convex side.

These considerations lead us to expect that under
-suitable conditions, a temporary anisotropy could be con-
ferred on radial organs by the unilateral action of stimulus
When a radial stem is laid in a horizontal position, a geo-
tropic curvature is induced, a particular side A, which
happens to be above, becomes contracted while the opposite
side B becomes expanded. One would, therefore, expect

CIS TJFR MOVKMKNTS TN PLANTS

that under tliese coiulitions an induction of anisotropy l)y
which the upper side A is rendered less excitable than the-
opposite side B. The anisotrojjv would, however, be not
permanent ; for by turning' round the stem through 180°, the-
above relations woidd be reversed. 15 would now become con-
tracted and A exjnindcd ; A Avould now be rendered more
ex('itai)ie than J3. From theoretical considerations detailed
above, we see the possibility of an ordinary radial organ
being rendered ' sensitive ' after being subjected to tlie
stimulus of gravity. For a geotropically curved organ is no
longer radial but anisotropic, and the more excitable convex
side would thus function like the more excitable lower half
of the pulvinus of Mimosa. The response to diffuse
stimulation would be similar in the two cases, namely, a
down-response due to the greater contraction of the lower side.
The only difference between the two would lie in the fact
that in the geotropically curved stem, the induced differen-
tiation is temporary, whereas, in the dorsi-ventral pulvinus
it is permanent. We shall next inquire whether the above-
inference is found verified by experimental results.

METHOD OF INVESTIGATION.

We take various radial organs of plants, and subject
them to electric shocks. No lateral response is produced,
since their different sides are equally excitable ; the anta-
gonistic reactions thus neutralise each other.

This absence of effect under diffuse stimulation is obtain-
ed immediately after laying the radial organ in a horizontal
position. For, a certain length of time is required for in-
duction of physiological anisotropy under the action of the-
stimulus of gravity. After the attainment of geotropic up-
curvature the lower or convex side is rendered the more
excitable, and diffuse stimulation by electric shock induces-
a down-movemenl by the greater contraction of the

PHYSIOLOGICAL ANISOTROPY 679

lower side. If next a geotropic.illy curved specimen be held
inverted with the convex side above, diffuse shock would
cause a contraction of the upper convex side with a resulting
ui)-)it('V()}}C}it. The intermediate case is the one in which
sufficient time had not been allowed for physiological
differentiation when there is no response. Diagrammatic
representation of the three cases are given in Fig. 257 ; the
following experiments are in verification of the above. The

Fig. 257 Diagrammatic representation of responsive movements under
diffuse stimulus in geotropicallj curved organs :

a) Organ curved upwards. Responsive movement downwards seen

in dotted outline,
{h • No response in specimen before induction of anisotropy,
c) Geotropically curved specimen held inverted. Response by up-
movement.

results described below^ may be obtained with different
curved organs. As a typical case we may take the seedling
of Eclipta erecta which is very sensitive to geotropic action.

RESPONSE OF GEOTROPICALLY CURVED ORGAN.

Response before induction of physiological anisotropy . —
The responsive movement of the specimen is obtained by
means of an Oscillating Eecorder, the
successive dots being produced at intervals
of 40 seconds, the recording lever producing a magnification
of 20 times. The radial stem of Eclipta is laid horizontal,,
and tetanising electric shocks passed through it before the
induction of geotropic curvature. The applied stimulus
induced no responsive movement, either up or down (Fig.
2.58&).

680 LIFK MOVEMKNTS IN IM-ANTS

Response of up-curved organ. — The stem was next

allowed to curve upwards under geotropic action, and record

of response obtained under electric stinnilus.

Kxporiinoiit 272 .

It was tlius tound that responsive down-
movement occurred under a niiniinal stinndus which w^as
just effective in iiuhiciug the responsive movement of
Mimosa. Thus as regards minimally effective stimulus the
sensitiveness of ordinary j)lants is found to be of the same
order as that of the much lauded Mimosa. As regards the
apex time and the ptMJod of rin-overy the responsive
characteristics of the ordinarx stcni arc int(M-iiie(liate botW('<Mi

I'm.. 2")S Ki'^ponst" 'jf ji'iM)tr()|iic"illy cursed orti'.-in iimlcr cxti'i'iiM 1 stimulus ■
((/) KcsjMdiso of ui)-curvc(l or<^iiii by (lowti-iuoNcincnl . 'I'liciuo rri;()rils

arc Tor feeble and moderate stiiiiuhis,
(/<) Xo response before induction of aiiisot mps ,
(/■) Iles])onsc 1)\ an up- iiiovctricn: in an up-cni'\ed or^'an. licld inNcrled.

those of sensitive plants. Miniasd piidicti and Xcptinna
oleraccd. in the former tiic apex time. i.e.. the period
for the attainment of niaxiniuni contraction, is three seconds,
the period of recovery being IT) minutes. In Xcjihniln the
niaxinunn contraction is attained in the coiu'se ol ISO
seconds, and tlie rt^covery is only complete after ()i) minutes.
In regard to the above, it is to l)e remembered that the
recovery is relatively quick after feeble, and very much pro-
tracted after strong stimiilalion.

In the ri'sponse of geol Topically curved organ the a[)ex
time is al)ont I'JO seconds, which is slower than in ^fim(>sa

PHYSIOLOGICAL ANISOTROPY 681

but quicker than in Neptunia. The period of recovery afr.er
feeble stimulation is ;"> minutes and after strong stimuhis 15
minutes (Fig. 258a). The period of recovery is about
same as in Mimosa but quicker than in Neptunia.

Response of an inverted organ. — The geotropically

curved organ is next placed in an inverted position, the

convex side being up. Response to electric

Experuiient 273 ... .

stnnulation is now upirards due to the
greater contraction of the expanded upper side. Two
successive responses were obtained with (1) feeble and (2)
strong electric stimulus (Fig. 258c).

HKVERSAL OF AN1S(JTI^)PY WITH CORRESPONDING REVERSAL OF

RESPONSE.

After obtaining the response in the inverted position the

specimen was allowed to remain in that position. The

geotropic stimulus now tended to reverse the

Experiment 274 i n ■ i •

curvature of tlie organ })laceti m trie inverted
position. The convexity of the upper side gradually dis-
appeared and with it, the induced anisotropy; the stem
became straight and radial; electrical stimulus now induced
no responsive movement. After a further interval of time
the original curvature became reversed, the lower concave
side now became convex and relatively the more excitable.
Electric stimulation was now found to induce a responsive
movement downwards. Thus experimenting with an
identical specimen, held with the convex side up, the
response was at first upwards; under geotropic action the
organ became straight, when there was no responsive move-
ment. The organ then became concave, and gave the
downward response. The changing internal differentiation
in an identical specimen is thus detected by a definite trans-
formation from an up-response to zero, and finally to a
down-response.

("82 Lll'R MOVEMENTS IN PLANTS

The response oT a geotropically cnrvetl organ has thus
been shown to be similar to tliat of the piilvinus of the-
Mi)inisa; in botJi we obtain a responsive down-movement
under external stimulus such as that of tetanising electric
shocks. We shall presently find that this resemblance
extends even in ail essential details. Thus the response of
Mi)ii(>sa is moditied in a definite way by the condition of sub-
tonicity. It is also affected by the action of anaesthetics,
the efl'ect being modified by the dose and duration of
application.

ABNORMAL POSITIVE RESPONSE UNDER CONDITION OF SUB-
TONICITY.

Positive respojise in Miino.sd. — .\n experiment has-
already l)een described (Kxpt. 50, ^'ol.

Expcriinoiit 27-'' -, "„ 111 i

i, p. 14/) which showed that when the
Mimosa plant is kept in unfavourable condition such as
darkness, its tonic condition falls below par. In this sub-
tonic condition the response to stinudus is not by the normal
fall of the leaf (negative response) but by the abnormal
positive or erectile movement. Under the action of
successive stimulations, the tonic condition of the tissue is
improved and the response becomes gradually converted from
the abnormal positive to the normal negative.

The experiment is varied in the following way ; a cut
specimen of Mimosa is taken in a vigorous condition ; the
response of the leaf to moderate electric stimulus is found
to be normal negative. Tlie sj)ecimen is next kept in a darlc
cupl)o;ii(l for about 1 '2 hoiu's, wlicn the response is found
to be converted into the abnormal ]iositive. After exposure
to day light outside, response of tlie specimen is found to be
restored to the normal negative.

PHYSIOl.OC.lCAT. ANISOTHOPY 6H.S

Abnormal positive response of geotropically curved
stem. — We shall next observe the most striking parallelism
in tlie response of Mimosa and of geotropic-
ally turved organ under condition ot siib-
tonicity. We found that the normal response of a geotro-
pically curved organ is always by a down-movement in a
specimen held with the concave side upwards. Half a dozen
curved specimens were next placed in a dark room for 5 or
6 liours, and all of them exhibited a reversal of resjionse,
which was now by an tip-movement. The specimens were
next exposed to diffuse light of the sky or of sunlight for
111 hour. After this the response of all the specimens was
haind to be normal, i.e., bv a down-movement.

.AlODIFYIXO ACTION OF ANAESTHETICS ON RESPONSE TO
EXTERNAL ST^rULUS.

Account of detailed investigation on the effect of
anaesthetics has already been given in the previous chapters.
It was shown that the effect of an anaesthetic like ether is
to cause an enhancement of response ; continued applica-
tion however causes a depression or abolition of irritability.
Effect of ether on geotropically curved organ. — The
normal response of the geotropically curved organ is first
ol)tained, after which dilute vapour of ether
..\peiiiiien t, .^ introduced into the plant-chamber.

Successive responses to equal stimulus are next obtained
after etherisation lasting for 1 minute, for 15 minutes, and
for 30 minutes. From the record of responses thus obtained
Ave find that the amplitude of the normal response is -4 mm. ;
after one minute's application of ether the amplitude is
-■nhanced to 14 mm., or more than three times the normal :
?fter 15 minutes there is a further enhancement, the
amplitude being 24 mm. or six times the normal. But

€84 LIKK MOVKMKNTS IN ]>LANTS

after thirty minutes all responsive nioviMuent is f()iin({
paralysed (Fi^. -J-V.)).

Effect of Carbonic acid and ol Chloroform. — The effects:

of tliese inild and titron;^ anaesthetics arc found essentially

similar to that of ether, the only difi'erence

Exporinioiil 27>> , . , . .,.' ,. ,

heni^ n\ the relative rapidity oi the
characteristic chanj^es, which is very (|ui<k' under
chloroform and slow undt>r carhonic acid.

Tfir innnrdidic effect of (ill hinds ai umiistlieties is (in
euJidiieenieiit of response of the (jrol rojn'enll ij eiirred orijun

Vn.. •_'.">:( litl'cct ol tiliir vaj)i)ur on n'>-])i)nsc of trcot ropically ciirvt'd or>jfaii.
Tiie fii'st is tlic iiorriiiti, ttic second, lliini niid the foiii-tli lire iH^siioiist's under
fontiriiied aelioii ol" etlicr.

Note tlie iiicruiiMe of resjirms)^ tollowtMl hy ;iii ;irresl.

to c.iicrnal fttiniiilus ; eoHfinned netion of (nidestlicties causes
an abolition of response.

Hie effect of (nidestliefies on response to c.rfcrndl
stitnuhis is precisely flic s<nne as that to internal stiniuhis of
(jravitij. l-'or the rate of (je(dropie niovenient is enJinnced
under the ininicdiatc action of (inaestheties and arrested
after continued application.

A wide generalisation is thus reached as regards the
effects of anaesthetics in regard to response under externa)
and internal stinndation.

PHYSior.onic'Ar. anisotropy 685

SUMMARY.

A radial organ is equally contractile on its different sides ;
hence diffuse stimulation induces no resultant lateral
movement, which is prevented by equal and antagonist] -
contractions at diametrically opposite sides of the organ.

In dorsi-ventral organs like the pulvinus of Mimosa,.
there is a physiological anisotropy which is permanent. The
pulvinus under diffuse stimulus responds by a fall, due to
the induced greater contraction of the low^er side.

In ordinary plants a physiological anisotropy is induced
by unilateral action of stimulus. In a tendril coiled round a
support, the contracted and concave side is rendered less
excitable than the expanded convex side. Diffuse stimulus
induces greater contraction of the convex side with the
resulting movement of uncoiling.

In the two cases described above, the anisotropy induced
is permanent. But the anisotropy induced by the stimulus
of gravity is temporary. In a geotropically curved organ,
the contracted and concave side i? less excitable than its
diametrically opposite convex side. Diffuse stinmlus is
found to give rise to a responsive down-movement, i.e., in
a direction opposite to the existing curvature.

The sensitiveness of ordinary {)lants thus rendered
anisotropic under geotropic action, is of the same order as
that of the ' sensitive ' Miynosa. The apex time is 2
minutes and the period of recovery 15 minutes.

The anisotropy of the geotropically curved organ, held
in an inverted position, undergoes continuous change
culminating in a reversal. The internal transformation is
detected by the responsive reaction evoked under external
stimulus. Thus response of a curved organ (held in an in-
verted position) is found to change from an up-move-
ment through zero to a down-movement. The first is the
case when the upper side of the organ is convex, the second.

tj86 LIFE MOVKMKNTS IN I'LANTS

Avheii the organ is straight, and the tliird when the upper
side is concave.

The sign of response of geotropically curved organ. Hke
that of the pulviinis of Mi))}osa, l)ecoines reversed under
condition of sub-tonicity. Application of stiinuhis. raises
the tonic condition to the normal with corresponding
restoration of the normal sign of I'espcnse.

Anaesthetics induce a ])reliminary onliancement of
responsive movement followed, under continued action, by
an abolition.

The effects of anaesthetics on response to external
stinndus are in every way similai" to those of internal
stimulation under gravity. The response of a curved organ
and the rate of geotropic curvature is enhanced under the
immediate action of anaesthetics and abolished under
continued action.

A generalisHtion is thus reached of the identical effects
of anaesthetics, in regard to both external and internal
etimtdation.

LIX.— THE DEATH-SPASM IN GEOTEOPICALLY
CUEYED OEGANS.

By Sie J. C. BosE,

Assisted by
Ai'URBA Chandra Nag, m.sc.

We have seen in a previous chapter that a spasmodic
■death-contraction occurs under toxic doses of chloroform.
In radial organs this spasm is exhibited by the shortening of
the length (Experiment -249). In piilvinated organs it is
•shown by the greater contraction of the more excitable half
of the pulvinus (Experiment 257 ). This irreversible change,
associated with death, is shown by the fact that substitution
of fresh air for chloroform vapour does not revive the plant ;
a death discoloration soon spreads over, and the plant
becomes flaccid from loss of turgor. Since the particular
spasm indicates the onset of death in ])lants, it might be
possible to detect the critical point of death brought about
by other means. Thus a plant subjected to the gratlual
rise of temperature would succumb as soon as the fatal tem-
perature is reached. I have shown elsewhere* that this
death-temperature may be accurately determined l)y
taking a contintious record of the responsive movement of
the plant caused by the rise of temperature. Thus on
subjecting the sensitive plant Mi)}iosa pudica to a gradul
rise of temperature at the standard rate of one degree per

*Bose — Plant Response, p. 168.

,, Comparative Electro-Physiology, p. 546
687

688 l-IFK MOVKMKNTS IN PLANTS

minute in a thermal l)ath, tlie leaf was found to be
continuously erected till tlic tt^iip'^ratun^ reached the
critical degree : the erectile movement was thenf
suddenly reversed into a sj)asmodic down-movement^
this latter, being in fact the excitatory fall of the leaf.
The critical temperature was found to be at or ikmu' CA)°('.
After this the plant was found to be permanently irrespon-
sive. Repetition of the exjieriuKMit sjiowcd Tieitlun' the-

Km,. 'Jtill l)(';it li.sj)aMii ;it t lie cril ic;i 1 l(iii|i«'r:il lire :

{(i) l-'ii-.-i |i:irl (if the inirvc sluuvs cdiit iiiuoiis erect ion of the
leaf of MiiiKisd (liiriiiir liM' of tcniperature froiri 2">" to
tiO". The deal h-spasiM of suildcn fall of the leaf occurred
at KO"C.

(M Dcalti-spastM of i-cc(llili-- of llrli,n,lln,s ,1,11111',:^ -Ai (U"C.

preliminary expansion nor the final spasmodic contraction-
In plants with thick stems, tiie attaiiunent i>i the interior
of the plant of outside fatal temperat\u'<', nnist be a slow-
process; hence such |)lants have to Uo subjected for a long
time to the critical temperature to ensure death. But
fleedlings quickly succumb to the action of death-tempera-
ture. Thus similar seedlings of Mimosd were divided in-
to two batches and placed in the same bath, the rate of rise-
of temperature being 1°C. j)er minute. The first batch*

DEATH-SPASM IN GEOTROPICAfLY CURVED ORGANS QS'}'

were taken off from the bath at the temperature of 58°C.,-
which was two degrees sliort of the fatal temperature, and
replaced in water. The second hatch, placed in the thermal
bath, exhibited the spasmodic fall of the leaves at 60°C. ;
these were also taken out and placed in water at ordinary
temperature. The tirst batch exhibited after two hours,,
renewed signs of life and excitability, whereas, the second
half never revived. Hence the spasmodic movement of the
fall of the leaf may be regarded as the death-spasm, corres-
ponding to the death-throe in animals. The occurrence of
death-spasm I have shown to be very general, not merely in
sensitive, but also in ordinary plants, and in all their
organs. Thus ordinarv growing shoots and also-

«

^Bm

^

^^^B

'•'•..... . . .

•■:',','.

"j

/ V \

,•

.•Vy-.C

^HM^^l

3g"C- .

~K

62°C.

Fig. 2^1 Death-hipasni in rhf luilMUin;;-
leaflet of Desmodium gyraiis

Note spasmodic contraction at 82"C.

the roots are found to exhibit a similar spasmodic death-
contraction at temperatures betw^een 60° and 62°C.
(Fig. 260). This death-spasm also takes place in the actively
rhythmic leaflets of Desmodium gijrans. In Fig. 261 is

tJ90 Lll'K .MOVK.MKNTS ]N PLANTS

seen a eoiitimious record of pulsations of this leaflet as the
temperature of tlie i)lant-chamber was continuously
increased from 30° to 63°C. The frequency of pulsation
was found at first to be enhanced; this was followed l>v ;m
arrest and subsequently a contractile spasm occurred at
62°C'. The characteristic spasmodic death-contraction is
thus exhibited by all vegetable tissues, ordinary, sensitive,
and rhythmic.

The fact that a temperature of about 60°C. is generally
fatal to plants, is supported by independent results of electric
investigations. The electric response of galvanometric
negativity which characterises the living condition of the
plant, is found abolished when the specimen is raised above
fiO^C. This may therefore be regarded as the fatal
temperature for most ])lants.

<»iie ))lausible explanation of the sudden contraction at
the critical temperature is, that it is not an excitatory
reaction, but due to the coagulation of the protoplasm. The
following evidence, however, strongly su})ports the view
that the plienomenon is one of excitation.

1. Were the phenomenon one of mere coagulation,
we should expect a steady and continuous contraction with
the rise of temjierature, the contraction remaining persis-
tent with the coni]iletion of coagulatioii. But instead of
this, we find at first a growing ex])ansion at a moderate rate,
on account of which the leaf of Miuiosa becomes erected.
On the attaimnent of the critical temperature, however,
there is a)) al)ru))t inversion of the erectile movement shown
by the sudden fall of the leaf. ^Moreover, after this
spasmodic contraction, there is often a gradual disappearance
of the rigor, parallel to the post-mortem relaxation of the
animal tissue. These three phasic reactions, the prelimi-
nary ex])ansion, the death-contraction, and the post-mortem
relaxation, are exhibited by a specimen which had iieen

DEATH-SPASM IN GKoTKoPlt'AI.I.Y CURVKD ORGANS 691

alive. But once it had passed througli tlie temperature at
which the spasm takes place, there is an abolition of all
response ; repetition of the experiment shows neither the
preliminary expansion, nor the spasm which had been
previously exhibited at the fatal temperature.

2. In the case of coagulation, the shrinkage would be
non-discriminative and general, in contrast to the excitatory
responsive movement, the direction of which is determined
l»y the differential excitability of the two halves of the motile
organ. The spasmodic movement exhibited by different
plants at the critical temperature is directive, there being
induced a greater contraction of the more excitable half.
In Mimosa, it is the lower half which is the more excitable,
hence the spasmodic fall is downwards. In a spirally cut
peduncle of Allium, the inner half of the spiral is the more
excitable, hence the response at the critical temperature is
a sudden curling movement. But the spiral tendril of
Passiflora, in which the outer half is the more excitable,
exhibits the death-spasm by an uncurling movement.

8. If the phenomenon were one of physiological
excitation, it would be appropriately modified by physiolo-
gical change in the tissue : this is actually found to be the-
case. Thus fatigue lowers the temperature at which death-
spasm takes place, proportionately to the extent of fatigue ;
in a particular experiment the death-point was thus lowered
from the normal 60°C. to 37°C. Poisonous solutions are
also found to lower the death-point.

4. The question whether the spasmodic movement is
due to coagulation or to excitation may be decided by a
definite test. Excitation may not only be detected by a
visible movement, but also by an electrical manifestation,
totally independent of the mechanical movement ; a tissue
thus becomes galvanometrically negative under excitation.
Employing this test I found that, at the fatal temperature, an
abrupt negative electric variation takes place in the tissue.-

*(i92 LIFE MOVEMENTS IN PLANTS

5. Excitation also gives rise to a concomitant diininu-
tion of the resistance of the tissue. A sudden diminution

-of resistance is found to take place at the critical death-
temperature. The two records given in Figure 262 exhibit

4he sudden inversion of the (•urvo^; at the critical temperature

Pig. 262 Dct(>riiiin;it inn (if t lie ili';il li-poiiit liy

(n) electroiiiolivo, mid

(?i) resistivity viU'i;itic)ii. In i he tnriiicT llu' clpctro-
motivc variiit idii at tlic <'ritical point is a
cliaii',''!" finm clcctni-positivity to t'li'ctro-nega-
tivity ; in I lie latter, from an iiii-reasing to a
suddenly decreasing electric resistance. The
deatl)-i)oint is about ti ,"C.

'by the ('leciroiiioti\(' change of galvanometric negativity
:and by the sudden diminution of the electric resistance.

The con.siderations adduced above would appear to l)e
Klecisive in support of the conclusion that there is an
-excitatory reaction in the tissue at tiic mnincnt of death.
A conclusive proc^f of this will be found in a later chapter,
•where an independent method will be found described in

DEATH-SPASM IN GEOTROPICALLY CURVED ORGANS

G93

<iemonstration of the excitatory impulse generated at the
moment of death.

DEATH-SPASM IN GEOTROPICALLY CURVED ORGANS.

We have seen that in a permanently anisotropic organ
dike the pulvinus of Mimosa, a death-spasm occurs at or
-about 60°C., the excitatory reaction causing a violent con-
tractile movement ; tliis gives rise to the fall of the leaf.
We shall next observe whether a radial organ, rendered
anisotropic by the action of gravity, also exhibits a
spasmodic movement at a critical point, and if so, determine,
the death-temperature.

Death point of a geotropically curved organ. — For this,

a specimen of Basclla aUxi was taken which had undergone

a geotropic curvature. The specimen was
Experiment 279 i , ■ ^111

placed \n a water l)atn wliose temperature

was gradually raised from 40°C. upwards. By a simple

Fig. 2H.H l)eath-.^l)asm in the treotropically curved
Basella alhii. A sudden down-movement occurred
at 61"'C.

device the plate was made to oscillate for each degree rise

t;y4 LIFE MOVEMENTS IN PLANTS

of leinpeiature, hence successive dots represent rise of tern-
jxTatiac of 1°C'. As the temperature rose gradually there
was a slight movement of erection; but as soon as the
temperature reached 61°C., there was produced a sudden
and violent down-movement which represented a contrac-
tion of the more excitable lower and convex side of the organ.
This intense reaction is independently exhibited by the very
erect curve of down-movement (Fig. 263).

SUMM.^RY.

Different plants under a toxic dose of chloroform
exhibit a death-contraction. In the case of radial organs
this is shown by sudden shortening of the length ; in
pulvinated organs, the death-contraction causes a sudden fall
of the leaf.

The critical temperature for death of the plant may be
determined from continuous record of movement of the
plant under rising temperature. It is thus found, that a
spasmodic contraction takes place at the critical point
which is at or near 60°C. The plant is killed after being
subjected to a temperature above this critical point.

In radial organs this death-contraction is exhibited by
a sudden shortening of the length. In Mimosa the death
sj)asm is exhibited by a sudden fall of the leaf due to greater
contraction of the more excitable lower half of the organ.

The death-point may also be determined by the sudden
electromotive variation of galvanometric negativity and by
an abrupt diminution of electrical resistance which takes
place at or about fiO^C.

In a geotropically curved organ the death spasm also
takes place near 60°C. This is exhibited, as in the case
of the pulvinus of Mimosa, by a sudden down-movement
caused by the contraction of the more excitable lower side
of the organ.

LX.— THE COMPLEX EESPONSE OF PULVINUS
OF MIMOSA TO TEAXSMITTED EXCITATIOX.

By Sir J. C. Bose,

Assisted by
Satyendra Chandra Guha, M.Sc.

The piilvinns of Mimosa translates the invisible excita-
tion transmitted from a distance into movement. It may,
therefore, be termed as the Effector. We are accustomed
to regard this organ to consist only of two functional halves,
the upper and the lower, the responsive action being
supposed to be a simple rectilinear down- and up-movement.
In reality, the responding organ is highly complex; for it is
found to give certain other responses which had hitherto not
been suspected. Thus, in addition to the down- and up-
movements, it exhibits right-handed and left-handed twists,
that is to say, torsional responses clockwise or anti-clock-
wise. The motor organ thus consists of four effectors by
which the four distinct types of responses are brought about.

Record of torsional response. — The torsional response is
obtained as follows : in order to eliminate the effect of the
weight of the leaf, and also for obtaining pure torsion, the
petiole is enclosed in a hooked glass support with a smooth
internal surface. Friction and the effect of weight are
thus practically eliminated ; the circular support prevents any
up- or down-movement, yet allows freedom for torsional
response. The torsion is magnified by an L-shaped piece
of aluminium wire appropriately tied to the petiole, so that

G

iVX>

TJFE MOVKMKNTS IN PLANTS

the long anil is at right angles to the petiole. The end of
the arm is attached by a silk thread to the short arm of a
recording lever; there is thus a compound magnification of
the torsional movement, a left-handed torsion producing an
np-ciirve, and a I'ight-handed torsion a, down-curve. The
record is obtained by the Oscillating Recorder, the successive

Fij^. 2H4 Mothoil of ohlaininj^f torsional ros))<)iiso. Stiiiinlation of tlic
tirst siib-))L'tiole to the left induces left-liandcd, and of the fourth sub-
petiole, a ri|;ht-haiide(l torsion. Stimulation of the second sub-petiole
induce a raiiid down-movement, that of tlie third sub-petiole, a slow uj)-move-
iiM lit. For record of rectilinear niovement, the hooked support is removed.

■dots being at definite intervals of time, which may be varied,
according to requirements, from 20 to 60 seconds. The
same apparatus may he used lor obtaining the up and down
records. For this, the hooked support is removed and the
short arm of the lever diroftly attached by a thread to the
petiole ^Fig. 264).

COMl'I.K.X IJKSJ'ONSK OK PII.VIMS 6!>7

"VVe shall now si inly liie effect ol" tniiisniitted excitation
■caused bv successive stinuilation of the 4 sub-petioles. The
characteristic responses are found to be the same whatever
be the mode of stimulation, uiecliaJiical, electric, or photic.
<'are. howevei-, lias to he taken so tliat the stimulus is not
"too strong, for excessive stiundation becomes diffused and
"thus causes a fall of the leaf bv the predominant contraction
of the lower half of the ]iulvinus. Electric stimulation by
letanising electric shocks has the advantage that the inten-
sity may be reduced to any extent desirable; again, strong
light from an arc lamp may be thrown down on a particular
•sub-petiole, and the intensity of stimulation suitably
increased by prolonging the duration of application. The
stimulation {produced by light, generally spepking, is less
intense than that caused by electric shocks, and the reaction
under light is, therefore, relatively sluggish. The different
-sub-petioles will be distinguished by definite numbers,
■counting from the left, the observer being supposed to face
the central stem. The sub-petioles 1 and 4 are the tw^o
<e:xtremes, the two intermediate ones being 2 and 3.

Response to electric stimulation of sub-petioles 1 and

4. — The sub-petiole number 1 is first stimulated by

moderately feeble electric stimulus of short

Experiment "iSO t • * i

duration ; the response is seen to be a left-
handed torsion, represented by an tip-curve : The response
is initiated in a short time, and there is a recovery on the
cessation of the stimulus. The sub-petiole numbfer 4 is next
subjected to stimulation and we obtain a similar torsional
response, but now in a right-handed direction, seen as a
do^vn-curve. The first pair of records are seen one below-
the other (Fig. ^GoE).

Response to pliotic stimulation of 1 a}id 4. — In order to

demonstrate that different modes of stimulation induce an

identical effect, the sub-petiole 1 is now

.xpenmen _, stimulated for a certain length of time, by

throwing down on i^ a strong beam of light from an electric

698 LI IF- movp;ments in plants

lantern. The response is, as in the last case, a left-handed
torsion. Stiniiilatioii of mnnber 4 induces, oi tiie other
hand, a ri^ht-handed torsion. (Fig. 2f);)L).

Stimulation of sub-petioles 2 and 3. — We next observe

the responsive movements caused by stimulation of the two

intermediate sub-petioles, mnnbers 2 and 3.

Kxporiinont '2S2

We sliall presently nnd tliat the responses
in the two cases are doini and up ; the record is obtained

Fig. 2H5 Record of responses due to stimulation of the diffei'cnt sub-petioles.

E, torsional responses under elcctrie stimulus; stimulation of 1, causes left-
handed torsion (up-curve) that of 4, a right-handed tor.sion (down-curve). L,
similar torsional responses under .stimulus of light. The records to the
extreme right show the rectilinear responses induced by stimulation of 2
(rapid down-movement) and of 3 (slow up-movement). Duration of a])plica-
tif)n (if light represented l)y two succeeriing arrows. { }fi})io.<ii.)

by attaching the short arm of the lever to the petiole and
removing the hooked glass support. In th^^ following
experiments we employ the moderate stimulus of light.

COMPLEX RESPONSE OF IMI. VIM'S t)9J»

The siib-petiole number "2 is first stimulated ; this causes a
rapid responsive fall, followed by subsequent recovery on the
•cessation of light. Stimulation of the sub-petiole 3 gives
rise to a relatively slow up-response ; the duration of apjili-
cation of light had, in this case, to be prolonged for obtain-
ing a moderate amplitude of response ; the recovery is also
relatively sluggish. These responses are seen in the third
pair of records given in Figure '2Go.

The results of experiments described above are delinite
and are as follows: stinuilation of sub-petiole 1, causes a
Jeft-handed, that of number 4, a right-handed torsion ; the
amplitudes of response in the two cases are approximately
equal. Stimulation of sub-petiole "2 causes a rajnd and
intense down-response, that of 3, a relatively sluggish and
less intense up-response. The effectors for these charac-
teristically different responses nuist, therefoi'e, be distinct ;
they must, moreover, be in conducting conniuniication with
the four sub-petioles in which excitatory impulses are
generated. We shall presently find that definite links of
^communication exist, between the points of reception of
stimulus and the distant effectors.

LOCALISATION OF NERVOUS TISSUE IN :\li:\10SA.

In my previous work, it has been shown that in Miinosa
stinmlus gives rise to an excitatory impulse, which is trans-
mitted with a definite velocity, that this impulse has all the
characteristics of the nervous impulse in animals.* The
most important problem in connection with this subject is
the localisation of the conducting or nervous tissues. I
succeeded in isolating a length of such a tissue in ferns and
was able to obtain with it many results which are regarded as
■characteristics of the nervous tissue in animals. In Mimosa,
however, it is impossible to isolate the nervous tissues

* Irritability of Plants, p. 1.54.

"00 LIl P, MOVKMKXTS IN' PLANTS

without iiijiir\ . jind I Ii;i\c. tor many ye;irs, Ixn-ri t'onfroiited'
with the problem of locahsin- in situ the particular tissue
which serves as the corKhictor of excitation. I have recently
been snccesslHI m in\ ctlorts. the method employed being
that of the l-'Jectric Tiohe, ah•(^•|(ly descrihod, by which it has
been |)()ssible to locah^e the geo-|;erc.>pti\ c layer in plants.

The princi[)le of the method will be understood if we
take the .somewhat analo;^()ns case of a cable alon^' which
electric messages are being transmitted. The conducting
strand is here embedded in a non-conducting sheath. We
can localise the embedded conductor, and pick up the tians-
mitted message by gradually thrusting in the b'dectric I'robe,
which is insulated except at the extreme tij>. A galvano-
meter included in the circmt of the Probe w^ill begin to pick
u[) messages that are being transmitted from the iTioment of
contact of the tij) of the probe with the conducting strand.
The dei)th of insertion lor contact can be read on a suitable
scale, and the position of the conductor may thus be
determined.

We may similarly localise the exact position of the-
conducting nerve end)ed(ie(l in the petiole of Mimosa (Fig.
2(\i')K J^xcitation of the snb-petiole will give rise to an exci-
tatory impulse ^\hich travels in a centrifugal direction
along the nei've. This excitatoi'v im|»ulse in the nerve is
tletected h\ an induced change of galvanometric negativity.
The conducting nerve will be most intensely excited by the
transmitted impuise, and the induced electrical change of
this |)articidar tissue will b^' maxiimnn. Excitation will no
doubt be irradiated to the adjoining tissue, but this will
undergo a rapid dinnmilion in ladial direc-tions outward^.
If the stitnulns be moderate or feeble the irradiation will be
slight.

The experimental procedure is as follows : — The Probe
is thrust perpendicularly to the diameter of the [)etiole (Fig.

coMPr.Kx rU':spoNSE of i-llvinls

701

266). The intrusion of the probe is by steps, say of 0.05 mm.
at a time. Tlie sh^ht wound j)rothic('(l by the insertion of tlie
tip of the probe causes an excitation, whicli subsides eom-
pletely in the course of about fifteen minutes. A sul)-
petiole is now stinudated by suitable stinudi. which may
be chemical, thermal, mechanical, or electric. The excita-
tory impulse is propagated [u-efeientiall\ along certaiii
conducting channel in tlu^ petiol(\ The results to be

Fi,<i\ 2t)H Tlif Klfclric I'rolio for Idea lisat inn of nervous tissue in i>Iant.'<
P, the probe in eireuir wirfi rlie <;'aivanonietex', tr ; S, tlie screw head, bv the
rotation of whieli the ])rf)he enters the petiole in successive steps : I, index
l)y which the (h']ith of intrusion may he fleterniined.

described were obtained with all the different modes of
stimulation. The electric method of stimulation has the
advantage that it can be maintained constant or varied in a
graduated manner. Special precautions are taken that
there should be no disturbance caused by leakage of the
stimulating current ; this is verified by the fact that reversal
of the primary current which actuates the secondary coil
causes no change in the electric response ; the excitatory

702 LIFK MOVEMENTS IN PLANTS

electric change in the different layers is, moreover, definitely
related to the character of the tissue.

I shall anticipate results by describing the characteristic
effects. The excitatory electric change, detectable in
different layers as the probe passes from the epidermis to
the central ])ith, is found to rise suddenly to ;i maximum in
the pjiloem jjortion of the fibro-vascular himdle; llie xyleiii
shows little or no transmitted excitation. Hence we arrive
at the conclusion, that it is tlie |>ldoem wliieh functions as

Fi;.'. 2ti7 M icri)-iiii(ito^'-r;i|ili sliowiim' a (|iia(l)'aiit of tlic jx'tiolo and the
■fibro-vascular biiiidle. 'J'lu' tissues seen in tlie section are : tlie ejiidcriiiis; C,
the cortex; B, the bundle sheath; J*, the tirst pliloeni; X, the xvlem; P, tlic
second phloem; and ji. the central pith. The dotted vertical line shows
<lirection of ])assajj:e of the I'lulie. {Mhudsh)

the nerve of the plant. T]\o cliaracteristic electric maximum
was not found in experiments where the probe missed the
phloem ; ;^ic;aler ex])erience now enables me to direct the
passage of the ]irobe so as not to miss the nei\c ti'act.

]n the (hagrau) of the transverse section of the petiole
of MiiiKisn, usually gi\'cn in text-hook, there is in each
bundle a single plilocin >tian(l outsid(> the xylem. 1 was,
therefore, con.sidciiihlv pu/./lcd hv the fact, that in ti'a\ei'sing
the bundle two electric maxima aii' obtained, one l)efore

COMPLEX RESPONSE OF PULVINUS 70:i

reaching the xyleni, and the second, after passing it. In
order to determine the cause of this anomaly, a transverse
section of the petiole of Mimosa was made, and differential
staining clearly brought out the fact that the phloem strand
is not single but double, one above, and the other, below the
xylem (Fig. '267) The second electric maximum coincided
with the inner phloem.

It may be stated here that in petioles provided with
four sub-petioles, there are Four distinct bundles with four
nerve trunks. The micro-photograph (Fig. 267) shows one
-of the bundles.

Electrical excitation in different layers. — I shall now

give detailed results of localisation of the conducting tissue.

The probe enters the epidermis and is pushed
Experiment 28.^ . £ a a- -^

m by steps or, O.Oo mm. ; it passes m

succession the cortex, C, the outer phloem, P, the xylem,
X, the inner i)hloem, P', and the central i)ith, p. The
thickness of the different layers is modified by age of the
rspecimen. In the records given below (Fig 268) the
electric response of the epidermis was + 12 divisions of the
oalvanometer. I have shown elsewhere, that the epidermic,
which protoplasmically is more or less dead, gives either a
zero or a positive, in contradistinction to the normal negative
response of living tissues. The probe at a depth of 0.1 mm.
encountered the cortex and the response there was - 17
divisions. We next arrive at the region of the phloem
which extends through 0.15 mm., the average depth
being 0.2 mm. The response in this region underwent a
sudden enhancement, as seen in the three responses - 61,
- 65 and - 40 divisions. The xylem, which was at a depth of
0.3 mm., showed no response, proving that it was a non-
conductor. When the probe reached a depth of 0.35 mm. it
encountered the second phloem, where the response under-
went a second enhancement of - 56 divisions. The probe
reached the border of the pith at a depth of 0.4 mm. and
the response underwent a diminution to - 26 divisions. In

704

[.Iir: M(t\ I.MKNTS IN I'l.ANTS

cases where the incident stinnihis on the sub-petiole is;
feeble, the irradiation effects are greatly dinnnislied : tiie-
excitatory transmission is then found otdy in the pidoeni.

Fiii'- -'i^ (JaKiiiiDiiietric record of t rausiiiitteci exoitatioii Iti (littVrcnt.
layers of the petiole: the Hrst is the positive resi)onse of the cpiilerinis, the
second is the feeble negative response of the cortex, the third, fourth, and
the fifth are the enhanced responses in the first phloem, the sixth shows
absence of excitation in the xylem, the seventh is the enhanced res]ionse in
the second phloem, the eighth is the diminished response in the pith.

I give below a sininriarv of ivsnlts obtained with ten different
sj)ecimens : —

TABLK LXII. — SHOWIXC INTKXSITY OF TRAXSMITTKI) EXCITATION' IN
DIFFERENT LAYERS IN TEX DIFFERENT SPECIMENS.

I'ransmitted e.'vcitation.

Itittercnt
la vers.

1

1 1 .

I.

IF.

III.

IV.

V.

VI. VII.

VFII.

IX

X . Mean.

Kpidermis ..

-1

0

0

0

0

0 0

+ 4

II

0 +it-.-,

tJortex

2

•.i

no

0

0

0 0

0

{)

0 .-,.-,

Phloem ...

:iO

:J0

-100

m

:m

44 :v.\ 18

20

—24 W ■)

.Xvlem

8

9

0

0

0

10 (1 ^4

-8

- 8 4 7

Phloem

80

;^o

84

10

.m

20 12 18 —2

W 2H 8

Pith

0

H

-•-'9

0

0

7 0 1 0

U

<• , 42

COMPLEX RESPONSE OF PULVINUS 705

It will be seen that in all cases the phloem is invariably
found to be the best channel for conduction of excitation.
Tiie following curve (Fig. "iGOt, plotted from tlie mean
values given in the Table TjXTI illusti'ates this in a striking
manner.

Tlic trcnisinittcd nervous iiiiindse. — The hhr(>va>ciilar
bundles, as stated before, are four in number, of which two
are vertical, one above the other, and the other two lateral.

^

Fig. 2H9 Curve showing the different intensities of transmitted exeitation-
in different hirers: E, epidermis : C, cortex : P, tir.'-t jihloem : X, xyleni ; P',
second |ihlocm : f>, pith.

In certain experiments the probe was passed vertically
through the petiole, when it encountered the upper and
lower bundles. I thus obtained maximum transmitted
excitations in the phloems of the upper fibro-vascular
bundle, and a similar maximum in the phloems of the
lower bundle, the intervening layers of tissue being practic-
ally non-conducting. From this it follows, tJiat excitatory
impulse is propagated alo}ig definite channels through the
length of the petiole.

'06

LIFE :\]OVEMENTS IN PLANTS

DI'.FINI IK INNEHVATION.

We sliiill now follow the nervous strands I'roni llie snh-
petioles to the motor organ. The excitation is conducted
along the phloem strand of tlio sub-petiole, and thence
through the connected phloem in the petiole. There are
four main hundU^s which vdtimatelv reach the motile organ,
the j)ulvinns. 'l'h(M(> the fihro-vascnlar hinidU^s a|)[)arently
fuse, hill \('r\ tine section of the ])ulviiius shows lines of
separation. (rW Fig. "274). The nerves thus terminate in

Fij.C. '270 J lie CDiii'sc ot lour uoi'voiis .-iii-aiKis t'rdin I lie tour .suh-jn'tioles to
tlie pulviiuis. 'J'lie lower tiffuro is a (liaj,'raiiiiiiatio section of tlie pulvinus
witli its four effectors. Effectors 1 and 4, whicli give rise to left- and right-
)ianded torsions are rcisjicctively in nervous connection witli sub-j)etioles 1
and 4. The lower effector 2 is connected with sulj-))ctiole 2, the response
))eing a ra])id down-movement. 1'1h> uppi'r (piadrant '.\ is in connection with
sub-petiole .3. tiie response licinu' a slow n |i-iiiM\cnuMit . {M iiiiii.--(i .)

the four effectors, of Axhich two arc lateral, the right and
the left; the other two, are upper and lower efl'ectors.
(Fig. -270).

The four (jiiadrants of tln' j)ulviinis are thii^ the four
effectors; eacli of A\Iiicli consists of a nerv(^ with the con-
tractile cortex. 'J'la^ nerve in effector ], is in conducting
communication with the siih-petiole 1 ; stimulation of that
sub-petiole causes excitation of the nerve in the effector ],
giving rise to the response characteristic of that effector,

COMPLEX RESrONSK OF ITLVINUS 707"

namely a left-handed torsion ; nervous stimulation of the
quadrant '2, causes a rapid down-movement; that of 4, a
right-handed torsion; finally, stinuiiation of the nerve in 3
causes a slow up-movement. The reason of the more
energetic down-movement of 2, relatively to the up-move-
ment of 8, is due to the fact that the cortex of the lower
quadrant is more excitable than that of 8.

The four quadrants have been numbered in the parti-
cular way to bring out their nervous connections with the
sub-petioles numbered from left to right. It might some-
times be more convenient to describe the quadrant 1, as the
left quadrant, the quadrant 4 as the right, quadrant 3 as the
upper, and quadrant 2 as the lower. The fundamental
reactions underlying the four types of response are now
fully understood ; these excitations may be regarded as
internal as far as the pulvinus is concerned ; for in the cases
described above, the pulvinus was not directly stimulated;
the excitation came from a distance and it is the four
stimulated nerves within the pulvinus, that caused the four
definite responses.

SUMMARY.

The pulvinus is a highly complex organ consisting of
four distinct effectors, each giving rise to a definite and
characteristic response.

The four quadrants of the pulvinus serve as different
effectors, each consisting of a nerve and a contractile tissue.

The four nerves in the four quadrants lead separately
to the four sub-petioles. These nerves have been localised
by the Electric Probe in the phloem of the four fibro-
vascular bundles in the petiole.

708 LIFE MOVEMENTS IN PLANTS

The I'our nerves in the four quadrants may, thus, be
separately stimulated by nervous excitation transmitted
from the four siib-))etioles, the resultirio- response beinfj
detenniiuMl by tlic (■li;if;ici(M-istic reaction of tlie pnrticnlar

•effcctoi".

Stiiuiilatioii of the iuM've in ibf upper (|iia<lr;iiit . liow-

■ever proihiced, is tlms rollowed by a Relatively slow iip-
movement ; that in the lower cjiiadiant, by a raj»i(l down-
movement. Stimidalion of the nerve i)i the left quadrant
gives rise to a left-handed torsion, that in the right

•quadi'ant, to a right-handed torsion.

i

LXI.— INVESTIGATIONS ON DIA-GEOTEOPISM

OF DORSI-VENTEAL OEGANS.

By Sir J. C. Bose,

Assisted by

SuRENDRA Chandra ])as, m.a.

The geotropic response in higher plants has been shown
to be bronght about by the differential excitation caused
by the falling starch grains, this differential action being in
some way due to the pressure of particles on the inner and
•outer tangential walls of the statolithic apparatus. It has
been shown further, that there is no specific difference in
irritability of the shoot and of the root, as is assumed by
the terms " negative ' and ' positive ' geotropism. These
terms are mere descriptive phrases which offer no real
■explanation of the phenomenon. The difference in the sign
of response in the two cases have been shown to be due to
the fact that in the one case, stimulation is direct, and in
the other, indirect.*

We have a iliff'erent type of geotrojiic reaction, described
AS ' dia-geotropic." A concrete example of this is foimd in
the motile pulvinus of Mimosa ; the leaf, under normal
condition, places itself in an approximately horizontal
position, the vertical lines of force of gravity being perpendi-
iular to it.

In the case of the so-called negative geotropism, a radial
fitem is found ultimately to erect itself so that its length is
parallel to the lines of force of gravity. If the stem is
rotated through 180°, that is to say, held in an inverted
position, it still erects itself as before. The organ has a

* Life Movements in Plants. Vol. II, p. 476.
709

710 LIIK .M()\i;.\[KNT8 IN PLANTS

definite reaction which is constant, whether it is held
direct ' or ' inverted.' Thoiigli the term ' negative '
geotropism does not explain the phenomenon, yet it is a
correct descriptive phrase; tlie organ places itself vertical,
whichever side of the organ faces upwards.

But the term ' dia-geotropism ' neither offers any
explanation of the phenomenon nor is it even a correct
descriptive phrase. It may he supposed that the reaction
is due to some unknown specific irritability which is charac-
teristic of the organ. If the Mi)ii<>s<i bo held in a normal
position, the motile pulvimis (with the iittached leaf) places
itself horizontally. But if the plant be held in an inverted
position, the leaf becomes erect, i.e., it assumes a ' negative
geotropic position. It is evident that an identical organ
cann*jt be endowed with both " negative " and ' dia-
geotropic ' sensibilities.

Detailed investigation on th<^ characteristic responses
of Mimosa leaf, not only under geotropic but under stimuli
in general, appeared to hold out hopes of throwing light on
the obscure subject, and of offering a rational explanation of
the phenomenon of dia-geotropism. The results of the
previous investigations have shown, that the pulvinus is a
highly complex organ consisting of a group of distinct
effectors; that these distinct effectors are actuated by di.stinct
nerves which had been localised. We shall presently find
that a definite mechanism exists by which the nerve in each
effector becomes stimulated under the stimulus of gravity,
and that such nervous stimulation in different quadrants
give rise to geotropic responses which are very charac-
teristic.

GENERAL DESCmPTION OF THE PHENOMENON.

Eeturning to the dia-geotropic pulvinus, one important

fact to be noticed is that the upper and the lower halves of

the organ are differentially excitable.

Experiment 284 -n ,i .-, t < • •-•

Further, the dia-geotropic position is
assumed by the leaves when its upper side is struck by

INVKSTKIATIONS ON i:iIA-c;EOTFWPIS]\[ 711

vertical lines of force of gravity, the direction of the hues
of force being supposed tt) lie the same as the (hrection of
the fall of a heavy particle. If now the plant he held
inverted, the more excitable lower half being struck by the
lines of force, the geotropic action is greatly increased and
the leaves place themselves i)arallel to the lines of force.
Figure 271 is the sketch of a Mimosa plant in a normal and
in an inverted position. In tlie former, the attitude of the

Fig. 271 Diagrammatic representation of the posture of leaves of
Mimosa in normal, and inverted positions.

leaves is dia-geotropic , and in the latter, negatively geotropic.
Another characteristic effect will be noticed in the inverted
position. The very young leaves near the top exhibit little
or no geotropic action. This may be due to the geo-per-
ceptive layer not being functionally developed in too young
a specimen ; evidence in support of this will be given later.
The third leaf exhibits the geotropic action in a
very pronounced manner, this leaf being erected
almost vertical. Still older leaves exhibit a decline
in geotropic action. Here, we have a result parallel to what

i\'2 I III. Mi>\ i;m|.;nis IN I'l.ANTS

Avas (ilitaiited wiih ilic petiole ol' 1' raiidcol ton , in wliich tlie
jiiiddle-a^ed liNives wvc loimd to he the most sensitive, while
the too yonnu and too old, the least sensitive to f^eotropic
stiuiiihis.

Anotliei' iiiterestini^ fesidt is the cUfNin^ upwards of the
Toiin;:;' shoot at the upper end ol the stem. \\'e thus have
in tlie same Miitiosd plant : (Da dia-;^eotropic response^ of
"the leaf in the normal position, (-I) a negative ^■eoti'o|)ic
res[)onse of the leaf in an inverted position, and (3) a negative
^eotropic response of the radial shoot. In the shoot it.self we
obtain, however, a transition from negative to dia-geotropic
response. Thus in a pro('iiml)ent stem, a ditlVMcntial excit-
al)ilitv is inihiced hy contimied action of sunlight on the
■t-X})osed uppei' side in eonsecpienee of which its excitahility
becomes reduced. The stem is no longer radial hut aniso-
■tropic. the shaded sid(» of the stem heing comparahle witl\
the lower half of the pulvinns ; siicli an anisotropic stem
■exhibits a dia-geotropic reaction.

The important characteristics of a dia-geotropic organ
Sive :(1^ that it cxliihits (litferential excitahility, the loirer
Jialf being rclatirclij the more excitable, and (2) tJuit tlie
4ia-geotr(ipic rrftponsc takes place whe7i the Uss excitable
half of the urtjan is struck by the vertical lines of the force
of yravitij. The dia-geotropic response is thus due to the
<hfferential action of the stimulus of gravity on an anisotroj)ic
organ.

CHARACTERISTIC RESPONSES OF PULVINUS TO STIMULIS OF

CRAY] IT.

We have seen in the last chaptei- how tlu» different
responses of tlie piilvinus. I'ight-iianded or left-handed
torsions, and u[»- and down-movements, are hroughl about
by the stimulation of each nerve in the h)ur effectors. Hence
if anv source of internal irritation causes a left-lianded

INVESTKiATlON.S <»X DlA-CKoTHOPlSM 71^

torsion, this can only be due to the^ stimulation of the nerve
in the left quadrant : siniilarly, right-handed torsion must be
due to stimulation of the nerve in the right quadrant, the
slow up-movenient, to the irritation of nerve in the upper,
and the quick down-movement, to the stimulation of the
nerve in the lower quadrant.

We shall iiow study in detail the characteristic responses
of the pulvinus uiider the stimulus of gravity. Here also
we find the four definite types of responses, namely, the up
or down, and the left- and right-handed torsions; these

: 0L_ b C ot

Fig. 272 Diagrammatic representation showing the four quadrants, in
(a) the upper, in (b) the lower, in (c) the left, and in (d) the right, sub-
jected to stimulus of gravity, G. The thick outline represents the more
excitable lower quadrant. The starch grains press against the nerve
respresented bv thick dot in each (piadrant.

are induced, as we shall presently find, by the effective
stimulation of one or other of the four quadrants by the
gravitational stimulus (Fig. 'Il'lK

Respo)}sr to geotropic stimulatiou <>t the upper a)i(1 the
lower quddnnits. — AYe hold the leaf in the normal position
sliglitlv inclined below the horizon, so that
the upper quadrant faces the Inies ot force ;'
and the response is a slow- up-movement. The leaf is next
held inverted so that the more excitable lower quadrant faces
the lines of force : the rectilinear response is now found to be
more energetic than in the last case.

714

l.ll'K .MOVEMI-'.NTS IN IM.ANTS

E.\i)eiimeiit 28ti

l!(si)0)isc to (icotrdjiic stiiiiiildtion of tJic left (uid the ri(jltt
qiKiditintft. — WluMi I lie pLiiit is so held that the left quadrant
is sid)]('ct to [\\c \eftical hues ol' force, the
response is by a left-handed torsion, followed
by recovery on restoration of tlie plant to the normal
position. Similar torsional response, this time in a right-
handed direction, takes place when the right cpiadraiit is
subjected to tlu' \ertical lines of force. l\ecords of torsional

Fiji'. 27;{ Kc'c-ords (if responses of the rijiht and k'fl (|uadr:iiiis to tli('
stiimiliis of jrravity. The re.spoii.ses are hy riiilit-liaiidi'd (dow ii-ciirve) and
left-liaiidt'd (ii|)-ciirve) tor.sioiis. [Mimosa.)

responses, right-handed and left-handed, induced hy gravi-
tational stinndns, are .seen in l''igni-e ■2'i'-\.

By subjecting the four (Hiadrants to the action of the
vertical lines of force we thus obtain tlie responses which
are characteristic of excitation ol the iierAc j)resiMi» in each
(|ii,i(iia nt . W'lial. llieii, is tlu' nieclianisni 1)\ which gra\ita-
tional force causes the irritation of the neixc in eacli
effector '?

In higher plants, it is the [)ressure of the heavy particles
which causes geo-perception and ihf suhsiMpient response.

I

INVRSTIGATIONS ON Dl A-OEOTIJi^PlS^r 715

The nieclianics of tliis is not yet fully iiiulerstood, but the
characteristic response of the pulvinus of Mi))iosa will be
found to elucidate the obscurity which surrounds the subject.
In regard to a satisfactory explanation of the characteristic
geotropic responses of the four effectors, it is thus necessary :
(1) to discover the statolithic apparatus in the pulvinus ;
<'2) to determine the precise manner in which the weii;ht
of the heavy particles excite the nerve in each of the
four quadrants and thus cause the response cliaiac-
teristic of the particular efl'ector,
(3) to discover the cause of the difference in the ^eolropic
reaction in the upper and the lower halves of the
organ, the upper undergoing a contraction and lower
an expansion. And finally, we have,
<4) to discover an explanation of the response peculiar to
the dia-geotropic organ. A radial organ is in
equilibrium when its length is vertical, but a verti-
cally placed dia-geotropic organ moves downwards
towards the horizon ; whereas, when placed inclined
below^ the horizon, it moves upwards, i.e., towards
the horizontal jiosition of e(|uilibi"ium.

THE STATOLITHIC APPARATUS.

In examining a section of the j)ulvinus, it was a matter
of great surprise and disappointment not to find any starch
grains, the pressure of which is the effective means of
geotropic stimulation. ^'et the geotropic response of the
pulvinus is more iironomuetl than in radial stems, in which
the presence of statoliths is such a -tiiking feature The
failure of detection of starch grains by iodine was afterwards
found to be due to the jiresence of chlorophyll bodies ; previous
treatment with chloral hydrate is, howevei", effective in
hringing out the starch grains in the cleaivst manner, lite
.starch-sheath is icnuuJ to abut direethj (»i the phloem of the

7 Hi LIIK. MOVEMENTS IN J'l.ANTS

four humllcs jinsriil in the jnilri h ii-s- . I'lj^iii-es "274. •27."), and
'i7() arc ic'|)r()(turtMl lioni plioto-niicio^i'aplis of transverse
•sot-tions ()(' (liiriMt'iit [iiihini and siciii. 'riu- first gives a
clear idea of tlu' arrani^eineiit ol' tour (|iiadrants in the
puKinns of water ?\Iiniosa ( Xcjiliinid (ilcrdccip , in Avhich the
cli>i»()sili(in (»r the. Four separate bundles and the starch-
sheath is similar tu that in Minuisa piKlicd. The section of

A^

^ t^

FIG. 27;

Fili'. 'J74 l^li()t(i-iiiicr(»ui-;i|)li nf t niiisv crx- M'ctioii of tlic iiul\inii> dt
Keptnido sliowiiiii' fdiii- distiiicl (|iui(lriiiils ; I juul 4 are lateral, 8 and ^ :iix'
ni)j)er and lower i-esiiect i\ely. Starch-sheath eoiitaiiiins;- starch gx-aius aVait
aji'ainst the i>h]()eiii.

Fig. 27o Enlarijcd iihoto-niicrouraiiii of the lowi'i- (luadraiit of Minmsd
■pudicci. K, ci)idiiiiis: C, sensitive cortex; S, starch-layer two cells thick
with miiiierous stareli-graius, which i)ress auainst the phloem, I': .\, the
xyloJii : (). pith. (The top represents the lower side).

the pnlviniis was taken near tlie p(>tiol(> and 'he loui- hinulles
are distinctly se[iarale(| Ifoni eacli other ([''ii:. "-I"!'. .\s
\ve approach inward--, the \{nw lunidle-- approach each other
and appear to form an almost coiitimH)n> rin;^ : each hmulle
is, however, physiologically distinct from its ncighhoins.
lOach (juadrant, //vw;/ oui to inirnrds. i> seen to consist:
(li of the .st'n>itive coi1e\. cJ' of the starch-

T\vi;sii(;.\r[()NS on i)i.\-(iK<)Ti;oi'i.sM 717

sheath ol' two layers of rells ^itudded with iiuuhmouk
stai'ch ii'rains. which imder orchiiaiy coiuhtioii,- Ave
dispersed chtlusely, hut tall on the lower sidr wIkmi
subjected to long continued ac-tioii of tlie i'orce of gravity.
The statocysts, as already stated, ahut directly against tlie
phloem of the bundle which functions as the nei've. We
have next the phloem, the xyleiii, and the central j)itli. Iiv
a very young pulvinus the starch grains are not lornuMU
which probably explains its insensitiveness to the stiniiiliis;
of gravity.

A transverse section of the lower quadrant of the
pulvinus of Mimosa pudica is reproduced, much enlarged, in
Figure 27.5. The characteristic distribution of the different
elements will be found to be similar to that in Nc[)tinii((.

Figure '276 shows the transverse section of the iijiper
side of the stem of hitpatiens, as representative of ordinai-y
dicotyledonous plants. The section was made after the
commencement of the upward geotropic curvature. ^^'e
observe the cortex, and a starch layer which abuts against
the phloem. The starrJi (jrains Jtave fdllen on tJtc lower
side and are practically pressing against the nerve. The
physiological machinary in an ordinary stem is, thus,
essentially the same as in the pulvinus ; the minor diffeience
is in the greater contractility of the sensitive cortex in the
pulvinus. But this is merely a question of degree and not
of kind: for we have seen that the cortical tissue in an
ordinary plant undergoes contraction under stimulation.
The real difference between a radial stem and the pulvinus
is this, that in the former, the excitability is the same alt
round, whereas, in the dorsi- ventral organ, the lower side
is relatively more excitable than the upper side. We shall
presently find, that it is this differentiation which causes
the <-haracteristic difference in the responses of dia-geotropic.
and negatively geotropic organs.

7 IS LIFK MOVEMENTS TN I'l.ANTS

The ^ootiopic t-iirvature lias been ex|)laiiie(l to be due to
<he joint effects of contraction of the upper, and expansion
of tlie lower side. We take a seedling' of EcJiptd, which is
found to he very sensiiive to <ieotropi(- action. It is laid
lioi'i/ontally, and a vertical section is made aftei- tlu^ proihic-

FiG. z:'<

HG. 27:

l'"ig. 27t) l'liut()-Tiiic-r(),iirii|ili of ti;iii>-\oi'sc .section of ii])iK'r side of sjeotropi-
eally curved Impafieits.

Note ttie starch grains fallen on t he inner taniientijil wall of statocysts,
S, prcssiiifr a^ain.st tlie phloem P. C, c<)rte.\ ; X, xvleni ; (), pitli.

Fig. 277 Vertical longitudinal sections of upper and lower sides of
gcotro])ically curved stem of h'rl'pta.

Xote contraction of the u])per, and expansion of lower cortex, 'I'iie starch
grains are ))ressing against the )>]iloeni of the u))i)er side and inducing
contraction. The starch grains in t he lower statoeysts are jiressing against
the outer tan<i(Mitial wall away from the |)hl<iem

tion of the Upward curvature. The illusli-ation (Fi^'. '277)
shows the physiolo;4ical chanj^es induced at the up|H'r and
lower sides. The cortex in the \i\ijxr side shoir.s a rchitlrc
contraction , irliiJr llnil in the iaircr nidc , a rchitivc, ('.rpansioii .
A single starch layer is seen to abut against tlie uppei" and
tlie lower nerves. I'lic slanli (ir<ii)ts in Uir iijij)! r slalnciist

INYESTICATIONS ON r)IA-r.EOTROPTS:\r 711.»

<irc found pressinij against tlte i}ni('~r tangential inill of the
veils nearest the pliloein ; in tJte lotrer side of the stei)i, the
■starelt grains in tJie cells are, on the other haud, pressing on
the outer tange)iti(d (rail furthest fro)n the phloem. It is
important to bear in mind thi^; characteristic difference in
modes of stimulation on opposite sides of the organ.

Returning to tlie j)ulvinus of Mimosa, the motile
apparatus has been sjiown to consist of four effectors, each
contaiiiiug a nerve. The excitation of each nerve causes
the response characteristic of the particular effector. We
.shall now inquire, how the nerve in each quadrant becomes
litimulated under the action of gravity, when that quadrant
is above and facing tlie lines of force.

In regard to the action of gravity, it is important to bear
in mind that the stimulus is internal. It is the weight of
the particles, the conjoint action of gravity and mass, that
exerts the pressure necessary for excitation. Fixing our
attention to one of the quadrants, say, the upper, held at an
angle inclined to the horizon and with its upper side facing
the lines of force, we find that the cells containing the starch
grains are practically in contact with the phloem which
functions as the nerve ; there is thus only a cell wall which
intervenes, and which is probably perforated and traversed
by protoplasmic threads. In any case, the nerve of the
upper quadrant becomes directly stimulated by tlie ])ressure
of the starch grains above, and the cortex of that quadrant
undergoing contraction gives rise to an up-movement.
If the pulvinus be held in an inverted position, the lower
quadrant faces the lines of force, and the responsive move-
ment is relatively more intense. This may be due to the
greater stimulation of the nerve by the pressure of a more
abundant or heavier starch grains, also on account of the
greater excitability of the lower quadrant. A large number
of sections of the pulvinus showed a greater abundance of

720 l,||-|-; MoVI'.MKNTS IN I'LVNTS

sliifcli-^l";niis ill tlir >t;itch---lii';il li of the lower (|il;uil"aiit .
This, jiloiii: willi the ,L;rc;it(M- cxcit.-iltilil y of tlic cortex expl;iiiD
the more intense ;ieot fo|)ic response of the lower (|n;i(li";int .
When the left (|ua(h';int is e.\[)()se(l to the xertieal line-> ot
force, the nerve in that (piadrant i)econies stimulated hy the
pressure of the particles, and the response is l)y a lel't-iiande(]
torsion, chai-acterist ic of the left elfector. Simihirl\_
exposure of the ri,iilit (|iiadrant to ^;ra \ ital lonal viiinulii^-
fjives rise to a ri^ht-handed torsion.

NMCA'i'ix'i': AM) posniNi'. i;i'. ACTIONS ON on'osrrr: sii»i:s oi'

A 1;A!)IAI. OI.'OAN.

The most perplexing problem in the geotropic action
is the difference in the sigr.s of I'eaction on the opposite side-^

l''i<<. 21S KttVcl of ftH'lili' stiinnlus in fiiliMiicinu- tin- nilr d' 'ji-Mwtii
Tlio curve nr tlie bt-siimiiii;- exliiliir.s tlic n(iriii;ii nilr : t'(H'l)lc ^t imulu.-
appliod for n sliort time eiiliiniccil t lie ikhiihiI imIc (h^ -cin in i lie oroct
curvf) followctl liy recovery.

of the or^an. \\'e have seen that the upper -^ide e\liil>ils
an excitatory contraction with diminution of tiiri:or. and
retardation of the rate of growth. This we ■-hall de>i;^nale
as the negative ivsponse. The I'eacti' n on the lower >ide
is, however, diametrically opposite, namely a positive
response, an increa-e of tnrgor. expansion, and (Mdiancemeiiti

INVESTK.ATKtNS OX l)IA-( ; IK tTKOITSM 721

ol tile r;it(' ol' growth. Al tiist sitilil tln'sc (([ipositf efVects
iiiuItT tlic idejiticid stiiiiiiliis of t^i'avity seem to \h- in-
explicable. I shall, however, be ai)le to adduce facts and
considerations which will fully ex{)lain the phenoiuen.-t,
which appear to be so anomalous.

Before entering into the detailetl study of this subject,
I would draw attention to the very important results obtain-
ed on the effect of intensity, and of point of application of
stinudus on ^To\\th (Expts. 8fi and 80, pp. '215-2-24, Vol. 1>.
It is there show^n, that while normal intensity of stimulus
causes a retardation, ^;ub-minimal stinuilus induces the
opposite effect of acceleration of growth (Fig. 278). Again.

Fiu. L'TVl Effect uf iuilircL-t and direc-t stiimihis on growth. Indirect
stinuilus at dotted arrow is seen to aceelei"ate. while direct stimulus at the
second arrow, to stop growtli. Direct stimulus in the present case has in-
duced an actual conti-action.

while indirect stimulus accelerates growth, direct stimulus
is found to hihibit it (Fig. 270). These fundamental effects
are demonstrated by application of different modes of stimu-
lation, and also by the employment of methods of record as
diverse as nie-'-anica! and electrical (cf. Expts. 85, 103).

Let us next consider the excitation caused by geotropic
stimulus on the upper and the lower sides of the organ. We
saw that the responsive movement is caused by stimulation
of the nerve by the ])ressure of the lieavy particles. Xow.
there is a characteristic difference as regards stiunilatiou of

722 JAW. MOVKMI-'.NTS IN PLANTS

the nerves in the upper and the lower sides. As already
stated, tlie particles exeit on tlic upper nei've a ))ressnre,
which is intense and direct, hence the upp(M- elTector under-
goes contraction. J-)Ut the case is (Utt'erent as regards stinni-
lation of the lower nerve. The starch grains in the
statocvst are seen to ])ress against tlie outer tangential wall
rui-lhcst Ironi the nerve (cT. l^'ig. -211). The stimulation
is thus indii'ect and minimal. Hence the I'esponse is
]>ositi\i', i.e.. an acceleration of growth. The lower effector
thus undergoes an expansion ; a change of growth thus
ocenrs which is of opposite sign to that in tlie upper effector.
The conjoint effect of c-ontraction at the uj)))er, and expan-
sion at the lower side hrings ahout tlie upward geotrojMc
^novenient.

DIA-OEOTROPIC T^RSPONSK OF THE PULVTNUS.

Tlie only question, which still remains to be explained,
is the dia-geotropic attitude of the leaf of Miinofid: in radial
-organs the position of geotropical equilibrium is vertical,
whereas, in the ])ulvinus it is aj^proximately horizontal.

A radial organ held \(M-tical remains in that position,
the length of the organ being parallel to tlie lines of force
of gravity. l>ut if the MiiiKisd plant be so placed that tue
leaf is vcM'tical. it does not rcMiiain in that position, but
moves (lownwai'ds till the uppei' half of the puUinus is
approximately ])erpendicular to the liiu^s of force. What,
tlien. is the un(l(M-|ying |)hysi()logical cause which would
jiccoimt loi' the characteristic dilfereiices of response in
i-adial and dorsi-ventral organs? The physiological difference
which we b)un.l in the two cases is, that in ladial organs
the excitabilitx of two opposite sides is the same; so that
similar stiimdation of the two sides producers similar contrac-
tions which connteract each other. liiit in the <lorsi-\ ent I'al
jiulvimis, owing to the difterenee of excitabilit v. the more

INVESTIGATIONS ON DIA-GKOTROPISM 72H

excitable lower lialf exliil>its iiiuler- the same stiiiinlatioii
a more proiioiiiued cuiitruction than the less excitable nj>per
half.

ELECTRIC INVESTIGATION.

I have already explained how the physiological c-han^e
associated with expansion or excitatory contraction of any
portion of the tissue may be detected by the concomitant
electrical change. We introduce the Electric Probe into the-
tissue in connection with a galvanometer. A positive
electric variation indicates an expansion, while a negative-
variation, the opposite reaction of contraction.

Geo-electric respoise uf radial organs. — We take the

radial stem of Tropaeolum, and introduce two probes on

opposite sides of the organ, a galvanometer'

Experiment 287 ... .... .^^^ . , .

being interposed m the circuit. vVe incline
the specimen at increasing angles, and observe the geo-
electric deflection : centering our attention to the electric-
change induced at the lower side we find, that the electric
variation thus induced is one of galvanometric positivity.
indicative of expansion of that side. (It is understood that
the electric variation of the upper side is negative, indicat-
ing" contraction of that side.) The inclination may be
continuously increased, and the electric change of the lower
side is found to remain persistently positive, though the-
intensity of reaction may undergo some variation. Inclina-
tion of a radial organ, thus, gives rise to an expansive
response of the lower, and a contractile response of the upper
side, and this throughout various angles of inclination.

Geo-electric response of the dorsi -ventral pulviuus. —

Electric connections similar to the above are made with the-

pulvinus of Mimosa. A necessary condition

Experiment 28S • ^ ■ / i j.i

for success of the experiment is to place the
specimen outside, exposed to diffuse light; the two connecting

^-' I.IKJ': MOVKMKNTS IN IM.ANTS

Wires are led to ilie galvanometer inside the hihoratorv.
It is iieeessary to take this precaution since lon;^ maintenance
of the ))lant in a dark room is apt to hrin^ ahoiii a condition
ot snl)-tonicity with conse(|ncnl disapj)earance, or even a
reversal, of the normnl response. After the electric connec-
tions are made in the niamuM- descrihed, the specimen is
adjusted so as to place the pnKinus and the nttached leaf
vertical. \\'ith a radial or;^an there i^ no cK^ctric ivsponse
in this vertical ])osition : hut the |>nl\ miis of M iiiidsn cxhihits
in this position a strong ^eo-electric response, the more
excitable (lower) half becoming- (lalvdnoinctricdllij iuujutivc.
in a tyj)ical t>xi)erimcnt the deflection was -45 divisions.
This ne{4'ative deflection of the mon- excitable side of the
(jr<.>an shows that a contraction of that side is induced in
the vertical position; the corresponding^ ;^eotropic resj^onse
tliiis tends to hrin^ (hjwn the leaf towards the hoi'i/ontal.
This, in I'eality, is what actually takes place.

The leaf is next inclined at an anj.>le of about .'i")° below

"the horizon. The geo-electric response is now found to

undergo a reversal, the moi'e excitable

Hxpci'imeiit 2K'.( , i ,. i • -71

half bemfi' now (idlnnioDictncdlhi pofntire
with a deflection of +•")<). Tlie specimen was next bi'ou^ht
back once more to the vertical position, with tlie restoration
of the original ^alvanometric negativity of the more
excitable side. The })ositivity of the lower side when in-
clined to -'1')° below the hori/.on indicates th;ii there is a
responsive reaction of expansion of the lower half by which
the leaf is raised towards the horizontal. There is thus a
transition tlirough zero, between the negative response in
the vertical. ;md the positive response at 35° below the
horizon : at this point of ti-;insi(ion. wIkmi the re.sponse di.s-
ap})ears, the leaf is in a state of ^eotropic e(juilil)riinn. This
is the dia-geotropic po.sition of the leaf which may be
regarded as apj)roximately horizontal.

investkkMions on l)lA-Gl•:oT^o^IS^r

725

We >liall next attempt to iliscover the reason I'or tlie
cliaiaLteristic ilifferences of response in radial and dorsi-
ventral organs. A diajiramniatic ivpresentation of a ;neo-
tr(jpic organ is given in Figure •i-s(), first in a vertical position,
then inchned at about ■\')° l)elow the hoiizon ; N and N' are
the two nerves at the opposite sides, the stimulations of
which, by the pressure of starch grains, cause the excitatory
contraction of the cortex of directly stimulated side, and the-

C SN ONS C

Fijr. 2S0 Diaf^rammatic representatiou uf a gootropic organ in a vertical
aiul in an inclined position. The shaded is to be the underside. It also
represents the more excitable half of a dia-geotropic orgran. C, C, cortei ;
S, S', statocysts. X, N nerves; O, pith. In vertical position of a radial organ
excitation induced by lateral pressure of starch grains is same on the two sides
in dia-gcotropic organs the excitation on the right side is greater (see text).

■expansion of the indirectly stimulated opposite side. The
side which is to be the under-side after inclination is repre-
sented as shaded.

Response uf radial organs. — As the starch grains become
piled tip at the base of the cell, they exert not only a vertical
but also a lateral pressure. Now in a radial organ held
vertical, the stimttlations of the two nerves are the same;
moreover, the excitability of the cortex at the two sides are
nho the same ; hence the two antagonistic reactions balance
each other. But when the organ is inclined, say, 35° below
the horizon, it is the upper nerve, as already explained, that
becomes directly and inteitsely stimulated ; whereas, the
lower nerve undergoes an indirect and feeble stimulation.

72tJ LIKK MOVKMl'lNTS IN I'LANTS

The result is a coiitractiun of the upper and an expansion
()(■ the lower side, this explains the upward or negative
geotropic curvature of radial organs.

Response of dorsi-ventral organs. — In tlie above dia-
gram, let us regard the right and shaded side to be also tlie
more excitable, in a vertical position of the leaf the lateral
pressure, exerted by the particles on the two sides, may be-
tlie same but the excitatory contraction of the more excit-
able cortex of the low'er half of the pulviinis will be relatively
greater. The greater excitation of the more excitable half
of the pulvinus in a vertical position is also demonstrated
by the induced galvanometric negativity of that side-
There can. tJierefore. I)e no balance, and the organ
moves dow'nwards. But at ;5r>° below the horizon, the
upper nerve N, becomes directly stinuilated by the pressure
of the particles, w-hereas, the lower nerve N' becomes feebly
and indirectly stinuilalcd. Tlu^ response is thus upwards,.
i.e., towards the iiorizontal position. The po.sition of
geotropic balance tlnis lies between the above tw^o extreme
cases.

This position of balance will evidently depend on the
differential excitability between the two halves of the aniso-
tropic organ. If the difference in the excitability is very
great, the dia-geotropic position will appioxiinate to the
horizontal. If the difference is slight, tlie balancing position
will be nearer the vertical, which is the normal position of
geotroj)ic e(iuilibiiuni in radial organs. The above consi-
deration will explain the different dia-geotropic attitudes of
various dorsi-ventral organs, in which the inclination to the
vertical is found to vary widely from an almost erect to ai
horizontal po.sition.

SUMMARY.

It has been shown that the stimulus of gravity causes
definite responsive movements depending on the particular

quadrant which faces the lines of force.

IWF.SIICATIONS OX DIA-GEOTROi'IS^^ 727

Geotropic stiiiiiilatioii is effected by tlu' j)ressufe ol starcli
grains in the statocvsts which (Urectly abut on the nerve.
When tlie upper (piach'aiu of tlie [xilvimis ol' Mimosa faces
the vertical hnes of force, the resnU is a moderate up-move-
ment ; exposure of tlie lower quadrant gives rise to a more
intense rectilinear-movement. Again, stimulations of
nerves of left and right quadrants by the pressure of
particles, give rise respectively to left- and right-handed
geotropic torsions.

The opj)osite reactions at the upper and lower sides of a
radial organ are due to the fact that the stimulation of nerve
at the upper side is intense and direct, whereas at the lower
side, it is feeble and indirect. The response induced by
moderately strong stimulus being a retardation of growth
and conti"action, the up{)er side becomes concave. The
effect of sub-minimvil stimulus at the lower side is an accele-
ration of growth and expansion, which induce the'
convexity of the lower side. The geotropic curvature of the
organ is thus due to the concordant effects induced at the
upper and lower sides.

A dorsi-ventral organ placed in a vertical position has
its opposite sides stimulated by the lateral pressure exerted
by the starch gi*ains ; the responsive contraction is greater
at the more excitable lower side of the organ. Hence the
organ moves downwards. At an angle of 35° below the
horizon, the upper half is subjected to direct and the lower
to indirect stimulation. The response is thus upwards,
towards a horizontal position.

The balancing" position between these extreme cases is
determined by the differential excitability of the two halves
of the anisotropic organ. This balancing position approxi-
mates to the horizontal wdien the difference of excitability
is great ; it becomes nearly vertical when the difference is
slight. These considerations explain the different dia-
geotropic attitudes of various dorsi-ventral organs.

VOLUME IV

MECHANICAL AND ELECTKIC RESPONSE
(^F PLANTS

I

LXII.— THE ])1A-HKLI0TK0P1C ATTITUDE OF
EEAVES.

By Sin J. ('. BosE,

Assisted 1)Y
Satyendha Chandtja Guha, M.Sc.

In the preYious chapter we ohtauied an explanation
of the dia-geotropism of Yarions dorsi- ventral organs, and
found that the effect was due to internal stinudation of the
nerve hy the pressure of starch grains. The diverse
responses of the pulviiuis, — by up or down movement, by
left-handed or right-handed torsion — were shown to be
brought about by definite reactions of the four distinct
effectors in the main pulvinus.

We shall in the present chapter describe investigations
on the phenomenon of dia-heliotropism.* In geotropic
response, the stimulus, as already stated, is internal; but in
heliotropic action, the stimulus is external. The heliotropic
movement takes place, not only when light acts directly on
the motor organ, but also when it acts indirectly at some
distance from the motor organ.

As a result of the effects of the direct and in,direct light,
the leaves adjust tliemselves in various ways in relation to
the incident light. The heliotropic fixed position is assumed
by means of curvatures and torsions of the motor organ,
which may be the pulvinus, or the petiole acting as a diffuse
pulvinoid. In some cases the motor organ alone is botli

""' cf. Rose and (Juha— Pvoc. Eov. 8oc. B-vol. 9.3. p. 153.

731

782 LIFE MOVEMENTS IN PLANTS

perceptive and responsive ; in others, the leaf blade'
exerts a directive action, the perceptive lamina and the
motor organ being separated by an - intervening distance.
This directive action of tlie lamina has been found by
Vochting in Malva verticilhttn . and by Haberlandt in
Begonia discolor, and in several other plants. In connec-
tion with this, it should be borne in mind that this charac-
teristic does not preclude the possibility of the motor organ
being directly affected by tlie stinniliis. In a nerve-and-
muscle [)reparation. the niuscK' is fxciti'd. not merely by
indirect but also by direct stinndus. As regards tlie Iielio-
tropic adjustment of lea\es. ilie stinudus of light acts, in
the cases just mentioned, botli directly and indirectly, t'lie
indirect -t inndation being due to some transnntted effect
from the peiceptive lamina. AA'e may legard tlie coar.se-
adjustment to be bi-on;ilit about by dicect. and tbe finer
adjustment by indiivct stiimdation.

Certain leaves thus assimie a iieliotropic fixed |)o>ition
so that the blades are [)laced at right angles to tlie direction
of hght, the directive action being due to certain transmitted
reaction, hitherto unknown. No explanation has, however,,
been forthcoming as regards the physiological reaction to
which this movement nmst be due. Suggestions have been
made that the dia-heliotropic position of leaves is of obvious
advantage, since this position assures for the plant the
maximum illumination. But such ideological considera-
tions ofl'er no explanation of the definite physiological
reaction. It is, moreover, not true, as 1 shall show in the
course of this paper, that there is something inherent in the
plant-irritability by which the surface of the leaf is cons-
trained to place itself ])erpendicnlar to the iticident light.

T have for many years been engaged in pursuing investi-
gation on the subject, and have recently .succeeded in
discovering the fundamental reaction to which the directive

THE DIA-HELIOTROI'IC ATTITUDE OF T.RAVKS 733

movement is due. I shall be able to show that the particular
attitude assumed by the leaves is brought about by trans-
mitted ■■ nervous impulse," which reaches the motor organ,
which is not simple but highly complex ; that there are
several distinct impulses which react on the corresponding
effectors grouped in the motor organ.

The dia-heliotropic phenomena, will be studied not only
in ' sensitive ' but also in ordinary plants. It will be
shown that the responsive reactions in both these cases are
essentially similar. As a type of the former I shall take
Mimosa piulica. and for the l.-itic^r. II iHiotilm^ aunnu.s.

GENEPvAr. DKSCiUPTlOX ol- THK l)IA-HELlOTR( )PIC rHENOMENA.

Before entering into the experimental investigation o^
the subject, it is desirable to describe the dia-heliotropifr
phenomena, as ty})ically exemplified by Minio.sd and
HeUa)ithus. A photogi'aph of the former is reproduced in
Figure •281 <;. in which the plant placed in a box had been
exposed to the northern sky and not to direct sunlight. Ir
will be seen that the leaves ^\•lli(•ll directly front the light
have been raised, and so placed that the sub-petioles, with
their leaflets, are at right rngles to the strongest illumina-
tion. The side or lateral leaves have, on the other hand,
undergone appropriate torsions — the plane of the leaflets
being adjusted perj)endic'ular to the light. It will be noticed
that in executing this, the petioles to the right and the left
have undergone opposite torsions. After the assump-
tion of this position, the pot containing the plant was
ttirned round througli ls()°. This brough^^ about a new
adjustment in the course of twenty minutes, the plane of all
the leaflets being once more at right angles to the light.
The new adjustment necessitated a complete reversal of the
former movements and torsions. Such perfect adjustment
is brought aliout l)y bright light from tlie sky. and not so

734 LIFK MOVEMENTS IN PLANTS

we\] by direct sinili-ilit . loi- ivasoiis which will be given later.
Jii Figure 'i'Sl ''. is sccmi tlie heliotropic adjustment of the

9-

Jeave.s of sunllower, gruwi) near a wall, ihe [ilani beinjj'

Tni', iiiA-iii'.i.ioi iKti'ic AiTi riDi'; oi' i.ivw i;s I'M)

expo.setl 1.0 liglit Iroin the wi'stfi'ii sky. TUc ,i(ljiistiii('iit is
essentially similar to that sihmi in Miiiiosa. The lateral
leaves, 1 and ."K haxc iiiuii'i'^^oiu* a|)|)i"o|)riate torsions — j'ijiiit-
huiuled or left-handed — so tliat the leal'-hlades placed
themselves at ri^Iit angles to the light. The leal' nmnhered
li has l)een raisc^l. j)laeing its lamina perpendicidar to the
light. A e()ntril)nting factor in this is the l)ending over of
the stem, due to positive heliotro})ic curvatnre. \\hich
accentuated the I'ise of the leaf nnmher -2. The same
beudiug ol'len causes an apparent fall oi' the leaf marked 4.
When the stem is tied to a stake, the bending over of the
stem is prevented : the leaf mnnhered "2 is then found raised
by heliotro|)ie action : hut there is little or no lall of the
opposite leaf.

Another photogra|)h is reproduced (Fig. -ISlc) of the
heliotropic curvature and adjustment of a different species of
sunflower, which was grown in the open. In the morning
the plant bent over to the east and all the leaves exhibited
appropriate movements and torsions. In the afternoon the
plant bent over to the west, all the j)revions adjnstments and
torsions being completely reversed. The plant contiiuied to
exhibit these alternate swings day after day till the. move-
ment ceased with age.

CH.AlJACTP^niSriCS OF THE MoToH OJKiAN.

I have shown elsewhere that there is no essential'
difference between tlie response of " sensitive " and
" ordinarv " })lants. 1 shall now show that all the charac-
teristics of the response of the leaf of Mi)n<)S<i are also fonnd
in the leaf of Hrlianthiis. These will be specially demon-
■strated as regards normal response and recovery, the
response of adaxial and abaxial halves of the organ to
stinnilus, the effect of direct and indirect stinmhis in inducing

I'M) LIFK MOVEMENTS IN PLANTS

heliotropic curvature, the daily jieiiodic movements of the
leaves, and the torsional response to latei'al stimulation.

MKCHANICAI, IIKSCoXSH DlKTo i)l KKKKKN 11 Al. I'.XC IT AllI I 11 Y .

It has already been explained thai on account of Ijie
differential excitability of the uiipcr and lower haUcs of ijic
pulvinus, a diffuse stimulus causes a responsive fall of the
leaf of Mi}HuS(i. I shall now show that a similai' reaction
takes place in 1 1 clldiitlins.

In 1 1 < liitiitlilis , the entire petiole acts as a motor oi\uan,

of which the iijiper half is relati\i'l\ less excitable. hilVusc

stimulation l)\ electric shock inducer a
Experitiiftii .".sn • ,• n ,• n i • i

responsive lall. lollowed by a ivcoverv on tiie

cessation of stimiihi.-^. The response-recoi"ds thus obtained

are \ov\ similar to those obtained with the leaf of Miinosa.

In Uclldnllius the reaction is relati\(dy shi;iL;ish and the

coJitraction is not .so ^reat as in Miiimsii. The ditfereiice

between the two responsiw reactions is one of de;iree and

not of kind.

HKSl'ONSK To SI IMI LA'lloN Ol- .\I)\XI\I. AXD AH.XXIAI.
, HAl.\i:s ()!• 'IHI-; OIM.AX.

The upper hall of the pid\inii^ of Miiinisd respond.-- to
a[)plicatioii ol' li;^lit by local conlract ion : the U>af is thus
erected an<l the mo\enicnl towariU li;^ht ma\ be described
as positive lieliotro|)ism. The leatlels attacluMl to the sub-
petioles are thus made to face tlu- lij^ht. ruder stroiij; and
lonf^ continued sunlight the e.vcitation is transmitted across
the pulvinus. and causes at first a neiil lalisat ion . and finally
a reversed or iiej^atixe movement by the contraction ol the
more excitable Icnver half of the organ. This is the reason
why tile dia-heliotropic adjustment is less perfect under
strong sunlight.

THK l»I A-HKMontoPU; ATTI'll'DK oK LEAVES 787

We t)l)t;iin p.iialU'l reaction with tleliaiithiis ; Ikmv the

petiole acts as an extended j)u!vinoiil. Iji^ht apj)lie(l liom

ahove, causes an erectile nioveiiient : when
E.\i)ennieiit "JiH i- i i i

apfuied below it causes a more energetic

down niovenieht. As the transvei'se conductivity of the

petiole is I'eehle, the positive lielioti'0[)ic res[)onse, induced

by h^ht acting IVoni above, is rarely reversed into neg'ative.

THE MECHANISM OF HELIOTIJOPIC CURVATURE.

.V few words iiia\' now be said of the mechanics of
curvatuiv !)>• which the stem of IJ cliinifhu^ l)en(fs to^\•ards
light. All forms of stimidi. iiu-ludiiig that of light,
induce a diminutit)u of turgoi- and conseciuent con-
traction, and retardation of the rate of growth of the directly
excited side. But this is not the onl\ factor in bringing
about the positive ctu'vature. 1 have sIkavu that wliile the
effect of direct stimulus at the proximal side of the stem
induces diminution of turgor and contraction, its effect on
the distal side, where it acts indirectly, is the very opposite,
namely, an increase of tiu-gor and expansion. The positive
curvature is thus due to joint effects of direct and indirect,
stimulus at the two opposite sides. 1 have been able to
demonstrate the induced increase of turgor at the distal side
bv experimenting with tlie stem of Miniosa. The stimidns
of light is applied at a ])oint directly oj)posite to the motile
leaf, which by its movement indicates the change of turgor,
the induced increase of turgor brMUg indicated bv an erection,
and diminution of tia-gor bv a fall of the leaf. Aj)plicatien
of light at a point on one side of the stem was thus found
to induce an increase of turgor at its diametrical I v opposite
pcMut, as evidenced by the erectile movement of the leaf.

Parallel experiments which 1 have recently carried out
with Hc'Uantltus gave identical results. Arc light was
continuously applied at a point opposite the indicating leaf;

788 LiFK M()Vi;.mi:nis ix i'i.antr

1iiis imlnccd ;ni iiici-easc of iiirgoi', as exliibitcd l)\ a con-
tinnoiis erection of tlie leaf. We thus find that wliile direct
stimulation induces a diniiniition of turj^oi- at the proximal
side, indirtMt stimulation causes an increase of tui'^or at tlu'
(Ustal side. The positive hehoti-opic curNaturc is thus Ain'
to the joint ett'ects o\' contraction of the proximal and
•expansion of the distal side.

1 Ml-; DIlKNAl. .\1()\ I.MI'A'r.

The daily pei'iodic movements of the leaf Minto.'ia and
of Ilrliaitthits exhibit a further similarity which is remark-
able. 1 have shown i^lscw here* that in ])lants sensitive to
li<:ht the operati\(' factors in the diui'nal movement are : —
<i. Tlie vaiiation oi' j^eotro))ic action with chan^in^ tem-
{)erature. A rise of temperature is found to inhibit tlie
l^eotropic action: a fall of temperature accentuates it. In
conse<|iience of this the leaf, subject to j^'eotropic action,
undergoes a periodic up-and-down movement ; the niaxinnnn
fall of the leaf takes place at thermal noon, which is about
•2 T'.M.. the maximum rise is at thermal dawn, about 0 \a\.

h. The action of li^^ht is, ^encr-all\ speakin;^. anta-
gonistic to that of tem|)eratiue. In the forenoon, rise of
temperature cau.^es a hill of the leaf, but continuous li^ht
acting from above tends to raise it. The rapid diminution
of li^ht towards evenin«4 acts virtually like a stimulus,
•causiii;^ a II ;d)lilpt fa II of t lie leal .

The diurnal movements of Miniosa and IfrlidHilnis
exhibit four phases which are vei-y similar : -

iji The leaf, o\\iii;i to fall of lemperatuiv erects itself
from -1 to .V."i(l CM., or thi'icaboiits.

(•Ji After (■) I'.M. there is a rapid dimimitiou of li;4'ht,
and the le;if iin«ler^()es a sudden hill, which c()ntinues till
about i» J'.M.

* Life Mm\.iikii18 in Plant.s, Vol. 11., 1>. 'lOT.

THH ItlA-Hi;i,l()i KoI'lC \ITHriiK ()V T.KAVKS 739

(H) Alter *.) r.^\. the U-af lie^iiis to t-ret-t itself with the
fall of teinpenituiv. the iiiiixiimiin erection heitig attained
at thermal dawn, which is at (l a.m.. appi-oxiniatelv.

(4) In the forenoon the leaf is acted on by two anta-
gonistic reactions, the effects of risinj^" teniperatttre and of
increasing' light, the effect of rise of temperature being pre-
dominant. The leaf thus contiinies to fall till thermal noon,,
which is ahoiit 2 P.M.

TORSIONAL RESPONSK To I.ATI'LRAL STniULUS.

When the nerves of the left and right tiaidvs or
quadrants of the pnlvinns of Miiiiosd aiv stiniitlated by
excitations transmitted from the left and right sub-petioles,
there are produced left-handed and right-handed torsions
(see Fig. -265). We also obtain similar results through
direct stimulation of the left and right flanks of the pulvinus
by light. Direct stimulation of tlie left flank induces a
left-handed torsion ; that of the right flank, a right-handed
torsion .

The response just described above takes place when the
pulvinus is exposed to lateral light, the leaflets carried by
the sub-petioles being completely shielded from it. The
differentially excitable organ thus undergoes a twist, in con-
sequence of which the less excitable upper half of the
pulvinus is made to face the stimulus. The leaflets attached
to the sub-petiole are thus carried passive!}', like so many
flags, to face the hypothetical source of light. It is obvious
that the response is brought about by a definite physiological
reaction and not for the utilitarian purpose of securing
maximum illumination of the leaflets or the lamina.
Teleological considerations, often adduced, offer no real
ex}>lanation of the jilienomena : sucli arguments are,
moreover, highly misleading, for similar responsive torsion
is induced, not merely by light, but by modes of stimulation:
so diverse as electrical, thermal, geotropic, and chemical.

740 \A\'\: .\U)\ i:mivN'is in i'lants

'lorsiottal rc.sitoHftc of petiole of Heliantlins. — The above
results are also exliibitcd l)y the ixMiolc of H rlifnilliiis iiodor
various stimuli applied l;Hci;dl\.

Two fine pins are thrust about 1 cui. a[>art on the ri^ht

Hank of the petiole of II (li(uitliu.'<. to s(n've as electrodes for

application ol' indnction shocks IVoin a
ExperiiiRMit -J'.*--' . • ,• i ,

secondarv coil ; a siuuiai' pair ol clcdrodes

are attaclied to the left flank. On application of a leeble

l'"i^'. i;si; ■rorsioiiiii r('s))()iisc ol' petiole of Heliaiithus in ri'sponse to
(n), electric stiimilus, and {b), to stiiiuiiiis of lif^ht. R and \j are the opposite
responses, due to stimulation of the rij^ht and left flanks. Successive dots
are at intervals of 20 seconds. The ))roloTi<;ed latent jieriod under li<rht is
not shown in the i-ecord. The )>ortion of record exhitiitinv recovery is also
omitted. The two thick dots in (b), rejiresent thi' moments of cessation

n( liirht.

tetanising shock to the ri<:lit Hank, the petiole (Exhibited a
ri<jht-handed torsion ; stinni'ation of the left flank induced a
left-handed torsion. Electric stinnilation quickly stirs up
the internal tissue, hence the latent ])eriod is short, and the
responsive reaction is rapid (Fig. 282r;i. 1 next took a
<lifferent specimen, and ap|)licd Ihe stimulus of li^ht to the
right and the left flanks alternately. This gave rise to right-
and left-handed torsions as under electric stimulus, the only

IHI". niA-IIKl-lOlKolMC MTrilDK oF I.KAVKS 741

<litterence being in the slower reaction and prolongeil latent
])eri()(l of lo rninntes (Fig. •2S'2b). It must be remeni-
lificd iliat i:i the case of light the exeitation is gradually
iiansiiiitted lioni the outer surface to the inner tissue.
As regards the direct action of light, the results given above
show that the responsive reactions of sensitive and ordinary
plants are not different, but essential!}' similar. With
reference to the heliotropic adjustment of leaves, we found
that, W'hen light strikes synnnetrically in front, the leaf
bends towards it. The growing stem itself is excitable, and
its induced curvature is a contributory factor in placing the
.surface of the lamina at right angles to the light. 1 weaves
struck laterally by light undergo torsion which is definite,
being determined by the direction of the incident light.
The torsion thus induced places the leaflets or the lamina
at right angles to the light. These effects are produced, as
stated before, when the responding pulvinus or petiole are
directly exposed to light, the leaflets or the lamina being
protected from it.

The heliotropic adjustment of leaves often takes place,
as we have seen, when the motor organ is in the shade, or
is artificially kept so. There must, therefore, be trans-
mitted impulses by which the distant motor apparatus is so
actuated that the leaflets or the lamina are placed at right
angles to the light. The transmitted impulse, if single or
<liffuse, cannot evidently exert the necessary directive action.
1 have already explained (p. 706) that the transmitted
impulse is of a nervous character, that the impulses are
more than one, and distinct from each other, and that they
travel by different channels from the lamina which perceives
light to the distant effectors where movement is produced in
response to transmitted excitation.

THE DIRECTIVE ACTION OF PROPAGATED IMPULSE IN
HELIOTROPIC LEAF-AD J U STMENT.

As in Mimosa, so also in Helianthus, the nervous
channels were traced from the receptor to the effector. The

742 TJFF. MOVKMF.NTS IN PLANTS

most difficult {)r()l)l(Mii tlmt conrroiits iis now is to cxphiitf
the responsive inoxt'inciit ;itul lotsion of the motor or^^aiu
by which the expaiulcd Icar-siii-race laces the ii^^lit. I shall
now desc!"il)C the motor icaction wht'ii (litrcicnt parts of the
leaf are locally stimulated, not oidy hy li^ht. hut hy diverse-
modes of stimulation.

Hl?:LIOTl!()t'TC \l).irs'rMI>:N'l' ()!•' 'I'tll'. I.IvVI' ()]■ MIMOSA.

I lia\e already shown ( l'',\periments -JSO, •2(Sl ) that
stinndation of the ri^lit suh-petiolc hy induction sJiock or
bv li^'ht induces a rij^ht-handed, that of the left sub-petiole.
a left-handed torsion. We shall considt-r in detail tlu-
effects induced hy vertical li;:lit on leatiets of Mi)ii(>s(t.

When the leaflets of the ri^ht petiole were acted on
b\- vertical li<:'ht. the distant puUimis nndcrwciit a toi'sion.

and the amount of ii.Liht ah^orhfd hy the

E.xi)eriiiiciit 'J'.'."" , ,, , , ,1 • ■ •, ■

leaflets thus hccamc rfdnecd. Ilcnce it is

obvious that it is not the advanla;^e of the plant, hut the
inevitable physioloj^ic-al I'eaction, that detenuines the move-
ment. Stimulation of the leaflets of tlu^ left suh-petiole
induced a left-handed torsion. If the leaflets of the two
intermediate sid)-j)etioles are kept shaded, and the leaflets of
the right and left sub-petioles arc illuminated hy xcrtical
light, the two resultin<4" torsions arc loimd to balance each
otlier. While in this state of dynamic balance, if the
intensitv of li^hi on one of the sub-petioles, say the left, he
diminished by interposition of a piece of paper, the balance
is at once upset, and we find a ri^uht-handed torsion. The
movements caused by transmitted excitations from the inter-
mediate sub-petioles nundier -2 and number 3, similarly
balance each other. It is thus seen that equilibrium is only
possible when the entire leaf-surface is equally illuminated;
and that would be the case when the surface is ])erpendicular
to the incident li^lit. The ('ia-heliotropic attitudes of leaves

THE DIA-HELIOTROPIC ATTITUDE OF LEAVES 743

is thus brought about by distinct nervous impulses, initiated!
at the perceptive region actuating the different effectors.

TRANSMITTED EXCITATION IN HELIANTHUS.

In HeUanilms we can distinguish three main veins or
nerves, which gather excitation from different regions of the

Fig. 283 The upper figure is a diagram of stimulation of nerre-ending of
Helianthus. The record below shows that stimulation beyond the cut gives
(rt), no response; while stimulation at (6), induces right-liandcd torsion.

lamina. The nervous function of these are demonstrated
by two different methods of investigation, electrical and
mechanical. In Helianthus we notice three main nerve-
endings in the larnina in continuation of the nerves in the
petiole (Fig. 283) the petiole itself serves, as we have seen,
as an extended motor organ.

714 LIFE MOVEMENTS IN PLANTS

■Method of electric response. — One electrode wag
pricked in so as to make contact with the phloem of the

ri^lit buiulle embedded in the petiole; the

fc^xperinient 294 , ^ , ■ ■ ,• ,

second coiitact was riKidc \\itn a distant

indifferent point. ]^^lectric stimulation of the right nerve-
termination in the lamina gave rise to an electric response of
galvanometric negativity, the response being monophasic
Application of thermal and chemical stimulations produced
siitiilar residts. In tlu^ \\\n last cases, the intense stimulus
gave rise to multiple responses. ]n the next experiment

Fi)^. 384 (talvanomeiric record oF transmitted excitation in the nerve of
HelianthuK. The first is in resi)onse to electric stimulus, the second and the
third to thermal and chemical stimulus. The fourth is a diphasic response.

Note the multiple response due to strong stimulation. [See text].

both tlie electrodes leading to the galvanomet-er were
•connected witli the nerve in the petiole, 1 cm. behind the
other. The response was now diphasic, since excitation
reached the two points in succession. (Fig. 284).

Method of MecJianienl Response. — The effect of trans-
mitted excitation was now oliserved by characteristic
responsive movement ot the petiole, which i< tiie motile
organ. The stimulation employed is electrical and photic.
The electrodes for induction shock are inserted in the
manner .seen in Fig. 283.

THE DIA-HELIOTROPIC ATTITUDE OF LEAVES 745

Electric stimulation; effect of discontinuity. — A cut is
made between a and h, thus interrupting the continuity of
the ncive to tlie right. Electric stimula-
tion at a induced no responsive movement ;
Btimulation at h. however, induced the normal response by
right-handed torsion (see lower record, Fig. '283).

Altrrnate Electric Stimulation. — The right and lett

Experiment 295

Fig. 2S."j T()r.sional rcsjionsc due to transmitted excitation in Helianthus ;
(a), right-handed torsion due to electric stimulation of the nerve-ending in
the right half of the lamina ; (b), right-handed and left-handed torsions due
to transmitted excitations caused by alternate illumination of the right and
loft half of the lamina. Light was stopped after the thick dot.

nerve endings in the lamina were stimulated alternately.

This gave rise to right-handed and left-
Experiment 296 1 -, J . • , . , T ^

lianaed torsions respectively. in tigure

l285a, is given the record of right-handed torsion.

The following experiments will show that photic
f^timulus induces a reaction whicli is similar to that of
electric stimulus : —

Stimulus of LigJit. — Hunlight was thrown first on the

right half and then on the left half of the lamina. The

transmitted excitations induced correspond-

Expeiiment 2'.t7 . . nnrL\ a

ing torsional responses (.rig. 2o5o). A

balance was produced when the two halves of the lamina

74(j LIKE .MOVEMF^NTS IX IM.ANTS

were simultaneously exposed to equal illuiiniiation. Here
also, as in Mijiiosa, the heliotropic adjustment is hrouj^ht
about by balanced reactions of the different cftectors.
; The movement of a dia-heliotropic lamina has heert
figuratively, compared with the movement of the human eye
by which it points itself to a luminous object. It is strange
that there is more truth in this comi)arison than was
suspected. In describing the rolling of the eyeball Bayliss.
says : " When there are two sets of muscles acting on a
movable organ, such as the eye or a part of a limb, in such
a way that they antagonise one another, it is clear that for
effective performance of a particular retiex movement, any
contraction of the muscles opposing this movement must be
inhibited. Further, the inhibition of one group must
proceed pari passu with the excitation of the other group
to ensure a well-controlled and steady motion."*

Now, in the torsional adjustment of the leaf due to
unequal stimulation of the two receptors — the right and left
halves of the lamina — let us take the extreme case where
one half, say the right, is alone stimulated, either by light
or by electric shock. The two effectors for torsional move-
ment, the right and the left, are the responding tissues in
the right and left flanks of the petiole. These are actuated
by the nervous impulses transmitted along the two conduct-
ing strands. When the right half of the lamina is stimu-
lated the transmission of excitation along the conducting
rstrand on the right is detected (Experiment 294) by an
electric change of galvanometric negativity, and the corres-
ponding mechanical response of the right effector is, as
shown before, by a right-handed torsion. We may next
inquire into tlie nature of the transmitted impulse along the
left flank of the {)etiole concomitant with the excitation of
the right half of the lamina. It is obvious that a similar

* Bayliss— Principles of General Physiology— 1915, p. 494.

THK DiA-HlilJOTIJOPJC ATTITUDE OF I.KA\ ES 747

■excitatory impulse on the Jeft tiaiilv (the electric indication
of which is galvanonieti-ic negativity) would oppose and thus
neutralise the particuiai- directive movement. Hence lor
•ensuring" a^ steady directivi> motion, in response to stimula-
.tion of the right half of the lamina, all excitatory impulse
to the left llaidc of the petiole sliould he inhihited. Further,
the directive movement induced hy the stimulation of the
right half of the lamina would he actively helped if the motor
reaction of the left tlaid< of the jjctiole he of an opposite
character to that in the right tlank. We found that the
right-handed torsion is induced by a differential contraction
of the right flank and for concordant effect the reaction of
the left tiank should he opposite, i.e., a differential expan-
sion. The nervous impulse which actuates the right
•effector when the right hall' of tlie lamina is alone stimidat-
ed, is indicated by galT(nt<i)H(iric negativity ; for concordant
movement under the above condition, the impulse which
.actuates the left effector should be of opposite sign, i.e., of
■galvanonietric positivitij.

I carried out two sets of experiments on the above lines
•Avith an identical leaf Helimitlnis. For electric detection of

transmitted excitatory impulse, along the
Kxpariment 29 . ,

right nerve, one of the contacts was made

with that nerve, the second being with a distant indifferent

pohit. The nerve endings on the right half of the lamina

Avere electrically stimulated and the transmitted impulse

along the nerve gave the usual excitatory reaction of galvano-

metric negativit}^ A second pair of contacts were made

for detection of transmitted impulse in the nerve of the left

liank of the petiole. Stimulation of the nerve termination

of the right half of the lamina gave in the left nerve a

reaction of gaJvanomrtric positivitij. In practice stimulus

was always applied to the right half of the lamina, and

galvanometric connections were made alternately with the

748 I.IIK MOVEMENTS IN PLANTS

right and left nerve. Tlie results wen- always the same and
showed that excitation of a nerve gave rise to an opposite-
reaction in the contiguous nerve. There is no douht that
these two nervous impulses of opposite signs reaching the
antagonistic tissues of the two flanks of the motor organ
must be of importance in the co-ordination of the resulting
movements.

SUMMARY.

In certain leaves the lieliotropic adjustment is brought
about by transmission of nervous impulse to the motor
organ. A continuity is shown to exist in the respon.se of
sensitive " and ordinary plants. Mimosa pudiea is taken
as a type of the former, and HcJiantJius (uuinus of the latter.
Mechanical response is brought about in both by the-
differential excitabilit\ ol' tli^' upper and lower halves of the
motile organ. 'IMie lower lialf in both is the tii()r(> excitable.
Local .stimulation of the abaxial half of the organ induces an^
erectile movement, that of adaxial half a more raj)id dow'n-
ward movement.

Heliotropic curvature of a stem is (lu{> to the joint effects
of contractile reaction of the proximal a7i(l expansion of t}u>
distal side.

The daily periodic uioxements of the leaves of Mi)ii()f;a
and oC H eliantlivs are essentially similar. The diurnal
movement is brought about by the variation of the geolropic
action with changing temperatme, and by the varying in-
tensity of light. The leaves erect themselves diu'ing the
fall of temperatuie from tli<M'nial noon al •! r.M. to about
")-,■{() P.M. Owing to the rapid diminution of light in the
evening the leaves undergo an abrupt fall which continues-
till '.) P.M. .\fter tins the leaves erect themselves, till the

THK DIA-HELIOTKOPIC ATTITUDE OF LEAVES 741>

maximum erection is attained at 6 a.m., which is the thermal
dawn. The movement of the leaves is then reversed and
there is a continuous fall till the thermal noon at 2 p.m.

A very important motile reaction in the adjustment of
leaves is the torsional response to lateral stimulus. The
following is the law which determines the directive move-
ment : An anisotropic organ when laterally stinmlated hy
any stimulus undergoes torsion by which the less excitable
side is made to face the stimulus. In a dorsi-ventral organ
the upper side is, generally speaking, the less excitable side,
and the response of such an organ to lateral stimulus may
be expressed in the following simple terms. Lateral
stimulation of a dorsi-ventral organ induces a torsioji which
is right-handed, when the right flank is stinmlated. T.eft-
handed torsion is induced by the stimulation of the left
flank.

The effects described above take place by direct stimu-
lation of Hght. They also take place under transtnitted
excitation.

The pulvinus of Mimosa may be regarded as consisting
of four effectors ; the response of the right effector is by a
right-handed torsion, and of the left effector by a left-handed
torsion. The upper and lower effectors respond by rectili-
near up-and-down movements.

Excitation at the receptive region is propagated along
a definite conducting channel, which is traced from the
receptive area in the lamina to the corresponding effector in
the motor region.

In a petiole of Mucosa, provided with sub-petioles
carrying rows of leaflets, stimulation of the right row of
leaflets by light gives rise to an excitatory impulse which
reaches the right effector and induces a right-handed torsion.
Stimulation of the left row of leaflets induces the opposite,.
or left-hanced torsion. The illumination of the second

750 LIFE IMOVEMENTS IN PI>ANTS

sub-petiole intliices an up-iiioveineiit ; that of llie tliird siih-
petiole a tlowii-movenuMit. Tlio leal' is thus adjusted in
^pace by the co-ordinated action of four reflexes, equilibrium
jein^ attained when the leaf-surfaces is perpendicular to the
incident light.

Tlie dia-heliotropic attitude of leaves is thus brought
about by distinct nervous impulses initiated at the perceptive
region actuating the different effectors.

Eesults similar to the above were also obtained with
HeJianthus.

For the movement of the eye the contraction of the
..'Uiscle opposing the movement has to be inhil)ite(l. In
the torsional movement of the leaf, it is found that the
stimulation of one nerve causes in a contiguous nerve an
opposite reaction. The nervous impulses of opposite signs
reaching different flanks of the inotile organ is thus of
importance in the co-ordination of the resulting movement.

LXIII.— THE ELECTEIC EESPONSE OF
MIMOSA PUDICA.

By Sie J. C. BosE,

Assisted by
SuRENDRA Chandra Das, M.A.

All plants and their various organs have been shown to
exhibit an electric response under stimulation, the stimu-
lated tissue being rendered galvanometrically negative. In
Mi))i()fi(i we have a conspicuous response by mechanical
movement. The effect of changes of environment on the
plant may thus be detected by induced variations in the
mechanical response, which may be automatically recorded
by the Kesonant and Oscillating Eecorders. A study of the
electric response of Mimosa is of interest, because it enables
us to find out whether the two independent methods of
record correctly indicate the fundamental physiological
change which is induced in the organism by external
variations.

The pulvinus of Mimosa is a dorsi-ventral organ, the
excitability of the lower half being very much greater than
that of the upper. Hence an identical stimulus induces
a relatively greater excitatory reaction at the lower side.
It has been shown, that the induced change of galvanometric
negativity depends on the intensity of excitation ; hence, on
making electric connections with the upper and lower sides
of the pulvinus, a diffuse stimulation w^ould be expected to
exhibit a resulting galvanometric negativity of the lower

751

752 LIFE MOVEMENTS IN PLANTS

half of the organ. Having explained the general principle,
we have next to devise practical methods for obtaining the
electric response.

THE EXPERIMENTAL METHOD.

The electric connections with the upper and lower
halves are made with gold or platinum wires. In order to
secure good contact, two separate pieces of cork are held

P^ig. Ii8() Alc'llioil fur obuiiiiiriji- fleet ric ri'spi/ii.v,^- of tlio pulviiiiis of
Mimosa. Stimulus of electric shock obtained from the secoiKlary S, of an
induction coils. Tlu; chokinj^ coil C, prevents leakaufo of shock-current
into the galvanometer circuit. The upper illustration shows the electric
connections with the two halves of tlic pulviiiua.

together by four short lengths of elastic. The connecting
gold wires, above and below, liave their torminni (MuIs
flattened, so as not to cause any wound to the pnlvimis; a
drop of kaolin paste in normal saline makes a perfect
electric contact ; a small (piantity of glycerin is added to the
sjiline solution to prevent rapid drying of the kaolin paste.
The slightly stretched elastic keeps the pressure of contact
constant. The small pieces of cork are light and,
therefore, do not exert any appreciable weight on

ELFXTRTC RESPONSE OF MBfOSA PUDICA 753"

the leaf (Fig. '29,6). Tlie complicated metlicxi of
electrolytic contact by means of iion-polarisable electrodes
is not only unnecessary, but often harmful ; for unless
great precautions are taken the zinc sulphate solution may
leak and come in contact with the plant abolishing its
excitability. The amalgamated zinc rods, moreover, are
not absolutely iso-electric. These drawbacks are not
present in the platinum or gold contacts, for pure specimens
of these metals could be made iso-electric after annealing.
The direct method of contact reduces the resistance to a
minimum. The object of non-polarisable contacts is to
diminish the counter-electromotive force due to the passage
of the ('urrent. This comiter E. M. F. depends on the
strength of the current ; since the responsive current of the
plant is very feeble, it does not in practice give rise to any
appreciable polarisation.

The problem which offered the greatest difficultx in this
investigation is in securing uniform stimulations in succes-
sion, or in increasing the stimulus in a perfectly graduated
manner. The only means by which this can be secured is
by tetanising electric shocks of definite intensity and
duration. The intensity may be continuously increased by
pushing the secondary coil nearer the primary. The
duration of application may be kept the same in successive
experiments by completing the primary circuit of the coil
(provided with the usual vibrating hannner* for a definite
length of time by means of a metronome. The two termi-
nals of the secondary coil are applied to the petiole at certain
distance from the pulvimis, and the electric responses to
successive transmitted excitations are recorded on a umving
photographic plate by the excursion of the spot of light
reflected from the galvanometer.

The oscillatory induction shock introduces, however, a
comphcation by the Ir^akage of the shock-current into the-

754 LJFK ]\I()VEMF,NTS IN PLANTS

galvanometer. This difficully has, however, been com-
pletelv removed by tlie interposition of a maj:jnetic choking
coil, which prevents the rapidly alternating current to enter
the galvanometer circuit.

All iin|)ortant condition for obtaining the normal electric
response is the maintenance ot the plant in a favourable
tonic conchtion. It is thus necessary to expose the })]ant to
diffuse light of the sky. As tlie ])]iotographic records
require a dark I'ooni, the leading \\'ires tVoni the j)lant are
carried to the galvanonietei- in the photograi)hic room.

Electric response to Transmitted Excitation. — Klectric

stinmlus of uniform intensity is applied at intervals of 10

minutes or so, and the resulting response
Expoiiiuent 'Jit'.i , , „,, , , . , ,

recorded. Lhe ])liot()g)'apnic plate was

moving at a slow i-ate, hence the record of response and

lecoveiN are almost superposed; it will be noted that the

auiphtude of successive responses under uniform stimulus is

the same (Fig. "287). The res|)onse is by galvanoinetric

negativity of the more excitable lower half of the pulvinus.

This eoiiesponds with the responsive fall of the leaf by the

relatively greater contraction of the lower half.

EFFECT OF EXCESSIVE ABSORPTION OF WATER P.Y THE
PULVINUS.

A muscle nmnersed in distilled water loses its ])ower of
contraction. Application of water to the ])ulvinus also
renders it irresponsive. This is seen on rainy days, when
the sensibility of the pulvimis is found to be practically
abolished. A more definite result was obtained in the
following experiments. After obtaining the normal
mechanical response, a droj) of water was a])plied to the
l-ulvimis, an.d the I'esulting" absorption of water in excess
caused a com|)]ete abolition of motile excitability. In con-
nection with this it sluMdd be i-eniembeied that excitatory

ELECTRIC RESPONSE OF JIIMOSA PUDICA 1 '>5

contraction is brought about by the expulsion of the sap
from the puivinus ; its over-inflated condition may,
therefore, oppose the excitatory contraction with resulting
aboHtion of the mechanical response.

A question now arises, whether this absence of mecha-
nical response is due to the abolition of irritability, or merely
to physical restraint imposed by the over-turgid tissue. This
subject may be experimentally tested by means of electric
response, which is independent of mechanical movement.

FIG. 287 FIG. 288

Fig. 287 Uniform response of galvanometric negativity under uniform
stimulations of moderate intensity {Mimosa).

Fig. 288 Positive electric response in Mimosa, under feeble stimulus.

For, the leaf of Mimosa may be held fixed without interfer-
ing with its electric response. This fact explains th'^
occurrence of electric response in ordinary plants, in which
there is no conspicuous movement in response to stimulus.

The puivinus of Mitnosa was made mechanically
irresponsive by application of water. In this condition,

mechanical or electrical stimulation did not
Esperiment .SUO 1 j- 11 ^ ^i 1 £ \

cause the normal tall or the lear. An

electric record was next obtained, and it was found that the

75(1 LIFE MOVEMENTS IN PLANTS

mechaiiKally insensitive leaf gave the normal electric
response of galvanometeric negativity, proving that the tissue
was still irritable though unable to manifest it outwardly
by mechanical movement.

EFFECT OF FEEBLE STIMULUS.

The transmitted excitation due to sliuiulus of moderate

intensity causes, as we have seen, a response of galvano-

metric negativity of ih(> more excitable
E.\|)ei'iment HHl i .,■ i. , " i ■ mi

lower Jiali ot the pulvmus. ihc mtensity

of stimidus in the following experiments is reduced by
removing the secondary coil away from th<^ })rimary.
Feeble stimulus is now found to induce a response which is
of opposite siijn to that of the normal, namely by galvano-
}urtric positivity, indieatii'c of expansion instead of normal
contrdctid}! (Fig. '288'. The opposite responses observed
tinder feeble and stri)ng stinuilus appears to be of general
occurrence. We have already found that while strong
stimulus induces a contraction and retardation of growth, a
feeble stimidus induces the opposite effect of expansion and
acceleration, (see Fig. '278>. Similar effects are also found
in geotropic response where the upper side, subjected to
moderate stimulus, exhibits contraction, and the lower
■side, under enfeebled stimulation, shows expansion (p. 629).
If the stimulus be gradually increased, the response
changes from positive to normal negative, sometimes
through a diphasic res|X)nse, positive followed by negative.
The particular intensity above which th<', response is trans-
formed from positive to negative, may be termed the
critical intensity. This critical value is found to depend on
the tonic condition of the tissue. Tn a highly excitable
specimen, the critical point is low, and the normal negative
response takes place even under moderately feeble stimulus.
The critical point is. however, raised when the tissue falls

ELECTRIC RESPONSE OF MIMOSA PUDICA l')7

into a 8ub-tonic condition ; the positive response under

feeble stimulus may tlien be obtained without difficulty.

Positive response of Sub-tonic tissues.— The plant is

kept in diffuse light, and the {)arlicular intensity of stimulus

which invariably gives negative response is
Experiment 302 . , ■ ^ i . , i t

determined. A cover is next placed over

the plant so as to maintain it in darkness for about an hour,
thus inducing a condition of sub-tonicity. Application of
the stimulus wliich previously induced a negative response
is now found to bring about a positive response. The plant
is next exposed to light, for improving its tonic condition.
Ttie response is now found once more to be a normal
negative.

We found the occurrence of a similar positive mecha-
nical response in Mimosa in a sub-tonic condition (Vol. I,
Experiment 50); the characteristic effects of stimulus on
growth are also similar, that is to say, while in the normal
condition of the plant stimulus causes a retardation of
growth, in a sub-tonic condition, it gives rise to an enhance-
ment of growth (Experiment 88).

CONDUCTING PATH FASHIONED BY STIMULUS.

It has been shown that the phloem of the fibro-vascular

bundle functions as the nerve by which the excitation is

transmitted. Tn voung leaves the phloem

Experiment 303 . ^ i ^ -^ e

IS anatomically ])resent, but its power ot

physiological conduction has not yet been developed. It is
of extreme interest to follow the manner in which the con-
ducting power in young tissues is functionally developed by
the action of stimulus. We take a young leaf of Mimosa,
and apply stimulus of moderate intensity to the petiole at
«ome distance from the responding pulvinus, the distance of
the secondary coil from the primary being noted at the same
time. The tissue is found to be non-conducting to the
stimulus, as indicated bv the absence of normal response of

758 LIFE MOVEMENTS IN PLANTS

galvanometric negativity. The stimulus is next increased
by bringing the secondary nearer the primary coil; the
block to conduction is now found to be suddenly removed,
and the conducted excitation ,i;ives rise to the normal
negative response. We next remove the secondary away
from the primary to the first ineffective position. But the
formerly ineffective stimulus is now found to be effectively
transmitted, the response being the normal negative.
Stinudus is thus found to fashion its own conductiii';" Dath.

SUMMARY.

The normal electric response of the pulvinus of Mimosa
to transmitted excitation is by an induced galvanometric
negativity of the more excitable lower half of the pulvinus.

Excessive absorption of water abolishes the mechanical
response of the pulvinus. The electric response is, however,,
found to persist, proving that the tissue is still irritable
though unable to manifest it outwardly by mechanical
movement.

Feeble stimulus gives rise to a response wliich is of
opposite sign to that of strong stimulus.

The critical intensity of stimulus for normal negative
response depends on the tonic condition ; it is low when the
tissue is highly excitable, and liigh when the tonic condition
falls below par.

In young plants, the nervous elements are present
though not functionally developed for conduction of excita-
tion. In such a condition, stimulus is found to fashion itn
own conducting path.

LXIY.— SIMULTANEOUS DETEEMINATION OF

VELOCITY OF EXCITATION BY

MECHANICAL AND ELECTRIC METHODS.

By Sir J. C. Bose,

Assisted by

Basiswar Sen, B.Sc.

It has been shown in the last chapter that the more
excitable lower half of the pulvinus exhibits, under trans-
mitted excitation, a galvanometric negativity in reference to
the upper side. This differential effect is parallel to the
greater contraction of the lower side by which the leaf
undergoes the normal fall.

The excitatory impulse generated at a distance has been
shown to be of nervous character. A certain time elapses
between the application of stimulus and the response given
by the pulvinus. The period of transmission, and our know-
ledge of the intervening distance between the point of
application of stimulus and the responding pulvinus, enable
us to determine the velocity of transmission of excitation.
Allowance must be made for the physiological inertia of the
pulvinus, the latent period of which has been found to be
about a tenth of a second.

DETERMINATION OF VELOCITY BY THE MECHANICAL TIIETHOD.

The determination of the velocity of transmission by
mechanical response is made by the Eesonant Recorder,
fully described elsewhere.* The writer AV, made of fine

* Irritability of Plants, p. 140.

L

760 LIFE MOVEMENTS IN PLANTS

steel wire with a bent tip, is at right angles to the lever
and is maintained hy electromagnetic means in a state of
to-and-fro vibration, say ten times in a second. The writing
index is previously tuned so as to vibrate at this rate. The
steel wire is supported at the centre of the pole of an electro-

Fi(i. 289 Resonant Rec-order for (loti-niiination of velocity of trans-
mission of excitation. The falling plate during descent made electric
contact of R with R' for indnction shock by the secondary coil S.

magnet which is periodically excited by a current inter-
rupted by a reed ; when the reed is exactly tuned to vibrate
ten times in a second, the writer is thrown into sympathetic
vibration. The successive dots of records thus indicate
intervals of a tenth of a second (Fig. 289). Employing

SIMULTANEOUS DETERMINATION OF VELOCITY 761

this method, the velocity of transmission in the petiole of
Mimosa was found to be about 30 mm. per second in an
excitable specimen of the plant. The velocity depends on
the physiological condition; under depressed condition in
winter, the velocity is found lowered to about 4 mm. per
second.

We have hitherto employed the Eesonant Recorder for
the mechanical, and the galvanometer, for the electric
response of Mimosa. The problem that now confronts us
is the determination of the mutual relation of these two
different modes of response, whether they indicate the same
fundamental physiological reaction which underlies excita-
tion. For this, it is necessary to devise some means of
obtaining simultaneous records of the two responses given by
an identical specimen. We may carry out this idea further
and determine the velocity by the two independent methods
of mechanical, and electrical responses. The identity of the
two results thus obtained will afford conclusive proof that
the mechanical and electric responses are but different
expressions of the excitatory change induced by stimulus.
In connection with this it should be borne in mind that the
inertia of the mechanical and the electric recorders are not the
same ; but the difference may be so slight as to be negligible
in practice. The electric response is, in general, obtained
by a galvanometer, with its high sensitivity, a moderately
delicate apparatus giving a deflection of 1 mm. for a current
of 10 10 ampere. This great sensitiveness is, to a certain
extent, nullified by the high electrical resistance of the plant,
on account of which the current in the circuit is greatly
diminished. There is another drawback in the use of the
galvanometer in certain experiments on the absolute deter-
mination of the electromotive variation induced by stimulus,
for it also gives rise to a diminution of electrical
resistance of the tissue. The increased deflection mav

762 LIFE ^MOVEMENTS IN PLANTS

therefore, be not solely due to an increase in the induced
electromotive force. For certain special investigation it is,
therefore, of advantage to employ an electrometer, instead of
a galvanometer. In the electrometer, the circuit is open,
and its indications are, therefore, independent of resistance.

THE ELECTROMETRIC ^METHOD.

It (loos not appear that the Quadrant Electrometer has
been used for physiological work. The prevailing impres-
sion is (1) that it is not sufficiently sensitive, (2) that it is
difficult to keep the needle charged for days to the same
potential so that its sensitiveness and zero position remain
constant, and finally, (3) there is a misgiving that its deflec-
tions are affected by external disturbances.

As regards the sensitiveness, it has been possii)le to
raise it sufficiently high by employing a long suspension of
fine quartz thread rendered conducting by the usual method.
The sensitiveness may, with care, be thus raised so as to
give a deflection of 1 mm. for a thousandth of a volt.

The dry cells are unsatisfactory for charging the needle;
Cu-Zn elements in water are, on the other hand, fully
satisfactory. The cells are made by scooping out a series
of large sized holes in a thick block of solid paraffin. A
sufficient number of Zn-Cu elements are placed in series
so as to give a terminal difference of potential of 110 volts.
The zero position of the reflected spot of light is then found
to remain constant for many days in succession.

The insulated pair of quadrants is suitably connected
with the lower half of the pulvinus. The pot containing
the plant is connected with the second pair of quadrants,
which is earthed.

SIMULTANEOUS MECHANICAL AND ELECTRIC RECORDS.

For obtaining simultaneous records, the recording
glass plate for mechanical, and the photographic plate for

SIMULTANEOUS DETER1\[INATI0N OF VELOCITY 7tiS

the electric record, are allowed to fall at the same rate by
means of a clockwork. The spot of light reflected from the
mirror of the electrometer falls on the photographic plate
and records the electric response. We have next to employ
some device for obtaining the time-relations of the two
curves.

As regards the mechanical record given by the Eesonant
Recorder, the successive dots re]n-esent intervals of tenths

Fig. 2fO Simultaneous records for velocity of transmission. The
upper is the mechanical, and the lower, the electric record. The time- ^
interval for initiation of response is found in both cases to be 0.7 second.

ot a second. Hence the curve of response is its own chrono-
gram. For obtaining the time-relations of the electric
curve, the reed which actuates the Eesonant Recorder, is
interposed in the path of light reflected from the mirror of
the electrometer. The reed has a piece of ahmiinium,

764 LIFE MOVEMENTS IN PLANTS

which interrupts the lif^lit ten times in a second. The

photo orajihic record thus consists of Hnes of lioht alternating

with darkness ; the successive dots in the mechanical record

thus correspond Avith these lines of lifiht.

After makinj^- the arrangements described above

the two plates are allowed to fall at the same rate. Stimulus

of electric shock was now ai)])lied to
Experiment 3(14 , . , _ „ ^ ^

the petiole at a distance of 20 mm. from the
pulvinus. There was no immediate response either
mechanical or electrical ; but after an interval of 7 dots, the
leaf began to fall, causing a mechanical record upwards.
The interval between the application of stimulus and the
initiation of response is thus 0.7 seconds. ^Making an
allowance of 0.1 second for the latent pei'iod of the pulvimis,
the time required for transmission of excitation through 20
mm. is thus 0.6 seconds. The velocity is thus 33 mm. per
second.

The electric record gave an identical result ; the
response was initiated at the 7th strip of light, that is to
say at the same time as the mechanical response (Fig. 200).

It is thus seen that the transmitted excitation, which
induces a fall of the leaf by relatively greater contraction of
the more excitable half of the ])ulvinus, also induces a
simultaneous electromotive cliange of galvanometric
negativity of the lower half of the organ. The velocity of
transmission obtained by the two methods are thus prac-
ticallv the same.

su:mmary.

A Quadrant l\lectr()meter may be om|iloyed for obtain-
ing electric response of plants. The advantage of this
method lies in the fact that the observed response is due to

SIMULTANEOUS DETERMINATION OF VELOCITY 765

induced electromotive variation, unaffected by the resist-
ance of the circuit.

A simultaneous determination of the mechanical and
electric responses is made by the employment of the
Eesonant and Electric Eecorders connected with the same
leaf. The records thus obtained show, that the mechanical
response of the leaf has an electric concomitant in a
negative electromotive variation.

LXV.— THE MULTIPLE EE8P0NSE IN MIMOSA.

By Sir J. C. Bose,

Assisted by
SuRENDRA Chandra Das, m.a.

The character of different modes of response — by electric
variation, by the movement of the leaf, and by variation of
the rate of growth — has been shown to be determined in a
definite way by the intensity of stimulus. Under sub-
minimal stimulus the response is positive, — a positive electric
variation, an expansion and erectile movement of the leaf,
and an acceleration of the rate of growth. Stimulus of
moderate intensity induces, on the other hand, a negative
electric variation, a contraction and fall of the leaf, and a
retardation of the rate of growth. The critical intensity of
stimulus for transformation of the positive into negative
response is modified by the tonic condition of the tissue ;
under sub-tonic condition the critical point is high, so that
even a moderate intensity of stimulus induces a positive
response. The tonicity of the tissue is, however, improved
by the action of the stimulus, and in consequence of previous
stimulation the positive response is transformed into the
normal negative.

Having observed the effects of sub-minimal and of
moderate stimulus, we shall next study the effect of intense
stimulation. For this purpose we may take a leaf of
Biopltytum or of Averrhoa in which there are numerous
pairs of sensitive leaflets. We attach one of these leaflets

766

THK MULTIl'LE MliSPONSH IX MIMUSA 7()7

to an Oscillating Eecorder, and observe the response induced
by stimulus applied at the petiole at some distance from
the leaflet. The effects of feeble and moderate stimulus
are similar to what we have already observed, namely, a
positive and negative response respectively. We next
apply a stronger stiiiinhis and find that the response is not
single but multiple (see Fig. 295). For obtaining records
of these multiple responses it is necessary to prevent the
complete closure of the leaflets by w^hich further response
is rendered impossible. This is secured bv applying a light
counterpoise in the second arm of the lever, which, exerting
a tension, opposes the complete closure of the leaflet.

These multiple responses are found to occur under any
form of strong stimulation, the stimulus being as diverse
as induction shocks, strong light, thermal shock, and
chemical excitation.

ilULTIPLE ELECTRIC EESPONSE IN MIMOSA.

Having seen that a recurrent series of responses occur
under a single strong stimulus in multiply responding plants
like Biophytiim and Averrlioa, we shall next try to find out
whether similar responses may be obtained from Mimosa
which, generally speaking, gives but a single response to a
single stimulus. For this we shall first employ the electric
method of investigation.

Electric connections are made in the usual manner
with the upper and lower halves of the pulvinus, and the
galvanometric response recorded on the
photographic plate. The petiole, at a dis-'
tance of 3 cm. from the pulvinus, was strongly stimulated
by application of a hot wire. This gave rise to a very large
response of galvanometric negativity, so large as to take the
spot of light away from the plate ; after the spot of light
came back to the plate during recovery, there occurred

768 LIFK MOVEMENTS IN PI.ANTS

a second response followed by a recurrent series of other
responses. In order to keep the spot of lifiht within the
plate, a less excitable specimen was next employed, and
strong- stimulus applied as before. This is seen to have
^iven rise to a series of six recurrent responses. (Fig. 291).

MUI.TIPLK :\lKt'TIANICAL KESrONSR.

Though the multiple electric response may be obtained
with Mi)))<)sa without much difticultv, vet I failed for a long

FIG. 2vl

FIG. ^92

Fi.s,'. 291 Multiple elertric iv!S])onsi>s under a siiif^'le i^troii^' siiiiiulus

(Mimofa).
Fiir. 2^*2 .Multi))lc iiiccli!niic;il resjioii.'je in Mimasn under stronj; stimulus.

time to obtain corresponding mechanical responses which
were multiple. This failure I have since been able to trace to
the following; (1) the heavy leaf is unable to follow the
relatively ()uick ivcurrent responses, ("2) strong stinndus
gives rise to a Tall wliieli is maximum and in this state of
complete fall, further resj)onses camiot be detected, (3) the
subsequent res})on.ses are rcdatively small compared to the

THE MULTIPLE RESPONSE IN MIMOSA 769

amplitude of the first response ; hence a higher magnifica-
tion is necessary. A high magnification, however, makes
the first record go completely out of the plate. The practical
difficulties in obtaining multiple mechanical responses are
thus seen to be very numerous. They have been to a
certain extent removed by the following devices.

The weight of the leaf is reduced to a minimum by
cutting off the sub-petioles, leaving a short length of the
petiole for attachment to the recording lever. The shock of
operation makes the plant temporarily insensitive; but after
a period of rest of one or two hours the excitability is found
to be restored.

For preventing the complete fall of the leaf a suitable
counterpoise is placed on the opposite arm of the lever to
exert a tension. Finally a moderate magnification is
employed so as to keep the record within the smoked glass
plate.

After taking these precautions record was taken of the
effect of strong stimulus caused by application of a heated
wire to the stem below the leaf. This gave
rise first, to a large response of the fall of
the leaf, followed by a partial recovery ; there then occurred
a second response (Fig. 292) ; in other cases there were
three recurrent responses of the Mimosa leaf under a single
strong stimulus.

A continuity is thus established between the multiple
responding plants like Biophytum and ordinarily responding
plant like. Mimosa. Feeble stimulus induces in these
plants a positive response and a moderate stimulus causes
a single negative response. Strong stimulus, however,
gives rise in all these cases, to a multiple series of responses.
"We shall, in the next chapter, find that this continuity
is extended to the autonomous response which is c?aused by
some internal stimulation.

770 LIFE MOVEMENTS IN PLANTS

SUMMARY.

The response of plants exhibits three different character-
istics, depending on the intensity of stiinuhis apphed.
Under suh-niinimal stiniukis, both the mechanical and the
electric responses are single and positive ; under moderate
stimulus, it is negative. But under strong intensity, a
single stimulus gives rise to a recurrent series of responses.
This is true of all plants, ordinary and sensitive.

Multiple response under strong stimulus is typically
exemplified by the leaflets of BiopJiytnm and Avcrrhoa. In
these, strong stimulus of all kinds, — electric, thermal,
pliotic, and chemical — gives rise to nuiltiple responses.

In the ordinarily responding plant like Mimosa, which
gives a single response under a single moderate stimulus,
multiple electric and mechanical responses occur under the
action of a ningle strong stimulus. A contiruiity of response
is thus estabhshed in all types of plants.

LXVI.— THE EFFECT OF CAEBON DIOXIDE

ON THE MECHANICAL AND ELECTRIC

PULSATIONS OF DESM ODIUM GYRANS.

By Sir J. C. Bosb,

Assisted by
Basiswar Sen, B.Sc.

We found in a previous chapter that the autonomous
activity of growth is arrested by the action of carbonic acid,
and that a renewal of the activity takes place on substitution
of fresh air. The pulsating movements of the lateral
leaflets of Desmodiiun gyrans is a striking example of
autonomous or internal activity, and we shall in the present
chapter study the effect of carbon dioxide on the ' spontane-
ous ' movements of the leaflet.

It may be stated here that strictly speaking, there is no
such thing as spontaneous movement. The energy which
expresses itself in pulsatory movements is derived by the
plant either directly from the immediate external sources,
or from excess of such energy already accumulated and held
latent in the tissue. When the storage is exhausted, as
when the plant is kept in a dark room, the rhythmic pulsa-
tions are found to come to a stop. The pulsation of the
leaflet can, however, be renewed by the application of fresh
stimulus, the persistence of the pulsatory movements being
dependent on the quantity of incident stimulus. The
responsive characteristic of the Desmodiiun leaflet in a
state of standstill is similar to that of the leaflet of

771

7 72 LIKK MOVKMKNTS IN PLANTS

Biopltytinn. It ^ives rise to a single response to a single
moderate stimulus, and to multiple responses to a strong
stimulus. A continuity is thus seen to exist between the
multiple responding leaflet of Biophytum, and the auto-
matically pulsating leaflet of Dcsmodin))i.

EFFECT OF CARBONIC ACID GAS ON MECHANICAL PULSATION.

A cut stem with the petiole bearing the lateral leaflets

is suitably mounted in a test-tube filled with water ; the

shock of operation passes away in the course

of about an hour when the pulsations

become renewed. One of the leaflets is now attached to an

Fiu'. '2\^'.i KtY(M-t <if C()_, oil nutoncmious iiicclKiuic.-i 1 iiulsaliini of
iJeamixlium gyrans.

Note arrest under C().^ ;i|i|ilic(l :ii arrow and Mii>sfi|iu'iit revival on
iiit roduct ion of fresli air.

Oscillating Kecorder for obtaining tracings of its normal
pulsations. A stream of carbonic acid gas is next passed
into the plant chamber ; this is seen to induce a complete
arrest of the pulsations (Fig. 293). Fresh air is next
substituted in the plant-chamber; this renews the arrested
pulsation. In fact, the pulsations are now found to be
more vigorous than at the beginning. It seems as if the

THE EFFECT OF CARBONIC ACID GAS 773

energy of pulsation, hitlun-to held in restraint, now found
an enhanced expression.

EFFECT OF CARBONIC ACID GAS ON ELECTRIC PULSATIONS.

Each pulsation of the Desmodium leaflet consists of a
rapid down-movement followed by a slow up-movement.
The maximum rate of down-movement is about 1.5 mm.
per second, while the corresponding rate of up-movement is
only 0.5 mm. per second. It would appear that the down-
and up-movements are brought rbout principally by the
alternate contractions of the lower and upper sides of the
pulvinule. Thus the lower half contracts rapidly, followed
by a recovery ; during this recovery the upper half contracts.
The pulsations are thus due to alternate variations of turgor
on the opposite sides of the organ. A parallel instance is
found in circumnutation of certain growing organs, in which
alternations of growth at the two opposite sides of the organ
give rise to lateral oscillations.

I have succeeded in obtaining records of the electric
pulsations of the Desmodium leaflets in the following
manner. We make two electric contacts,
one with the more effective lower half of the
pulvinule, and the other, with a distant indifferent point.
The electric pulsations, to be presently described, take place
independently of the mechanical movement, hence the leaflet
may be held fixed without interfering with the electric
pulsations. During the phase of contraction of the lower
half, that half becomes galvanometrically negative, and we
obtain a large electric pulsation. This pulsation is often
attended by a small subsidiary pulsation, probably due to
comparatively feeble excitation of the upper half of the
pulvinule.

The records given in Figure 294, exhibit uniform
electric pulsations. On introduction of carbonic acid gas

7 74 LIFE MOVEMENTS JN FEANTS

into tlie planl-chaiiihcr, the pulsations det'liiied rai)i(lly and
ultimately came to a stop, as in the case of the mechanical
pulsation. Carhonic arid pas was next romoxcd hv l)l()winfi

Fig. 294 Effect of C()2 <>n electric piilsatioti.s of iJcsinodium gyrans.
Note the two nornml electric ])ul-ation and suhsei|ii(Mit arre.st under COj.
Last record shows enlianccd pulsiitioii on I'ciiewal of frcsli air.

in fresh air, when the electric pulsations were renew^ed even
with additional vigour.

SUMMARY.

There i;, a continuity of response in multiple responding
pbint lil\-(" Biopliyiniii and the automatically responding

THE EFFECT OF CARBONIC ACID GAS 775

plant lik^ Dcsmodium. On depletion of absorbed energy,
Desmodium leaflet comes to a state of standstill. It gives
then, like Biophytum leaflet, a single response to a single
moderate stimulus, and multiple responses to a stron^;
stimulus.

The mechanical pulsation of Desmodium leaflet is
arrested by carbonic acid gas. Introduction of fresh air
renews the pulsations.

The leaflet of Desmodium exhibits electric pulsations in
response to internal activity which maintains the mechani-
cal pulsation. The electric pulsation is, however,
independent; of mechanical movement ; it persists even after
the leaflet is fixed so as to prevent its mechanical pulsation.

The effect of carbonic acid gas on electric pulsation is
similar to that on mechanical pulsation. It arrests the
pulsations during the continued action of the gas. Substi-
tution of fresh air is followed by the renewal of electric
pulsation.

M

LXVII.— THE TRANSMISSION OF DEATH
EXCITATION.

By Sir J. C. Bose,

Assisted by
Basiswar Sen, B.Sc.

Experiments have been described in a previous chapter
which showed that plants exhibit a death-spasm at a
critical temperature, which is at or about 60°C. Considera-
tions were adduced to prove that this was not a phenomenon
of coagulation, but an excitatory reaction which occurs at
the moment of death.

This will find an independent support, if we succeed in
demonstrating the occurrence of an excitatory impulse at a
point distant from the indicator. Thus, on the exposure of
a portion of the stem of Mimosa to rising temperature, it
may be expected that an intense excitatory impulse would
be initiated at the critical temperature and transmitted
to the distant leaves causing their fall. The faot
of this transmitted excitation would undoubtedly afford
crucial proof of the excitatory reaction at death. The
experiments described below were carried out not with
Mimosa alone, but with other sensitive plants such as
Biophytum and Averriwa.

EXPERIMENTAL ARRANGEMENT.

It may be stated that the leaves and leaflets of cut
specimens of Mimosa, of Averrhoa and of Biophytum can

770

THE TRANSMISSION OF DEATH EXCITATION 777

be made to exhibit all the irritable reactions of the intact
plant. After section of the stem or the petiole the shock of
operation causes a temporary abolition of excitability ; but
after a period of rest, the sensibility is found restored. The
stem or the petiole is then so supported that its cut end is
immersed in a water-bath to a depth of 2 cm. The bath
consists of a thin-walled water vessel with arrangements for
electric heating by means of a coil of wire. It is easy to
regulate the rise of temperature, to a standard rate of 1°C.
per minute, by means of the rheostat included in the circuit.

CRITICAL TEMPERATURE FOR TRANSMISSION OF
DEATH-EXCITATION IN MIMOSA.

Transmitted excitation at death-point in cut speci-
mens.— In carrying out the experiment in the manner

described above, it was found that the
Experiment 309 -, . „ . , -,111

steady rise 01 temperature m the bath

did not at first produce any effect on the distant

leaves ; but on the attainment of a certain critical

temperature, an intense excitatory impulse was generated

in the immersed portion of the stem, which, travelling

upwards, caused an abrupt fall of the leaves in a serial

succession. This could only be due to the transmitted effect

of excitation occurring at the local death of the immersed

portion of the stem; for the leaves re-erected themselves,

and recovered their normal excitability after a period of

about 20 minutes. That the excitation was due to the death

of the immersed portion was proved by repeating the

experiment. This time there was total absence of

any responsive fall of the leaves, showing that

the immersed portion had permanently lost its power

of initiating any further excitatory impulse on account

of its death. But the result was quite different,

when the experiment was repeated for the third time after

778 LIFE MOVEMENTS IN PLANTS

lowering the same stem through further 2 cm. in the heating
bath. A new excitatory impulse was found to be initiated
at the critical temperature by the death of the freshly
immersed portion of the stem, the impulse causing the
usual fall of the leaves.

The experiment, just described, demonstrates conclu
sively the occurrence of an intense excitatory reaction in the
tissue at the moment of its death.

It was shown in a previous experiment that the death-
point of the pulvinus is at or near 60°C. An interesting
question now arises : Is the death-point of an ordinary non-
motile tissue of the stem the same as that of the contractile
tissue of the pulvinus, or is it dilferent? In carrying out
experiments with fresh j)reparations of cut specimens, the
temperatures at which transmitted death-excitations
occurred w^ere found in four typical cases to be at 64°C.,
64PG., 65°C., and 65°C. respectively. The distance of the
nearest leaf was, in all cases, 20 mm. from the iimnersed
portion of the stem. A slight error is introduced in the
determination of the death-point from the fall of the leaf,
since there is a short time-interval between the initiation of
exH;iitation in the immersed stem and its detection by the
leaf at a distance of 20 mm. Taking the average value of
the velocity of transmission in the stem under normal con-
ditions to be about 5 mm. per second, the fall should occur
4 seconds after the initiation of the excitation. The rate of
rise of temperature in the bath is 1°C. per 60 seconds;
hence the error introduced in the determination of the death-
point by the adoption of the indirect method of excitation
would amount to a fraction of a degree, which may be
regarded as quite negligible.

The velocity of transmission in intact specimens has
been taken as of the order of 5 mm. per second. This may
not, however, be the actual value in a cut specimen ; for I

THE TRANSMISSION OF DEATH EXCITATION 779

find that the injury caused by the operation causes a
depression in the conducting power. Hence in a cut speci-
men there may be induced a great delay in the passage of
the excitatory impulse, on account of which an error of
several degrees may be introduced in the determination of
the death-point.

The conducting power in an isolated preparation is, in
general, more or less completely restored after a prolonged
period of rest. In the next batch of preparations, the
experimental determination of the death point was under-
taken six hours after isolation from the parent plant ; the
different values of the death-point were now found to be :
6-20C., 620C., 630C., and 63°C. respectively.

Experiynent with intact specimens. — From the fact
that the disappearance of the effect of injury tended to bring
the death-point nearer the normal 60°C., I was next led to
experiment with intact plants. For this, I took a batch of
young seedlings of Mimosa and carefully removed them
from the ground without injuring the roots. The lower
part of the plant was placed in the bath in the usual manner
and the death-points observed in four typical cases were :
60OC., 60°C., 59.60C., and 60OC. respectively. It will
thus be seen that an excitatory impulse is generated at the
critical death-temperature, and that the death-point in an
ordinary tissue is the same as that in sensitive pulvinated
organs.

CRITICAL POINT FOR TRANSMITTED DEATH-EXCITATION IN
AVERRHOA.

Similar experiments were next carried out with cut

petioles of Averrlioa, and one of the sensitive leaflets was

chosen for detection of transmitted excita-

Experiment 310 ^.^^ ^^^^ ^^^ attached to a delicate

Oscillating Recorder for obtaining record of transmitted

780 LTFK MOVEMENTS IN PLANTS

excitation. As regards the character of this excitation in
Averrhoa and Biophytum, I have shown elsewhere that
under intense stimulation, the response instead of being^
single becomes multiple. The death-excitation, if intense,
is thus expected to give rise to a multiple series of responses.
The cut end of the long petiole was gradually raised in
temperature at the standard rate of one degree per minute.
The indicating leaflet was at a distance of 50 mm. from
the cut end. The velocity of transmission of excitation is
relatively slow, less than 1 mm. per second ; hence by the
time the excitation reaches the distant leaflet the observed

Fi<f. 29.5 Transmitted {leath-e.xcitatioii <;iviii^ ri.se to multiple res-
ponse in Averrhoa. -. this occurred at 62**C.

temperature in the bath would have risen one or two degrees
higher. Figure 295 shows that a death-excitation was
generated at the critical temperature, which had given rise
to a multiple series of responses. The temperature at which
this occurred was 62°C., which for reasons explained above
was one or two degrees above the true death-point. The
bath was allowed to cool down and the temperature was
raised once more; but there was no transmitted excitation
since the immersed portion had been previously killed. The

THE TRANSMISSION OF DEATH EXCITATION 781

petiole was next lowered by 2 cm. thus bringing a fresb
unkilled portion in operation, and the transmitted death-
excitation was found to occur once more as at the beginning.
This proves conclusively that the transmitted excitation is
generated at the critical temperature at the moment of
death of the living tissue. The fact that heat caused only
local death was independently proved by the effect of direct
stimulation of the leaflet after the multiple response of the
transmitted excitation had come to a stop. Stimulation of
the indicating leaflet gave rise to the normal response. The
effects described above were also found in Bioplujtum.

EXCITATORY IMPULSE AT DEATH BY POISON.

The determining cause of the excitatory impulse lies
not in the manner of death but in death itself. The same
excitation may be initiated in the complete absence of
scalding or of coagulation. A quick method of bringing
about death is in the administration of poison. We might
thus be successful in discovering the transmitted excitation
at the death of the tissue under poison.

Transmitted excitation in Mimosa. — For this investi-
gation I first took intcict seedlings of Mimosa ; the roots and
the stem were immersed in a beaker of
xpei linen . ^r^ter, the distance of the nearest motile
leaf being 2 cm. above the point of immersion.
Another beaker was kept' ready containing poison
of a definite strength, either 1 per cent, or 5 per cent,
solution. This was applied by substituting the beaker con-
taining the poison for the beaker of water. It is obvious
that the quickness with which a tissue is killed will depend
on the strength of the poison : the transmitted death-
excitation, if any, will be exhibited earlier under a strong
than under a feeble poison The effective intensity of a
poison will depend not only on the strength, but also on
its relative virulence.

782 LIFE MOVEMENTS IN PLANTS

The application of a poisonous solution to the root
might conceivably, through plasniolysis, cause certain
hydrostatic disturbance in the plant. I carried out an
investigation to show that such a disturbance, supposing it
to occur, does not cause any excitation. Thus a solution
of KNO, applied to the root of the seedlings of Mimosa did
not produce any excitation.

In investigations on the effect of poisons, 1 first selected
potassium cyanide, as previous experiments proved it to be
one of the most effective toxic agents. One per cent, solution
of this substance was applied to the root of the Mimosa
seedling in a manner that has already been described. The
nearest motile leaf-indicator was always at a distance of
20 mm. above the point of application. After a certain
interval, tlie poison was found to take effect and the death-
excitation was exhibited by the sudden fall of all the leaves.
I give below the periods found to elapse in four typical
cases, between the application of poison and the exhibition
of excitatory reaction. The initiation of death-excitation
at the point of application itself must have taken place
about four seconds earlier, this being the time lost in trans-
mission through the intervening distance of 20 mm.

T.\BLE LXIII.— PERIOD ELAPSING BETWEEN APPLICATION OF 1 PER CENT
KCN SOLUTION AND EXHIBITION OF DEATH-EXCITATION.

No.

Time.

1

236 seconds.

2

256

3

H)3

t

180

Average

time, 216 seconds.

Experiment 312

THE TRANSMISSION OF DEATH EXCITATION 783

The time necessary for the appearance of death-excitation
will depend, as stated before, on the strength of application
and on the effective virulence of the poison.
With regard to the first, we saw that the
average time taken by 1 per cent. KCN solution to cause
death-excitation was 216 seconds. For observing the
effect of stronger solution, I next applied 5 per cent, solution
to a second batch of seedlings with the following results.

TABLE LXIV. — PERIOD ELAPSING BETWEEN APPLICATION OF 5 PER CENT.
SOLUTION OF KCN AND EXHIBITION OF DEATH-EXCITATION.

No.

Time.

1

42 seconds.

2

60 „

3

61

4

58 „

Average time, 55 seconds.

As regards the relative virulence of different poisons,

I knew from my previous investigations that mercuric

chloride is less toxic in its action than
Experiment 313,. . , _,, . ,

potassium cyanide. The average period

required for exhibition of death-excitation with 1 per cent.

solution of this agent was found to be 650 seconds, as against

216 seconds required for 1 per cent, solution of potassium

cyanide.

Transmitted death -excitation in Biophytum. — The

thin and long flower stalks of Biophytum are very effective

in the conduction of excitation. When
Experiment 314 ,, -• i . 3 • -i. j.-

these are stimulated in any way, excitation

travels downwards, and the sensitive leaflets exhibit

784

LIFE MOVEAJENTS IN PLANTS

successive closures from the centre outwards. For locai
application of poison, a small piece of cloth was wrapped
round the upper portion of the flower stalk which wa&
moistened with a small quantity of 5 per cent, solution of
KCN ; special care was taken that the poison did not leak
downwards. After an interval of three minutes the death-
excitation was initiated which caused the successive closure
of the leaflets. A record of the response of a single leaflet
showed that it was multiple (Fig. 296). After the
cessation of the multiple pulsation, the leaflet was locally
stimulated by a moderate stimulus at the point marked with

Fig. 296 ^lultiple resj)onses ol' leaflet of Biophytiuii iiiuler transmitted
death-excitation due to poisoning.
Local stimulation of the leaflet at cross gave rise to a single response (see text).

the cross. This gave rise to a single response, proving that
the poison did not reach the leaflet ; the multiple response
was thus due to the intense excitation from the distant
poisoned area.

SUMM.\RY.

On subjecting Mimosa to steady rise of temperature in
a bath, a sudden fall of the leaf is observed at the critical

THE TRANSMISSION OF DEATJl EXCITATION 785

temperature of 60°C. This in reality is the death-spasm
of the plant.

In order to show that the movement of the fall of leaf
is not due merely to shrinkage of cells in the pulvinus by
coagulation of their protoplasm, but to excitatory reaction,
the motile organ was kept free from the action of heat, a
distant point lower down the stem being subjected to the
action of rising temperature. At the critical temperature
of 60°C., an excitatory impulse was generated at the dying
portion of tissue, which, travelling upwards, caused the fall
of the leaves. On repetition of the experiment the killed
portion did not initiate any fresh excitatory impulse ; but
exposure of fresh portion of stem to the critical temperature
gave rise to a new impulse. Similar effects were also found
to occur in Averrhoa and in Biophtjtum.

The death-points of motile and ordinary tissues are
found to be practically identical.

Death-excitation is also locally initiated under the
action of poison, and the excitatory impulse is then trans-
mitted to a distance. The period necessary for the initiation
of the excitatory spasm is shortened by the increased
strength and virulence of the poison.

The occurrence of an intense excitatory reaction in the
tissue at the moment of its death, is thus conclusively
proved by the results of experiments on scalding and
poisoning.

LX VIII. —THE SPREAD OF THE
WATEK-HYACINTH.
By Sir J. C. Bose.

Perhaps few pests have caused such a wide devastation
and threatened the economic existence of a country as the
Water-Hyacinth. (Eichornia Crassipses). It is spreading
over large areas in certain States of America, in AustraUa,
Java, Burma, Ceylon and India. The danger is specially
ominous in Bengal ; a few years ago it was growing sporadi-
cally in the eastern district which is one of the most fertile
provinces in India. Its spread is now beyond control ;
many of the smaller rivers and canals are so densely packed
with it that navigation has become impossible. The floods
carry the Hyacinth to the arable lands ; once it gets a foot-
hold there the plants under cultivation succumb in the
struggle for survival. A single root of the Hyacinth has
been known to spread through an area of 600 square metres
in the course of a few months. The economic danger from
the spread of this pest has become very acute and the
Government of Bengal recently appointed a commission
under the presidentship of the author, to enquire into the
subject. Certain preliminary investigations have been
carried out at the Bose Institute in regard to the efficacy
of different methods which had been employed in various
countries to check the spread of the pest. A short account

of the investigation is given below

786

THE SPREAD OF THE WATER-HYACINTH 7«7

In Figure 297 is reproduced a photograph of a stretch
of plant-growth in the large water course adjoining the
Experimental Kesearch Station at Sijbaria on the Ganges.
The weeds grow to a height of more than three feet. The
leaf-stalk of the plant is expanded like a bladder to give it
sufficient buoyancy for floating in water. The wind caught
by the leaves presses the plants against each other ; a compact
mass is thus formed, the plants in the interior being com-
pletely sheltered by those outside. The growth is so dense

Fig. 297 A stretch of Water-Hyacinth, near Sijbaria on the Ganges.

that in many places it is possible to walk over the floating
mass; navigation under these circumstances is an impossi-
bility. The plants have thus spread over rivers, canals,
and shallow stretches of water through many square miles
which are not easily accessible ; this has introduced
additional difficulties to the destruction of the pe«t.

POSSIBLE METHODS OF DESTRUCTION.

The theoretical methods for the destruction of the plant
and the question of their effectiveness are described below.

788 LIFE MOVEMENTS IN PLANTS

Introduction of fungi. — Fungal parasites might be
found which would cause the destruction of the Hyacinth ;
but there is a considerable danger of the fungus attacking
valuable crops.

THE METHOD OF STEAM.

In the United States attempts have been made to
destroy the plant by turning on the steam-hose and thus
scald the plant to death. A similar method has been
employed in Burma ; in certain experiments the nozzle of the
hose was made to touch the plant and the issuing jet actually
split the leaves which were killed as evidenced by the death-
discoloration. But many new leaves came out in the
course of a few days from <he plant supposed to have been
scalded to death. It has since been thought that high
pressure steam might prove to be more effective; this is
however a gratuitous assumption. For I have shown else-
where that the death-temperature of a plant is very definite ;
as determined by the Death-Recorder this point has in-
variably been found to be at or about 60°C. Ordinary steam
of 100°C. is thus 40°C. higher than the fatal temperature ;
there can, therefore, be no necessity for the use of a still high-
er temperature by the employment of high pressure steam.

For the removal of any possible misgiving in regard to
the fatal temperature for Hyacinth, the leaf of the plant
was placed in a bath suitably attached to
xpti linen .) ^^^^ Death-Recorder previously described.
The record seen in Figure 298 was taken, as the temperature
of the bath rose from 50° C. upwards, each dot representing
a rise of 1°C. The death-spasm of Hyacinth is thus seen
to occur, as in other plants, at 60°C.

Setting fire to the plant. — The effect of the still more

drastic method of scitin- lire to the plant was next observed.

Tlie upper part of the plant (loatiug in
Experiment 31ti , , i -ii • e

water was wrapi)ed round with a piece or
cloth soaked in petrol. On setting the cloth on fire, the

THE SPREAD OF THE WATER-HYACINTH 789

plant was burnt to ashes down to the edge of the water.
The submerged portion of the plant, however, sent out fresh
leaves in the course of a fortnight and growth was found
renewed as if nothing untoward had happened to it.

DISCOVERY OF THE CAUSE OF FAILURE.

Large number of tanks in every district of Bengal are
used for irrigation and for supply of drinking water; they
are often overgrown with the Hvacinth. After clearing the

Fig. 298 Determination of the death-poiut of the Water-Hyacinth.
Death-spasm at 60°C is seen in the up-curve.

tanks a new crop of Hyacinth is found to appear in the
course of a few months, though the growth is now less dense
than before the clearing. From this, it is clear that detached
fragments from submerged portion are effective in the
'propagation of the plant.

The above inference was next subjected to experimental

test. The upper part of the plant was cut off and a small

portion of the submerged plant with roots

Experiment 317 i • j i i • ^i c

was buried under mud : m the course ot

7i>0 LIFE MOVEMENTS IN PLANTS

three weeks new leaves sprang up from the detached portion
of the plant.

The failure of the various methods hitherto employed
has arisen from ignoring the important part played by the
submerged portion of the plant in its propagation. The
seeds no doubt germinate under favourable conditions ; but

Fifr. 299 Photograj)}! of R, root and S, stolon of Water-Hyacinth.

this is practically negligible compared with the vegetative
mode cf propagation. The photograi)h reproduced in
Figure 299 shows the subm.erged portion of the plant which
is as large as the part above water. The number of roots
in each plant is as many as 150 or more. In a vertical
section of the plant numerous buds are seen to occur at the

THE SPREAD OF THE W Al ER-HYACTNTH 79 1

axils of tlie leaves; these grow out into horizontal runners,
each of which gives rise to a new plant. Numerous lunners
spring out Iroui a single phint and the vegetative unilti[)lica-
tion is thus extraordinarily rapitl.

It is thus seen that no Dietltod for cradicat\o)\ of the
fK.st <<iii lie suitisfdctonj irlticli does not ensure the destruc-
tion of tin' sufioicryed portion of tlie piiuit.

METHOD OF POISONOUS SI'RAY.

A very large number of poisons are known which, if
pioperly ajiplied. cause the death of the plant. ]'A"en strong
solution of connnon salt is found effective. Attempts
have been made to destroy the Hyacinth plant by spraying
it with poisonous solutions. But for I'easons to be presently
deseribetl, this particular method would prove to be quite
ineffective. The enormotis ai'eas covered by the Hyacinth
are, as already stated, difficult of access; hence j>oW(M-ful
machinery would be required to send the .sprayed solution
to a distance. But there is little chance of the jioisonous
solution effectively reaching an individual plant in the
interior, sheltered by the dense mass outside. A single
plant which escapes the poisoning would become a new focus
for the s^tread of the pest.

Assuniing, however, that the poison did reach the plant,
its application would be found ineffective in causing tlie
destruction of the plant as a whole. Local death of the
upper part of the plant by steam did not, as we saw. kill
the submerged portion. In the case of poison, the sprayed
solution cannot directly reach the plant under water ; the
only possibility for this lies in the conduction of the poison
by the plant downwards, from the leaves to the roots.

Bm my recent investigations on the physiological
machinery for the ascent of sap* have shown that while a

* Bose — Physiology of the Ascent of Sap (In the iircss).
Longmans k Green.

X

7<J2

I.IFR ^lOVKMKNTS IX 1M,ANTS

poisonous or any other solution is easily condiu'ted by the
ascent of sap upwards, it cannot he carried downwards to
the snbinertied roots. Hence application of poison to the
root kills the j)lant throiij^lioiit its length; application of the
poison to the shoot, on the other hand, causes a local death
which does not. normally sj)eaking, spread downwards.
The followinj^ experiments give n striking" demonstration of

Kif^. ;{C)0 KilVct of poison iipjtlied to t lie root of tlio Hviiciinli. 'I'lit-
illustration to the left is the appearance of the plant hefore, to the riylit, after
application of poison.

the different effects of application of poison to the root and
the shoot.

Effect of poison applied to the root of Hyacinth. — The
effect of formaldeyde solution may he taken as typical of
the action of other poisons. .\ vigorous
plant of Hyacintlt seen to the left of the
Figure 300, was afterwards placed with its roots in a 5 per
cent, solution of formaldehyde. The roots absorbed the
poison which rose with the ascent sap and killed the plant
from below upwards; tliis upward march of death was easily
followed by the ad\ancmg death-discoloration which crept

Kxpcriincnl aiS

THE SPRKAD OF THK WATEIt-HYACINTH 79'i

upwards. The plant was killed throughout its length in

the course of from six to eight hours, when it collapsed and

became a mass of dying and dead tissue.

Effect of poison applied to the cut end of tlic stem of

Clirifsantheniitnt.— The effect described above takes place in
all plants. In Figure 301 are seen the
photographs of cut stems of Chrysan-

thcHiKni corondrinnt : one was placed in water, and the other

Kx]itM-iiiu'iiT ;-il!<

Fiir. •Wl PliotoLii'Hplis of cut steams of Chri/.-'ait.tlwiiiii i
and ill a jioisoiioiis solution.

lilartd ill water

in a poisonous solution. The poison ascended with the
sap, and reached the first pair of leaves, which underwent
an immediate collapse. The fall of the other leaves followed
in succession with the ascent of the poison ; the appearance
of the plant thus poisoned to death is seen on the right side
of the illustration.

Effect of poisoning the leaf. — In sharp contrast with
results given above, w^e next observe the effect of the
application of poison to the upper end of the
Hyacinth as is done by spraying of the
poisonous solution. The poisoning is made even more

Experiment 320

794 l.ll'l-: MONI'.MKNTS IN PLANTS

effective l\v eiiclosinp- the leaf in a close-fitting funnel filled
with f()i'inal(leli\ (If solution: tlic lamina became discoloured
and ci'umplcd up hy llic direct action of the poison. There
was. howcxcr, no ti'ansnnltcd effect and no downwar(] inai'cli

FIl;-. .'-iO^ Kffcft (if iKiisDii P :i|iiilic(l to tlic n|i]ici- ]);iiM (iT .sli(,(Ji in llyaciiilli
;iiii| ill Oil nisiuiflii'iini ni. The Inw rr |i;i rt I'cni.-i ins t'li lly ;iii\c.

of deatli. The leaf stalk innnediately helow remained
green and fully ali\e. <J''ig. '.]{)-2.)

I'lficct (if (ipplicdfidii (>l jHiisdii to ih( iijijii'r cud of flic

■shoot. — .V pai'allel ex|)erinie)it was cai'ried out with the shoot

of the ('linjsdHtlicniiini, {\\c up[)er end of

I]\Iiciiiii('iil '.\'2\ 11 I ■ 1 ■ II

which was placed ni a glass tube fdletl with
the jioison. The {)o;son did not woi-k dcwvnwards as was
shown h.y the leaves helow remaiiung green and expanded in
a li\ :ng condition.

The definite results of in\ (»st igations (h^scrihed above
tJMis clear up the obscurity that li;id sui'rounded the sui)ject.
and thi'rebx narrow down the problem to the essenti;il
element, n.imib. the de-truction of tlu' sutiner|_ed portion

THF, SPRKAI) OK I UK WAIKIMI V VCINTFT 7i';>

of the plant wliicli is the most eftVc-ti\c niraiis oT propaj^a-
tion. This t'annot be done with steam or hy spiayiii<i with
poisonous solutions. The only effect ixc means is in the
mechanical collection and destnution. '['here are \arious
possibilities in the economic utilisation of the plant, Croni
which a larp'e portion of the cost of collection could be
recovered.

SKMNKMIY.

The rapid spreail of the W'atei'-Hyacinth is bi'on^ht
about by ve^^et.itive propagation. The sul)mer;L:ed portion
of the plant sends out a lar^e ninnl)er of horizontal I'unners.
each of which gives rise to a new plant.

Steam kills the portion of the plant above water ; the
submerged portion remains alive and thus brings about a
rapid propagation.

Poisonous .solutions applied to the root are carried
upwards with the ascent of sap and thus kill the plant
throughout the length.

Application of poisonous solutions hy means of the spray
causes only the local death of the upper portion of the plant.
The poison is not conducted downwards. The spraying
method is therefore ineffective in the destruction of the
plant.

TAIX.— EESPONSK To M i:(HAXl('AI. STIMULUS
BY YAT^IATION OF K1>KCTRTC RESISTANCE.

By Sir J. ('. Bosk,

Assisted by
N\i!KM)i{\ Xatii Ni:()(i[. ^r.Sc.

Two independent nieans have been described for the
determination of ])hysiological chanj^es induced in tlie plant,
naniely, the meihods of mechanical and of electromotive
response. In addition to these a third method liad already
been employed in my previous work on Comparative l^lectro-
physiolo^y (1007). This method of response by variation
of resistance is considerably extended in the followinpf series
of papers.

T have already shown that all modes of stimulation,
mccliaiiical . clcctJ'ic, or photic, induce an identical excitatory
effect, as recorded by the mechanical and the electromotive
response. Tlie above will be found fully sup]iorted by the
^letliod of Tvesistivity variation wlucli will he sc|)arately
einploNcd for iii\t'sti;4ations on r'cspoiisc' (!• to mccliaiiical
stimulus, (2) to electric stimulus and ('■]) to the stiundus of
light. Of these the mechanical stimulus has certain advant-
ages, since n the first stage of the inquiry it is preferable to
employ a non-electrical mode of stimulation h)r obtaining
response by variation of electric resistance. The drawback
in the employment of mechanical stimulus is the difficulty
in obtaining stinndi of equal intensity in succession or in
increasing it in a graduated manner. The above difficulties

70<>

Ki;si'()NS|-. UY VAHIA'IION OK HESISTANCE 797

liMve. liowever, becii completely removed by the invention of
certain devices for nnit'orm stimidation. The necessity for
the maintenance ot successive uniform stimuli is sufficiently
obvious. For it is only by such means that it is possible to
secure uniform responses under normal conditions; the effect
of an external a^ent may then be found from the induced
variation in the amplitude of the normal response.

The advantage of electric stimulation is that the inten-
sity may be maintained constant, or varied from sub-minimal
value. This is a matter of importance, since it enables us
to determine whether the responsive reaction is of the same
sign throughout the whole range of stimulation from the
subminimal to the maximal. The drawback in the appli-
cation of induction shocks as stimulus is the liability of the
leakage of high tension current into the galvanometer circuit,
which would vitiate the result. It is to be borne m mind,
that in obtaining record of electric response we have to
employ a very sensitive galvanometer. It is therefore of
utmost importance to remove all elements likely to disturb
the normal deflection. We shall, however, find that it is
possible, by taking sufificient precautions, to eliminate all
sources of error.

Finally, as regards the photic stimulus, it offers no
difficulty in application. Particular care has, however,
to be taken to keep the metallic contacts made with the
])lant shaded from light, as this might give rise to photo-
electric effect. The stimulus caused by light is obviously
less intense than that induced by tetanising electric shocks.

EXPERIMENTAL ARRANGE^MENTS.

We take stems of various plants and mount them as in
the diagram (Fig. 303). The plant is clamped in the middle,
and its two lengths P and Q form the two arms of the
Wheatstone Bridge ; the electric contacts with the plant are

798 r.IFE M<»VKMENTS IN PLANTS

made l>y HKNiris of two plutiiiiiin pins which are thrust into
the plant. The two otlier aiiiis of the hridge are made by
a rlieostat with a sHdinj^ contact. 'Inhere is a balance when
PS = QH ; successive completions of the battery and galvano-
meter circuits by means of a double contact key (not shown
in the figure^ now cause no galvanometer deflection. But
jf the portion of the ])litnt V undergoes a (hminiition of
resistance, the fact is demonstrated bv the rcsidting deflec-

ViiS. ifll-! Kxiicriiru'iiljii iiictliiHl for ()l)t;iiiiilij^ rcsjioiisc to iiiccli;iiii(;i 1
stimulus liv resistivity vjiriatioii. P and (^ are leiigtlis of |>i;iiit wliic-ii t'oriii
two anus of tlio Uriiliri', of wliicli P alone i.s suhjei-ted to torsional vihratiou
lt_v nie:ius of the revolving' eceentric E, worked bv clockwiu'k. C. 'I'lie two
other arms of the Hrulu'e, U and S, are formed bv the rheostat with sliding
eontaet, seen below

tion, say to the i-ight ; a detlection to the Iclt indicates, on
the other hand, an increase of resistanc(> of T.

The balance is easily secured in tlic follow iu^ maiuier;
the sliding contact of the rheostat is at lir-t phKcd in the
middle, and the resistance of Q graduall.\ dmujiished l).\
moving the platinum contact inwards from the extreme
right. After obtaining an a{)proximate balance the plant is
allowed ;i period of rest for about 1") miinM(>s. after which

RESPONSE BY VARIATTCN OF RHSIS'IAXCE 7'.»'.>

the irritation caused by the pin-prick would be found to dis-
api^ear. A very perfect balance is next oi^tained by the
careful adjustment of the sliding contact of the rheostat.
The electric contacts with the plants are made, as previously
stated, by means of platinum pins: this method of contact
is m practice far preferable to that of the non-i)olarisable
electrode.

The next question which demands our attention is tlie
polarisation caused by the brief passage of the battery

Fi-. .304 Records showing uniformly diminished resistance (up-curvi) on
uniform mechanical stimulation. (Calotropis giganfiaj .

current required for the measurement of the electric resis-
tance. This difficulty was at first overcome by the use of
a rotating cummutator by which equi-alternating current
was sent through the circuit, the polarisation being thus
neutralised. This necessitated the reversal of the galvano-
meter connections at the same time, which was secured by
the employment of a second connnutator mounted on the

SOO I. IKK M()vi-;mknts in im.ants

axis of the first. 1 found later, that tlie use of an ahcriiatinjx
ciiri'eiit was an iiimecessarv refinement, since the polarisa-
tion under the actual condition of the experiment is practic-
ally zero. The storage cell used for the experiment has nu
E. M. F. of two volts; the electrical resistance of the plant
is however more than a million ohms. Hence the intensity
of the current is about '2 x 10 '^ ampere. The fi'alvanometer
attains its maximum deflection in the course of about thi'ee
seconds and the circuit is completed, by tlu> double tappin;^
key, for less than 5 seconds. The polarisation produced by
tiie brief passage of such a feeble current is quite negligible.
It does not in any way affect the uniformity of responses
under successive ecpial stinudations as will be found
demonstrated in the record of responses given in Figure 304.

METHOD OF MI5CHANICAL STIMULATION,

The greatest difficulty which confronts us is in securing
successive stimulations of equal intensity and in increasing
this intensity in a definite manner. The tissue could i)e
stinnilated by a spring tapper but the excitation in such .«
case would have remained localised at the point struck, the
adjoining tissue exhibiting the effect of indirect stimulation ;
it has been shown that the effect of the indirect is of opposite
sign to tliat of ilirect stimulation. Hence the result would
iiave been complicated by the algebraical suimnation of tlx-
two opposite reactions. For avoiding this, it is necessary to
stimulate the wdiole length of the tissinv This has Iteen
secured by the method of torsional vibration.

If after securing the halaiice the arm of the plant V he
slowly twisted, say to the right thiough ')° , the physical
distortion is found to cause no measurai)le
'''"'""""'"" variation in the resistance. But a rapid
torsion is found to give rise to a responsive deflection of the
galvanometer, say to the right, indicating a (lintiiii(ti(ni i>j
resistance. It is the siKhlnntcss of the disturbance which

RESPONSE l?V VAIilATIoN OF KKSIS TANn-: 801

constitutes a stiimilus. If now we produce a sudden twist
of 0° to tlie left, we obtain the same excitatory deflection to
tlie ri<ilit as before. It is not the twist as such. l)ut tlie
sudden mechanical disturbance which causes stinuilation.
The plant is next subjected to a I'apid alternating" torsion to
the right and left through ')° : the response is now found to
be nearly doubled. Torsional vibration is thus found to be
a very effective method of stimulation : the intensity of
stimulus, within limits, is found to increase with the
amplitude of torsional vibration.

Additive effect of stimulus. — Keeping the angle of
torsi(Mial vil)ration constant, the stimulus is found to be
increased with the number of repetitions.
An iiiijioridHt result is tJiat a sniqhj iii-
cffrcticc stiniiihis Jiccoinrs rffcctirc uftrr repetition. Thus
while a single torsional vibration of 2° is ineffective, it
becomes effective after a number of repetitions.
The advantage of this is that with small angles,
there is little physical distortion jjroduced in the tissue.
We have here an instance parallel to the cumulative effect
of repeated electric shocks, a single one of w^hich is in-
effective. The mechanical stimulation is effected by
automatic means ; the end of the plant is fixed in
a torsional clamp, and rapid alternating" torsions are given
to P by means of the clockwork C. Suitable adjustments
are provided for regulating the angle of torsion. After the
clock is fully -wound, a press button releases it, with the
result that twenty successive torsional vibrations are pro-
duced in rapid succession. The responsive deflection
induced by stimulus is recorded on a photographic plate.*

* A feeble E. M. F. is generated at the mid-point of P by
the torsional vibration : there is, however, no electric variation
at the fixed points of contact, and no electromotive force round
the circuit. This is seen in the fact that the deflection produced
by the induced variation of resistance remains the same after
the reversal of the connections of the voltaic cell in the Wheat-
stone Bridge.

•^02 LiFK .M()Vi;mi;nis in I'Lants

INlFOinr RKSPONSE (NDIH; INlKoHM STIMULUS.

A series of uiiitonn responses to constant stimulus

r,i|)|ilit'»l at intervals of 10 mimites is seen in Figure 304.

The experimental specimen was a stem of

K\|icriMMiii 'A\l\ _ /-\ 1 1 1 •

( (iiotropis (ii(i<iiitc(i. Other plants also give
similar results, though some are more sensitive than others.
This sensitiveness is further modified by age, by season, and
by the ))hysi()logical condition of tlie tissue. The responsive
variation iiikKm" stimulus may amount to tiMi per cent, of
the norma I icsista nee.

KFKKC'I' Ol'' AXAKSTHK! ICS.

The |)]iysioI()^ical character of the rt\'^p()iisc is demons-

Fiif. .■{().') KtTcci of clilorutdriu in iniliii'iii'j; cli'prcssioii >>{' ii'spoiiso.

trated by the apj)lication of chloroform vapour. We found
that the cxcitahilitv of a vegetable tissue is
depressed imder the contnuied action ol tins

-anaesthetic The first record (Fig. 305) shows the normal

RESPONSE HY \ MM ATION OF RESISTANCE bO'.')-

response ; chloroform was a|)pl!e(l at tlie point mai'ked with
an arrow, the suhsequent responses being obtained at
intervals of 10 minutes. Tlie lesponse by variation of resist-
ance is tlius seen to undergo a decline under the coutintied
action of the ajiaestlu^ic.

PHELTMINARY I'.FFKCT oi- ItlllTK VAPOT^H OF rHr.OliOFOim.

llic sptirk record. — The galvanometric recoids given
above were ()l)tained 1)\ |)liotographic means witli the
inconvenience inse})aral)le froiu working in a dark room. A

Fig. ;W(i Till' sjinrk rccunl <if iiiilvaiidiiictnc ivs]iniisc. Diluif v;i|)(jiii-
of chloroform !i|i|p|ic(l ;tt mrow imliiccil ;i inclitiiiiKny .■iiliiniicincur (if
response followed liy <ie|iresMuii.

different method has. however, been devised for obtaining
direct record of tlic deflection of the galvanometer index ou
a moving piece of paper which is perforated by electric
sparks. A full description of the apparatus will be found
in a subsequent chapter. .V record obtained by the spark-
method is seen in Figure MOO.

We found certain characttristic effects of chloroform

which depended on the duration of application. The

iimiiediate effect at the first stage was found

hx|)eriiiieiit ;{:^(i '^

to be an enhancement of excitabilitv.
followed at the second stage by a depression. In the present

804 l.ll'K MOVKMKNTS IN in.ANTS

experiment, the Hrst lour are the noriiial aiul uiiiroini
responses; the next record was obtained alter a minute of
tlie introduction of tlie chloroform vapour. The response
is seen to have undergone a marked enliancement. Conti-
nued action of chloroforni, however, caused the subsequent
<iepressi()n (Fig. 'M)()).

sl;mmai;y.

The res{)onse to meehanieal stimulu.s is obtained l)y the
■em[)loyment of the W'heatstoni ]iridge, the plant forming
the two arms of the bridge; the othei" two arms are made
^)f a rheostat with sliding contact lor the a<ljustnient of
balance.

Torsional vibiation is shown to be an effective means
<jf stinndating the tissue. The intensity of excitation is
increased by increasing the angle of torsion.

The effect of stinudus is found to be additive; a singly
ineffective stinudus tinis becomes effective by repetition.

The effect of niechanical stinudus is to induce a diminu-
tion of the electrical ivsistance of tiie tissue.

The physiological character of the response is demons-
trated by the action of an anaesthetic like chloroform vapour.
During the first stage of its action, the amplitude of response
is enhanced; continued action of the anaesthetic is, however,
followed l)y a depression.

TAX.— EESISTRITY VARIATION IN PLANTS

UNDEE ELECTEIC STIMULUS.

By Sir J. C. Bosr.

Assisted by

(ilHUPRASANNA DaS, J^.]\LS

A generalisation has previously been established that
all modes of stimulation, mechanical, electrical or photic,
give rise to similar excitatory reaction. ^lechanical stimulus
lias already been shown to induce this, by a diminution of
electric resistance. We shall in the present chapter study
the effect of electrical stimulus in inducing a responsive
variation of the resistance of the tissue.

The gTeat advantage of electric mode of stimulation is
in its constancy and in the wide range of its possible varia-
tion. The stimulus may thus be increased from zero to a
maximum. In the former, the secondary coil is at a very
great distance from the primary, and in the latter it is
pushed in so as to enclose the primary coil. The duration
of application of stimulus can be accurately regulated by
means of a metronome ; in the following experiments tlie
duration of stimulus is half a second.

THE METHOD OF EXPERIMENT.

The experimental arrangements are shown in Figure
307. Two platinum pins are thrust about o cm. apart in
the middle portion of the plant growing in a pot. Records
are taken of the variation of resistance induced by stimulus

80.5

s I ;

LIFE MOVEMENTS IN PLANTS

in this i»aiticular poi'tion ol' the plant which forms the fourth
arm of the Wheat stone's ]3ridge. The electric shock from
the in(hicti())i coil is passed through the length of the plant.
between the tip and the root, tlnis causing uniform stimula-
tion 1)1' iht' intermc(haie poition of the plant.

In ol)taining eleetroUK^tive response of Miino.'yii. the
electric stimulus was applied at some distance fi'om the

l-'i^r. 807 Metlioii of resistivity variation i'or response to ekiirir
f^tiimilus. Pressure of tlie tiltinvr ki v T eanses stiiinilat ion of the plant
liy induction sliock from coil S al tlie time wlicn Lralvanmnetci' circuit is
cut off (see text).

])ulvinus the upj>er and lower halves of which were connected
with the galvanometer. The interposition of a chocking
coil was then h)und effective in preventing the leakage of
the shock-current into the galvanometer circi^it. In the
present case, the electric stimulation is direct and the
prevention of the leakage of the shock-current presents

RESISTIVITY VARIATION IN PLANTS 807

certain difficulties. These are, however, completely removed
by cutting off the galvanometer connections with the plant
during the passage of the induction shock. The shock-
circuit S had, moreover, to be cut off from the plant during
the determination of the resistance and its induced variation ;
otherwise the coil S would have acted as a shunt.

The method of procedure is therefore as follows : The
key K is closed and K j and K 2 opened. The exact balance
is obtained by the sliding contact by which the ratio of P
and Q is varied. The balancing condition is found from the
galvanometer deflection being reduced to zero. The plant
is now cut off from the galvanometer and put on in the shock
circuit; this is done by opening the key K, and closing Kj ;
Kj is simultaneously closed so as to short-circuit the galvano-
meter. The electric shock is thus allowed to pass through
the plant for half a second after which K j and K g are
opened and K closed. The variation of resistance induced
by stimulus, causes an upset of the previous balance of
resistance with the resulting deflection of the galvanometer
spot of light.

In practice, the successive manipulations of making,
breaking and remaking of the connections are performed
almost automatically by a momentary pressure on the tilting
key T, and the release of that pressure. The relative
position of the three keys and the sequence of their action
will be understood from the illustration at the upper corner
of Figure 307.

In the following investigations, intact or cut specimens

of various plants have been successfully employed ; among

these may be mentioned the seedling of Helianthus amiuus

and of Impatiens, also the climbing stem of Ipomea

pulchella, and Porana paniculata. The sensibility depends

on age, season, and the previous history of the plant. Under

favourable circumstances very pronounced response is

0

808 LIFE MOVEMENTS IN PLANTS

obtained under an electric shock so feeble as to be beyond
human perception.

After making suitable electric connections by means of
platinum electrodes, the specimen is allowed a period of rest
for complete subsidence of irritation caused by manipula-
tion. The characteristic responses by variation of electric
resistance are then obtained under sub-minimal, moderate
and strong stimulations.*

EFFECT OF STIMULUS OF MODERATE INTENSITY.

The intensity of stimulus is continuously increased by

the approach of the secondary coil to the primary till a

particular distance is found at which the

Expcriincut 327 ^■ -, p • 1 , ,i

amplitude or response is about three centi-
metres. The duration of electric stimulation is only half a
second, and successive stimuli of equal intensity are applied
at intervals of eight to ten minutes. Figure 308 shows : (1)
that the response is by a di7ninution of resistance as indicated
by the up-curve, (2) that the recovery is complete on the
cessation of stimulus, and (3) that the amplitudes of
successive responses are iequal under uniform stimulation.
If successive stimulations are at shorter intervals than 5
minutes, the protoplasmic recovery is incomplete, and we
observe signs of fatigue. This is shown by a diminution in
the amplitude of successive responses. Another interesting
phenomenon, sometimes observed, is the occurrence of
alternating fatigue, that is to say, a large response is followed
by a small one, and this, in a recurrent series,

* An autonomous pulsation is sometimes observed, due to
the pulsatory activity of certain cells which maintain the ascent
of sap. The electric pulsation may, however, be made to dis-
appear by separating the points of contact on the stem, till the
pulsatory activities at the two points are in the same phase.
A detailed account of the phenomenon will be found described
in the Physiology of the Ascent of Sap to be shortly published
by Messrs. Longmans. In all experiments, the isoelectric
condition of the two contacts is assured by observing the
quiescent condition of the galvanometer spot of light.

RESISTIVITY VAHIATION IN PLANTS 809

For the study of the effect of external agents, it is
important that the normal responses should be uniform, and
the conditions for securing such uniform responses have
been fully described. The stimulating or depressing
character of an agent may now be discovered from the
induced modification in the normal response ; an enhance-
ment of excitability thus will be detected by a concomitant

FIG. 308 FIG. 309

Fig. 308 Effect of stimulus of moderate intensity. Response by
diminution of resistance seen in the up-curve.

Fig. 309 Effect of sub-minimal stimulus. Response by increase of
resistance exhibited by the down-curve (HelianthusJ .

increase in the amplitude of response; a lowering of excita-
ability will, on the other hand, be indicated by the amplitude
of response undergoing a depression.

EFFECT OF SUB- MINIMAL STIMULI.1S.

We have seen that the sign of response under sub-
minimal stimulus is opposite to that of the normal. Thus,
while moderate stimulus induces a retardation
of growth, sub-minimal stimulus induces an
enhancement of the rate, (p. 224). In the electromotive

810

LIFE MOVEMENTS IN PLANTS

method, the response under feeble stimuhis is galvanometric
positivity, instead of the normal negative. In Mimosa
feeble stimulus indiK-es an expansive erectile response in-
stead of the coiitractih' fall of tli(> leaf, (p. 147). This positive
response is more easily observed when the critical point of
transition from positive to negative becomes raised by the
subtonic condition of the tissue.

It is very remarkable that in the method of resistivity
variation we also obtain, under feeble stimulation, a response
of oj^osite sign to that of the normal ; that is to say, the

Fig. 310 Multi])le rcsj)onse to strong electric and thermal shocks.

resistance of the tissue exhibits an increase, instead of the
normal diminution. Figure 309 shows such positive res-
ponses under feeble stimulus, by an increase of resistance
(down-curve) followed by recovery.

EFFECT OF STRONG STIMULUS.

If the intensity of stiffnulus be gradually increased, the

amplitude of normal negative response by diminution of

resistance becomes enhanced till a limiting

Experimciif .T29 ^

value is reached. Further increase of
intensity is then found to give rise to the very interesting

RESISTIVITY VARIATION IN PLANTS 811

phenomenon of multiple response, the resistance of the
tissue undergoing' a recurrent variations, analogous to the
multiple mechanical and electromotive responses under
strong stimulus.

As the strong stimulus gives rise first to a very large
response which is followed by a multiple series, it is difl&cult
to obtain a complete record since the first response goes off
the photographic plate. It is, however, easy to observe
them by watching the alternate movements of the galvano-
meter spot of light which persist for a considerable length

Fig. 311 Effect of Co, in depressing response by resistivity variation.

of time. It has sometimes been possible to obtain the
multiple response within the plate, by employing a stimulus
which is not excessively strong. The record seen to the left
of Figure 310 shows five multiple responses, under moder-
ately strong electric stimulus ; the record to the right of the
figure shows multiple response under thermal stimulus. I
have also obtained similar multiple responses under the
stimulus of strong light.

Having studied the responses under feeble, moderate
and strong stimiili we shall next observe the characteristic

812 LIFE MOVEMENTS IN PLANTS

effects of physiological change induced by the action of
anaesthetics.

EFFECT OF CARBON DIOXIDE.

We found that prolonged application of carbon dioxide

induces a depression of all modes of response.

The method of resistivity variation also

Experiment 330 ii-,-it • p -r

exhibits similar depression ot response. In
Figure 311 the first two responses are normal ; the introduc-
tion of carbon dioxide into the plant-chamber is seen to
have induced a marked depression.

EFFECT OF ETHER AND CHLOROFORM VAPOUR.

Dilute vapour of ether has already been found to induce

Fig. 312 Effect of dilute ether vapour in enliancing the response by-
resistivity variation.

a marked enhancement in the mechanical and the electro^
motive response. The response by resistivity

Experiment 331 ..,,.,. . ,

variation also exhibits a great increase under
the action of this anaesthetic (Fig. 312). The enhanced
excitability under dihite chloroform vapour is so great that^

RESISTIVITY VARIATION IN PLANTS 813"

a single stimulus often gives rise to a multiple series of

responses.

SUMMARY.

The response of normal tissues to electric stimulus is by
a diminution of electrical resistance, followed by a recovery.

The response to sub-minimal stimulus is of an opposite
sign to that of the normal, i.e., an increase of resistance
instead of a diminution.

Strong stimulus gives rise to a multiple series of
responses by resistivity variation.

Prolonged action of carbon dioxide induces a diminu-
tion in the amplitude of response.

The various characteristics of response by resistivity
variation are parallel to those of mechanical response of
sensitive plants, the responsive variation of growth in
growing organs, and the response of electromotive variation
in all vegetable tissues.

Dilute ether vapour causes a great enhancement in the
response. The excitability of the tissue is also increased by
dilute vapour of chloroform, on account of which a single
stimulus is often found to give rise to repeated responses.

LXXI.— THE QUADEANT METHOD OF RESPONSE
TO STIMULUS OF LIGHT.

By Sir J. C. Bose,

Assisted by
Apurba Chandra Nag, M.Sc.

We have found in the two previous chapters that modes
of stimulation, as diverse as mechanical and electrical, induce
an excitatory reaction exhibited by an induced diminution
of resistance. We shall now study the effect of the stimulus
of light on the resistance of the tissue ; a new method of
very great sensitiveness has been devised for this investiga-
tion, so sensitive indeed as to detect the effect of light of
so brief a duration as a hundred thousandth part of a
second. This is due to the fact that the galvanometer
deflection by this method is not simply proportional to the
induced variation of resistance of one arm, but to the
product of variations in two arms.

The principle of the method will be understood from
the diagram given at the lower end of Figure 313, which
represents a leaf blade of Tropaeolum in which its four
quadrants P, Q, E, S, serve as the four arms of a Wheat-
stone Bridge. The diagonal connections are made with the
battery and the galvanometer respectively. The three
contacts with the leaf may be fixed, and the fourth moved
slightly to the right or to the left till an exact balance is
obtained in darkness, when PQ=RS. One of the
pairs of opposite quadrants P and Q is shaded by a double

814

THE QUADRANT METHOD OF RESPONSE 815

Y-shaped screen. Exposure of the leaf to Ught produces a
variation of resistance not of one, but of two opposite arms
of the bridge K and S ; the upsetting of the balance is thus
due to the product of the variations of resistance in the two
opposite quadrants. The responsive galvanometer deflec-

Fig. 313 The Quadrant Method for determination of variation of electric
resistance. Two opposite quadrants of the leaf are shaded. Electric
connections are made at the junctions of the quadrants (see text).

tion in a particular direction is found to be very large and
indicates a diminution of resistance in the quadrants
stimulated by light. The double V-shaped screen is next
turned through 90°; the quadrants P and Q are now exposed
to light, and K and S shaded from it. The resulting upset

816 LIFE MOVEMENTS IN PLANTS

of the balance and the galvanometer deflection is now in ar>
opposite direction.

The reliability and the sensitiveness of the Quadrant
Method may thus be tested by obtaining equal and opposite
responses under alternate illumination of the two pairs of

Fig. 314 Equal responses in opposite directions by alternate
illumination of the two pairs of quadrant,

quadrants ; the test in confirmation of the above will be
found in records given in Figure 314.

After securing such perfect adjustments, the double V-
shaped screen is kept fixed, and the leaf mounted in a
rectangular dark chamber closed except at the front, which
carries a photographic shutter by which one pair of quadrants
is exposed to light for a definite duration. The electric
connections with the leaf are led to four binding screws ; the
petiole protruding from the box is dipped in an U-tube filled
with water, (cf. right-hand illustration of Fig. 313).

THE QUADRANT METHOD OF RESPONSE 81T

The source of light is in an arc or an incandescent lamp,
placed inside a lantern, the condenser of which sends a
parallel beam of light. A rectangular glass trough filled
with alum solution is interposed in the path of light to-
absorb the heat rays. The duration of exposure is varied
according to the sensitiveness of the specimen; the usual
period of exposure is about 20 seconds.

RESPONSE TO LIGHT FROM A SINGLE SPARK.

The extreme sensitiveness of the quadrant n-fcethod will

FIG. 315 FIG. 316

Fig. 315 Response to light from a single spark.

Fig. 316 Effects of stimulus of light increasing in the ratio of 1 : 3 : 5 : 7.^

be found fully demonstrated in the record given in Figure
315. The duration of a spark at the dis-

Experiment 332 , „ ^ ^ ^ , , ,

charge of a Leyden Jar may be regarded as
©f the order of hundred thousandth part of a second. The
discharge took place at a distance of 15 cm. from the leaf

818 LIFR MOVEMENTS IN PLANTS

and the response is seen to consist of a priliminary positive
twitch followed by a lar^e negative response, indicative of
normal diminution of resistance. The leaf exhibited a
complete recovery.

EFFECT OF INCHEASING INTENSITY OF LIGHT.

The arc lamp is taken out of the lantern, and the

diverging beam employed for the following experiment. As

the intensitv of light varies as the square of

Experiment 333 , ,. • i i i ^

tiie distance, suitable marks were made on
the scale fixed on the tab'e, so that the intensitv of light

Fig. 317 Effect of carbonic acid gas on response to light.
Note preliminarj- enhancement followed bj' decline.

incident on the leaf was increased in the proportion of 1 : 3 :
5 : 7 by bringing the arc nearer the leaf at the particular
distances marked on the scale. The duration of exposure
was kept the same.

The responses under increasing intensities of light in
the ratio given above are seen in Figure 316. The resistance
is seen to undergo a diminution with the increasing intensity
of stimulus.

THE QUADRANT METHOD OF RESPONSE 819

We shall next study the eifects of anaesthetics on
response to the stimulus of light.

EFFECT OF CARBON DIOXIDE

After taking a series of normal responses, carbon dioxide

was passed into the plant-chamber. This is seen to

give rise to a preliminary enhancement of

Experiment 334 p n i i • • j

responses followed by increasmg depression.
(Figure 317). The effect of. carbon dioxide is thus the same
on all responses under diverse modes of stimulation.

EFFECT OF DILUTE VAPOUR OF CHLOROFORM.

Dilute chloroform has been shown to induce a prelimi-
nary enhancement of response followed by a decline. This
anaesthetic is seen to induce a similar effect
on response to light ; after the introduction
of the chloroform vapour, the three successive responses are

Fig. 318 Effect of chloroform. The preliminary enhancement
was followed by a depression.

found to be increased by about 50 per cent ; the subsequent
responses exhibit a great depression (Fig. 3i8).

-820 LIFE MOVEMENTS IN PLANTS

VARIATION OF PERMEABILITY UNDER STIMULUS.

The excitatory fall of the leaf of Mimosa is due to the
•expulsion of the sap from the excited cells in the pulvinus.
This may be due to an active contraction or to an increase
of permeability of the protoplasmic lining of the cell. Our
present state of knowledge in regard to the mechanism of con-
traction of vegetable tissue is as incomplete as that of the
phenomenon of muscular contraction. According to Schafer,
the contraction of a muscle is brought about by a transfer
and redistribution of fluid material ; the contraction of the
pulvinus of Mimosa is also due to the transfer of fluids. All
movements of living organism whether animal or plant may
be said to be effected by essentially the same means, i.e.,
by the contractile protoplasm, of which the highly special-
ised form is seen in the muscular tissue of the animal.

It has been supposed that the mechanical response of
the pulvinus is not due to active contraction, but to the
escape of water from the distended cells by an induced
increase of permeability. The observed diminution of the
•electric resistance of vegetable tissues under stimulus may
be regarded as offering some support to the theory of increase
of permeability under stimulus.

The high resistance of a tissue has been imagined to
be due to the impermeability of the cell membranes to salts,
the salt solution being conductors of electric current. The
diminution of resistance after stimulation is regarded as due
to increase of permeability and resulting escape of fluid
containing salts, which confers increased electric conduc-
tivity or diminished resistance of the tissue. But this
theory does not explain all the facts ; (1) for the escape of
sap in one direction would produce an increase of conduc-
tivity, more or less persistent. But the normal resistance
is found restored in the course of as short a time as 2

THE QUADRANT METHOD OF RESPONSE 821

minutes ; (2) it does not explain a temporary increase of
resistance, which is often found to be the al^er-effect of a
stimulus (see Fig. 308) ; (3' it offers no explanation of the
multiple response under strong stimulus, where we observe
a recurrent diminution and increase of resistance ; (4) and
finally, the increase of resistance induced by feeble stimulus
is a further and insuperable difficulty in the way of the above
theory.

The permeability variation, according to the above
theory, is regarded as selective or one-directioned, by which
the fluid is expelled outicards from the cell. But this is
not a correct interpretation of fact, for there is an alternat-
ing phasic change on account of which the sap is not merely
expelled outicards, but also absorbed inwards; instead of
selective permeability in one direction, there are, as it were,
alternate directioned changes by which the fluid is period-
■ ically expelled and taken in across the boundary of the cell.
This is clearly seen in rhythmic cells of the lateral leaflets
of Desmodium gijrans, where the recurrent down and up
movements of the leaflets are associated with periodic
expulsion and absorption. This is also the case in the pro-
pulsion of sap in plants, which I have shown to be caused
by periodic expulsion and absorption of fluid by the active
layer of cells in the cortex.

This periodic expulsion and absorption is the common
characteristic of all modes of response ; I have shown that a
continuity exists between the autonomous, the multiple,
and ordinary response. In multiple responses under strong
stimulus, {e.g., in Biopytum leaflet) there is produced a
recurrent contraction and expansion concomitant with the
periodic expulsion and absorption. The single response
under stimulus in ordinary cases also exhibits this periodic
change of expulsion with subsequent absorption during
recovery .

822 LIFE MOVEMENTS IN PLANTS

The facts described above indicate that a simple
theory of permeabihty-variation is not sufficient for a
full explanation of the observed phenomena. These and
other results point rather to the existance^ of two definite
protoplasmic reactions, which may be described as the A- and
the D-effects. The A-cffect, usually induced by sub-minimal
stimulus, finds outward expression, by induced expansion,
increase of turgor, enhancement of the rate of growth,
galvanometric positivity and increase of electrical resistance.
The D-eifect (predominantly induced under stimulus of
moderate intensity) is outwardly manifested, on the other
hand, by contraction, diminution of turgor, diminished rate
of growth, galvanometric negativity and diminution of
electric resistance. The following table shows the parallel
effects exhibited by diverse modes of response.

TABLE LXV. — SHOWING PARALLELISM IN DIFFERENT MODES
OF RESPONSE.

External
chan<re

Mechanical
response

Variation of
growth

Electromotive
response

Resistivity
variation

Sub-minimal
stimulus '

Expansion ;
erectile
response

Acceleration
of growth

Galvanometric
positivity

Increase of
resistance

Moderate
stimulus

Contraction ;

fall of leaf

Multiple
response

Retardation

of growth

Galvanometric

negativity

Diminution of
resistance

Strong
stimulus

Multiple
response

Multiple
response

Multiple
response

Carbonic

acid gas

Diminished
response

Diminished

res))on8e

Diminished
response

Diminished
response

Vapour of
ether

Enhanced
response

Acceleration
of growth

Enhanced
response

Enhanced
response

THE QUADRANT METHOD OF RESPONSE 823

SUiMMARY.

In the Quadrant IMethod for determination of variation
of resistance under the stimulus of light, the quadrants of
the lamina serve as the four arms of the Wheatstone Bridge.
One of the two pairs of opposite quadrants is shaded by a
screen. Exposure of the other pair to light gives rise to a
responsive variation of resistance.

The method is found to be extremely sensitive, response
being obtained of the effect of light from a single spark.

The response to the stimulus of light is b}' a diminution
of resistance, followed by recovery on the cessation of light.

Increasing intensity of light induces a corresponding
diminution of the resistance of the tissue.

Anaesthetics like carbon dioxide or dilate chloroform
induce a preliminary enhancement of response followed by
depression.

All modes of stimulation, mechanical electrical or
photic, give rise to similar response by diminution of electric
resistance.

Feeble stimulus gives rise to the opposite change of an
increase of electric resistance.

A phasic change is observed by which the sap becomes
alternately expelled from, and absorbed by, the cell. The
expansion under feeble stimulus is associated with absorp-
tion and contraction under stronger stimulus, with
expulsion.

The indications of effects induced by external change
given bv the method of resistivity variation are similar to
those obtained from responsive variations of electromotive
force, of the rate of growih, and of mechanical response.
They are thus different expressions of the fundamental
protoplasmic change in response to external variation.

824 LIFE MOVEMENTS IN PLANTS

These changes may be generally described as the A- and
the D-effects. The former is exhibited by expansion,
enhancement of the rate of growth, positive electromotive
change and the increase of resistance ; the latter is expressed
by contraction, retardation of growth, galvanometric
neffativitv and diminution of electric resistance.

LXXII.— THE SELF-KECOEDING EADIOGKAPH.

By Sir J. C. Bose,

Assisted by
Naeendra Xath Xeogi, M.Sc.

A diurnal periodicty is generally exhibited in the various
activities of the plant ; a daily periodicity is also shown in
the movements of different plant organs. These diurnal
periodicities must be related to the daily variation of tem-
perature and the recurrent changes of light and darkness ;
they must be thus brought about by the algebraical
summation of effects induced by variation temperature
and of light. It would thus be impossible to analyse the
phenomenon unless a continuous record of changes in the
intensity of light is secured with the same exactitude as the
variation of temperature. As regards these two factors, the
effect induced by the rise of temperature is often antagonistic
to that of increasing intensity of light. Thus a rise
of temperature enhances the rate of growth up to an
optimum ; light, on the other hand, acts as a stimulus retard-
ing the normal rate of growth. Variation of temperature
affects the organ as a whole, whereas light may act unilater-
ally, depressing the rate of growth of the particular side
subjected to the action of light.

For a full analysis of diurnal periodicity in plants, it
thus becomes necessary to devise means for continuous record
of variation of temperature and the changing intensity of
light. As regards variation of temperature, a simple and

825

820 LIFE MOVEMENTS IN PLANTS

reliable tj'pe of thermograph was described in one of the
volumes of this series, by which it is easy to obtain a con-
tinuous record of the variation of temperature throughout
the day and night. No apparatus is, however, available at
present for the continuous registration of variation of the
intensity of light.

THE SELENIUM CELL.

The method for oi)taiiiiiig record of intensity of light
and its variation depends on utilising" the property of a sub-
stance sensitive to light. Selenium is well known for
the characteristic diminution of its electric resistance under
illumination. Thus a definite deflection is produced in a
galvanometer when the selenium cell is placed in the dark
in series with a battery of voltaic cells. Exposure to light,
causing a diminution of resistance, gives rise to an increase
of deflection. The variation in the deflection of the galvano-
meter thus indicates the variation in the intensity of light.
Several difficulties are, however, encountered in practice
in obtaining a continuous record for the whole day.
The resistance of selenium undergoes a change under
the continued action of an electric current; this is due
to polarisation caused by the current, which increases with
the strength and the duration of the current. But the effect
of polarisation is negligible, if the current be feeble and of
short duriition. Another difficulty, which might possibly
interfere with the accuracy of the readiuiis is tbe effect of
daily variation of temperature on the normal resistance of
the selenium cell. This effect may be eliminated by observ-
jng, at different hours of the day, the difference of the
resistance of the cell (1) in the dark, and (2) after exposure
to light. FinaJly, we have to devise some means for auto-

SELF-RECORDING RADIOGRAPH 827

)f th(

intensities of lii^ht.

ma tic record of the galvanometric deflection under changing

THE RADIOGRAPH.

The difficulties enumerated above have been completely
removed by the following devices :

a. The Wheatstone Bridge for balancing electric resist-
ance of the selenium cell in dark and its upset on exposure
to light.

b. The arrangement of three electric keys which are
automatically put on and off in regular sequence and at pre-
determined intervals.

c. The Self-recording Galvanograph.

THE WHEATSTONE BRIDGE

This is diagrammatically represented in B, (Fig. 319).
The resistance of the particular selenium cell S is 76,000
ohms in the dark. An approximately equal resistance is
placed in the second arm of the bridge. A rheostat having a
large number of turns of fine wire with a sliding contact is used
for the two variable arms of the bridge, diagrammatically
represented by a straight line. An approximate balance is
obtained when the sliding contact is in the middle ; a slight
movement to the right or to the left secures the exact balance
when the galvanometer deflection is reduced to zero. The
balance is upset when the selenium cell is exposed to light
and the resulting deflection gives a measure of the intensity
of hght.

THE AUTOMATIC KEYS.

After previous adjustment of the balance in the dark
the electric circuit is completed by the closure of key K i after
which the selenium cell is exposed to light by an automatic

828 LIFE MOVEMENTS IN PLANTS

electro-magnetic shutter. The deflection of the galvano-
meter is recorded on a piece of moving paper by means of
electric sparks. These different operations are carried out
in proper sequence by the automatic devices described below.
K , completes the battery circuit for about 10 seconds,
by "uliich time the record is completed. The successive
records for variation of light are taken at intervals of 15

Fig. 319. The Self-reeordinp: Radiograph.

The gelenium cell, S, is pcrioilieaily exposed to light by the electromagnetic
shutter, T. The selenium cell forms one arm of the Wheatstone Bridge, B
The three keys, Ki, Kj, K3, are periodically closed and opened by clockwork.
G, the recording galvanometer with index, I, carrying double-pointed plati-
num at its end, which moves between the metal strip, C, and the plate, M.
R, sparking coil with its electrodes connected with C and U The battery
is not shown in the figure (see text).

minutes ; the periodic closures of the circuit are thus for 10
seconds at intervals of 15 minutes. In practice this short
passage of the current is found to cause no polarisation.

The second key K ., actuates an electromagnetic device
by which the trap-door, T, is opened for the definite period of
one second ; the selenium cell S inside the dark box is thus
expo.?ed to light for tliis length of time. The trap-

SELF-RECORDING RADIOGRAPH 829

door is seen in the diagram immediately above the dark box.
In reahty it is at the upper end of a vertical tube the inside
of which is coated with lamp-black to prevent side reflection.
The light that falls on the selenium cell is thus from a
definite area of the sky. The intensity of light from the
sky at different periods of the day causes deflection of the
galvanometer which is proportional to that intensity. The
maximum deflection of the galvanometer employed is
attained in the course of 3 seconds after the exposure.

The third key Kg is for completion of spark circuit R for
record of the maximum galvanometric deflection, three
seconds after the exposure of the selenium cell. This key
actuates a sparking coil R, the vibrating interrupter of
which is not shown in the figure. The spark, thus
produced, punctures the maximum deflection of the galvano-
meter index on a moving piece of paper attached to the
plate M.

The successive closure and opening of the keys are made
automatically and in proper sequence by means of a clock-
work, the whole process being repeated at intervals of 15
minutes.

THE GALVANOGRAPH.

We now come to the most difficult problem concerning
the automatic record of the galvanometer deflections. This
may be secured without great difficulty by means of photo-
graphy. A spot of light reflected from the galvanometer
mirror may be allowed to fall on a photographic plate which
descends at an i niform rate by clockwork. This, how^ever,
entails the use of a dark room and subsequent development
of the plate. The trouble was avoided by the device of
direct record of the galvanometer deflection by means of
electric sparks.

The sparking method has been previously employed in
which the deflected index of the galvanometer in connec-

880 LIFE MOVEMENTS IN PLANTS

tion witli one electrode of an induction coil leaves a spark
record on a moving piece of paper. Several diflQculties are,
however, encountered in the employment of this method with
a highly sensitive galvanometer. There is a liability of
leakage of the high tension current into the galvanometer
circuit. Secondly, the discharge of the spark gives a back-
w^ard kick to the index by which the normal deflection
undergoes an unknown variation.

The above difficulties are removed in the following
manner. The moving coil of the sensitive D'Arsonval
galvanometer, has a long glass index I, at right angles to
the plane of the coil. The glas^ index is coated with shellac
varnish to render it higldy insulating. The index is pro-
jected to a short distance on the opposite side, for attach-
ment of a counterpoise ; this takes the form of a vertical vane
of mica which acts as a damper. The gahanometer itself
is of an aperiodic type, and the addition of the damper makes
it perfectly dead-beat. The sensitveness of the galvano-
meter is such that a micro-ampere of current produces a
a deflection of 10 mm. of the index. The recording index
has attached to it a short vertical piece of thin platinum
wire pointed at its two ends ; this end of the index moves
between a sheet of metal M, and a semi-circular piece of
narrow metal sheet C. The metal sheet M is mounted on
wlieels and move.s at an uniform rate bv clockwork. Eecord
is made by sparks. One electrode of the sparking coil is in
comicction with C, and the otlicr with '\\ . The sparking
thus takes place simultaneously, above and below the
vertical and double-pointed platinum wire carried at the end
of the index. There is thus no resultant kick, and the index
remains undisturbed. The sparking, as previously stated,
takes place three seconds after exposure of the selenium
cell to light, by wliich time the deflection reaches its
maximum. The record thus consists of successive dots at

SELF-RECORDING RADIOGRAPH 831

intervals of 15 minutes, the dots representing the maximum
deflections of the galvanometer corresponding to the
intensity of light.

The record given in Figure 820 was taken about the
end of Januarv ; the sun rose at about 6-45 a.m. and set at

Fio- 320 Radiograph of variation of intensity of light from the sky
during 12 hours in winter. The upper record shows the variation on a
brio-ht dav the maximum intensity being attained at 12 noon. The lower
record exhibits irregular variation on a cloudy day. The horizontal record
above the base line shows that the electric resistance of selenium cell is
practically unaffected by variation of temperature. Successive thin dots
at 15 minutes' interval, thick dots at intervals of an hour.

5-30 P.M. The twilight is very short in the tropics ; the sky
is feebly lighted about 6 a.m. ; it becomes dark about
6 P.M. The record shows the intensity of light to be exceed-
ingly feeble at 6 a.m. The rise in the intensity was rapid.

832 LIFE MOVEMENTS IN PLANTS

attaining the maximum at 12 noon. This wih be designated
as the hght-noon. The intensity of hght then declined at
a rate slower than the rise. But after 5 p.m. the fall of
intensity was extremely rapid.

It was stated that there is a possibility of change of
resistance induced by diurnal variation of temperature. In
order to determine the extent of this variation, a spark
record was also obtained before exposure to light. The

/

'^'A

1 ' 1 ' ! ' 1 ■

6aan. 9

1 ■ 1 'I ' 1 '
a.

VOOH

3 6p.fn. 9 tSi 3 €a.m.
^ MIDNIGHT

Fig. ri2], U( c »r(l of (liiiriuil variations of light and of temperature in suininer.

dotted record near the base shows tliat the resistance
remained practically constant, inspite of the variation of the
temperature.

An important point arises as regards the diurnal varia-
tion of liglit and of temperature, and determination of their
periods of maximum and minimum. For this purpose
records of (hiniiil variatioiT^ of temperature and of light were
taken on the same day in summer with the thermograph
and the radiojinmli. The tw.) curves are gfiven in Figure 3"21.

SELF-RECORDING RADIOGRAPH 833

It will be seen that while the maximum intensity of light
is at 12 noon, the thermal maximum is at about 2 p.m. The
thermal noon is thus two hours later than the light-noon.
Light disappears at night from 6 p.m. to 6 a.m., that is to
say, the period of minimum is prolonged for 12 hours. But
the fall of temperature is gradual, and the minimum is
attained at about 5 a.m. which is the thermal dawn. The
characteristic variations of these two important factors
should be borne in mind, since the diurnal movements of
plants are modified by the algebraical summation of the
effects of light and of temperature.

It is sometimes desirable to carry out researches during
a period when the intensity of light remains approximately
constant. This period is found to be between 11 a.m. and
1 P.M. for the variation is only + 5 per cen:. of the mean.

The record given of the diurnal variation of light is true
of days when the sky is clear. But the passage of cloud
causes change in the intensity which is accurately recorded
by the Eadiograph. A record of such irregular variation in
a stormv dav is given in the lower record of Figure 320.

SUMMARY.

The Eadiograph gives a record of the diurnal variation
of light. On a clear day in January, the intensity was found
to increase rapidly from 6 a.m. to 12 noon, when it reached
its maximum. Light began to decline slowly up to
5 p.m., the decline being less rapid than the rise at the
forenoon. The fall of intensity was extremely rapid after
5 p.m.

Any fluctuation of light due to passage of a cloud is
accurately recorded by the Eadiograph.

834- LIFE IMOVEMENTS IN PLANTS

The fall of intensity of light is abrupt after 5 p.m., and
the minimum persists from 6 p.m. to 6 a.m. In contrast
to this, is the periodic variation of temperature which
attains its maximum at 2 p.m. and its minimum at 5 a.m.
The former may be regarded as the thermal noon, and the
latter as the thermal dawn.

LXXIII.— ON A VEGETABLE PHOTO-ELECTKIC

CELL.

By Sir J. C. Bose,

Assisted by

GURUPRASANNA DaS, L. M. S.

Vegetable tissues have been shown to exhibit an
excitatory reaction under the stimulus of hght, the response
being by contraction (p. 208) and by diminution of resist-
ance (p. 816). The corresponding electromotive response
under excitatory action of light would be b}- an induced
change of galvanometric negativity. This normal electric
response under the stimulus of light has been demonstrated -
in my work on Comparative Electro-physiology.

Some observers have, however, obtained in green leaves
a response of galvanometric positivity. This anomalous
result would seem to indicate that the response to light is
of an opposite sign to that induced by other modes of
stimulation. It would, however, be shown that the normal
response to light is by induced galvanometric negativity,
the positive response being brought about under certain
specific conditions.

NORMAL RESPONSE TO LIGHT,

For obtaining the normal response, we take a vigorous

leaf and pin it on a paraffined block of wood. Two pieces

of thin muslin in connection with non-
Experiment .336 , . . . ^

polarisnig electrodes are spread over two

a,reas of the leaf A and B ; when these pieces of muslin are

835

836 LIFE MOVEMENTS IN PLANTS

moistened with normal saline, they become practically
transparent. When light from an arc lamp is thrown on A^
that area becomes galvanometrically negative and the
direction of the responsive current is in the direction of
GAB. Light thrown on B (A being shaded) causes a
response in the opposite direction, (left illustration Fig.
3-2-2).

The fact, that the electromotive response under light is
the same as that under any other form of stimulus such as
mechanical, is demonstrated as follows. The moist piece
of cloth on A is rubbed against the surface of the leaf by
means of a glass rod; or the leaf may be struck with a glass
hammer. In both these cases, A becomes galvanometric-
ally negative, the direction of the current of response being
the same as when A is stimulated by light.

Having given a simple demonstration of the funda-
mental reaction, w^e shall now describe the photo-electric
cell made of two pieces of leaf. In the experiment described
above, the resistance of the circuit is very great, first on
account of the high resistance of the two non-polnrisable
electrodes, and secondly because of the resistance offered by
the leaf. The non-polarisable electrode, moreover, is a-
source of much trouble ; an attempt was therefore made to
discard it, and employ means for diminishing the resistance
of the circuit. For the following experiments we employ the
leaf of Musa sapientum which are divided into two long-
itudinal halves by a slit along the thick midrib. Two pieces
of leaves are thus obtained about 10x10 cm. which are
hung parallel and separated from each other in a rectan-
gular glass vessel filled with normal saline ; the distance
between the two leaves is 3 cm. Two gold wires are thrust
through the length of the two divided midribs ; they serve as
the external electrodes of the photo-voltaic cell, leading to
the galvanometer G. The glass trough is placed inside a
rectangular wooden chamber with two hinged doors on

VEGETABLE PHOTO-ELECTRIC CELL

837

opposite sides, by which the leaf A or B could be alternately
exposed to light (Fig. 3"2'2). When the door.-; are closed, A
and B are in darkness ; they are practically iso-electric, there
being no current in the galvanometer. But exposure of A
to light gives rise to a difference of potential between A
and B, A becoming galvanometrically negative, the result-
ing deflection being in one direction. Exposure of B gives
rise to a responsive deflection in the opposite direction. The
two leaves serve as the two plates in a voltaic cell ; but
unlike ordinary voltaic cell with elements of different metals.

Fig. 322. Diagrammatic representation of a vegetable photo-electric cell.

The first illustration shows electric connections with two portions of
the leaf A, B, by non-polarisable electrodes The second and third illus-
trate (side and front views) of the photo- voltaic cell made of two half-leaves.

the two plates of the vegetable cell are made of two halves
of the same leaf, the electromotive force being generated by
the excitatory action of light on one of the two half leaves.
The advantages of this method of obtaining electromotive
response are : (1) that the troublesome employment of the
non-polarisable electrodes with their high resistance is
dispensed with; (2) that the area of the surface of the leaf
exposed to light is considerably increased ; (3) that the
electric resistance of the circuit is greatly decreased, since
the interposed resistance is that of normal saline about
3 cm. thick with a broad section of 100 square cm. ; and

^'■iS LIFE MOVEMENTS IN PLANTS

<4) that alternate and opposite responses may be obtained
by successive exposures of tlie two leaf-plates to the parallel
beam of an arc lamp, this being easily secured by turning the
rectangular plant chamber round a revolving base.

RESPONSE OF THE LEAF TO LIGHT.

The photo-voltaic cell thus constructed is stimulated by

light from an arc lamp which passes through a trough of

alum solution for absorption of the heat rays.

Exp.TiiiitMit ;};^7 Q • 1 r 1A

successive exposures are made tor 10
seconds and records obtained on a moving photographic
plate. The normal responses are uniform, exhibiting in-
duced galvanometric negativity as seen in the up-curves. On
the cessation of light there is a complete recovery ; in fact,
the recovery shows an overshooting towards galvanometric
positivity from which it returns almost to the original zero
position before stiiinilation. There is a curious resemblance
of this after-effect of electromotive variation to that of
resistivity variation (see Fig. 308) ; both the records indicate
that stimulus often gives rise to dual effects, a negative
variation or D-effect followed by a positive variation or the
the A-effect.

POSITIVE RESPONSE TO LIGHT.

We shall next consider the anomalous result wiiich
■sometimes occurs, namely, the positive response to light.
It has been shown (p. 810) that a positive lesponse occurs
under a stimulus below the critical intensity, and that this
critical point is low in highly excitable tissues, whereas it
is relatively high in others in condition of depressed
excitability. It has been further shown (p. 7.')7) that while
the excitability is relatively high at a certain age of the
specimen, it is lowered when the tissue is either very young
or very old. We may, therefore, expect that the same
stinmlus which evokes a negative response in a vigorous
middle-aged leaf of Mtisa, would give rise to a positive

vF-ci-yrAiii,!-: riKvro-Ei^RcTTnc cktj, S;3i)

response in a very yoimji leaf or in a leaf v.hich is becoming
yellow with age.

The above anticipations have been found verified in the
foUowiu"^- exiH'riiiients. In l^'iginv -VM is seen the positive
rt>sj)onse of a xt-ry young' leaf. Figure 3'25
shows similar positive response given by a
very old leaf. There is an additional element which tends

Experiment Hr^S

FK;. jzj fig j24 KIG. 325

Fig. 323. Normal oleotromotive response in a vigorous specimen.
Note the transient positive after-effect.

Figs. 324 and 325. Abnormal positive responi-e in a very young and in a
very old specimen.

to produce a positive res])onse of which reference will be

presently made.

It has been shown that the reaction under light, is

within limits, proportional to the quantity of light, that is

to say, on the intensity multiplied by
Experiment 339 , . ,.,-,/ ..,-x t- • ^i.

duration of light (p. 34o). Keeping the

intensity coni^tant, we obtain responses to increasing" dura-

SU) LIFF. MOVK:\rF\TS IN PLANTS

tions of liglit; of 5 seconds. Id seconds, and lo seconds. T}ie
responses are seen to nnder^^o an iiicii^ase with the increased
duration of exposure (Figure 32G). But this increase does
not go on indefinitely, for the conliiuious action of hght
causes a maximum negative response beyond which a dechne
sets in. There must, therefore, be ?n opj)osing element
which tends to neutralise the normal excitatory D-effect.

Fiii'. Hiirt. Kffects (if iiicrciisi!ij( durations of oxposure
of ."), 10, and 15 seconds.

The existance of this opposing A-reaction has already been
seen in the transient after effect in Figure 323. We have
already seen that stimulus in general, induces both the I )-
and A-effects ; in excitable sptnimens the D-effect is predo-
minant and therefore, masks the A-effect ; this positive A-
eft'ect is, however, exhibited under feeble stin \dus or e^en as
an after-effect of strong stimulation.

VKGETAIil-K PHoTO-KLKCTlilC CKF.L

,S4

There are aj^aiii certain conditions which are specially
favourable for the exhibition of the A-effect. When the
^reen leaf has an abundant sujij)ly of chlorophjdl, the photo-
synthetic process of building up becomes specially marked.
1 have tlius obtained under tlu> action of lipid, a positive

Fiir. '•^2'l. Aftei'-efl'ect of liylit. I'lio iiia.xiuiuni iioirativc is i-c\erso(l
sinii attains a balance iti the liorizontal portion of tlie curve Sroppafi'e
of liylit causes the uniiiiiskiiiff of the iievative followed bv recovcrv.

response with the green leaf of Luctuca sativa in wliicli
chlorophyll is presenr, in such a j^reat abundance.

The fact that positive response is associated with
assimilation is proved by my recent experiments on photo-
electric response of water plants. The photosynthesis
under hght is liere independently demonstrated by ])r()fuse
evolution of oxvjaen. These water plants exhibit marked
positive electric response during strong illumination, the
response disappearing on the cessation of light.

NI2 LIFE MOVEMKNTS IN I'l.ANTS

EFFECT OF CONTINUED ACTION OF LIGHT.

The positive element in the response may be indirectly
ilomonstrated even in the normal Mnsa leaf. In Figure 327
is seen the elTeot of continnoiis action of light
wliitJi at first exhibits the predominant
negative response attaininp' a maxinnnn ; the positive
element now begins to increase with the duration of light ;
at a certain stage, the two elements, D and A, balance
each other ilie residting response being boiizontal. On
stoppage of light, the antagonistic A element ceases to be
active, while D appears to be persistent. The result is a
sudden unmasking of the negative, held in balance during
exposure to light. A negative response with subsequent
recoverv thus occurs on the cessation of light (Fig. 237).

SUMMARY.

A photo-electric cell is constructed of two half-leaves of
Musa, supported parallel, in a trough filled with normal
saline. The two halves act as two metallic i)lates of a
voltaic cell. The resistance of the circuit is thus greatly
reduced.

An electromotive force is generated by exposure to light,
the stimulated leaf becoming galvanometrically negative;
there is a recovery on the cessation of light.

In vigorous leaves, increasing duration of light gives
rise to increasing negative response which tends to reach a
limit.

The excitability of a very young or a very old leaf is
below par; the response in such cases is by galvanometric
positivity.

VEGETABLK PHOTO-KLFX'TRIC CELL 843

On ac-couiit of pliotosyntliesis there is a positive element
in the response which is often masked by the predominant
negative. The positive is often found as an after-effect in
the normal negative response. Under continued action of
light the negative is opposed by the increasing positive,
bringing about a condition of balance. On the stoppage of
light the masked D-effect exhibits itself as a short-lived
negative response.

]jXXi\'.— (ii>:.\i:K.\i. iM-:\ii-:w

OF

VOI.UMKS I I'O I\'.

'!'li(> iiioveiiuMits of plant of.^ans iiiulci- the manifold and
(■Iiaii,L:iii<^' forces of tlic cm iromnciit are exti"(Mneh' varied
and coni[)licate(l. Tlic most important of these are tlie
effects of variation of tempei'ature, of the stimuli of contact,
of ^'i-avity and of li^lit. Tlu^ effcM-ts of tliese diverse agencies
ai'e not aK\ays concoi-danl . but often contradictory. The
same stinudus is found. moi'eoNcr. to prcxhice sometimes
one i^lfect, and at other times iirecisely the opj)osite. It has
thus appeared almost hopeless to discover an underlying
unity in phenomena so extremely diverse. A tendency has
thus arisen towai'ds the hcdief that it was not any definite
pliysiolo^ical reaction, hut the in(n\ iduahty of the plant
that determined the choice oi' mo\euient for its ultimate
advantage. Teleological argmnent of this character con-
fuses the real issue, and diverts attention from the discovery
of tile fundamental physiological mechanism. Terms and
phrases have been employed for difl'erent mo\ements, sncli
as positive heliotropism when the organ turns towards,
negative heliotropism when it moves away, and dia-helio-
tropism w hen it places itself at right angles to the direction of
light. Sinnlarly the terms j)ositive and negative geotropism
have been used to denote the mov<'ment towards or away
from the earth. These terms olfei' no real e\j)lanation of

M I

GENKHAL lU^lEW 845

the phenomena, and their use, as pointed by Bayliss, have
proved to be "" mischievous, leading to the behef that new
knowledge has been obtained when a phenomenon is des-
c-ribed b}- a name deilNt'd Irom the classical tongue instead
of in English.""

The advance of physiology of plant-movements has been
delayed, mainly from the lack of definite knowledge in
regard to (1) tlie fundamental reaction induced by different
forms of stimuU, CJt the modification of tlie effect brought
about by changes in the tonic condition of the tissue, (3) the
different effects of feeble, moderate, and strong stimuli, and
(4) the variation of effect which arises from tlie direct and
indirect applications of stimulus.

As regarils the first, it has been thought that the effects
of different stimuli are specificallv different. In reality
there is no such difference, for the investigations described
in these volmnes show that all stinmli induce similar exci-
tatory reaction by contraction. Perception of stimulus and
the consequent reaction arises from the disturbance of the
sensitive protoi)lasm. Though certain anatomical struc-
tures, such as tactile hairs and others facilitate the percep-
tion of a particular form of stimulus by causing deformation
of the sensitive protoplasm in an affective manner, yet all
forms of stimuli are found to induce similar reactions, as
exhibited by contraction or by the concomitant response of
galvanometric negativity.

The second i)oint relates to the modifying influence of
tonic condition ; it has been shown that while in the normal
condition of the tissue, the response is by contraction, in a
sub-tonic condition it undergoes a reversal of sign, the
response bemg by expansion.

In regard to the effects induced by varying intensities of
stimulus, it has been found that a feeble stimulus induces
an expansive reaction, in contrast with the contractile effect

84t) LIFE MOVEMKNTS IN PLANTS

of a moderate stimulus. Strong' stimulus, a^ain has been
shown to give rise to a multi{)le series of responses.

And finally, the existence of a very important
factor liad not previously been suspected, namely,
the differing effects induced by change in the point of
application of stimulus. It has been shown that while
direct stimulus induces a diminution of turgor and contrac-
tion, indirect stimulus causes the opposite effect of increase
of turgor and expansion (p. 130). The explanation of this
is found in the fact that owing to the semi-conducting
nature of the vegetable tissue, the excitatory impulse from
a distance undergoes rapid diminution, and becomes
minimal when it reaches the responding organ ; but
minimal stimulus is shown to induce an effect which is of
opposite sign to that of normal intensity (p. 80U). In the
second place, the local coiiti'action caused by stinudus
causes an expulsion of fluid giving rise to a hydraulic wave
wdiich forces water into the res{)onding organ at a distance
and causes an expansion.

The following generalisations have been experimentally
established : —

I. Under normal conditions , (dl forms of stimuli of
viodcrate intensity (jive rise to negative responses, seen
exliibited by contraction, diminution of turijor, fall of leaf,
electromotive change of galvanometric negativity and a
diminution of electric resistance.

II. Feeble stimuli give rise to responses ichich arc
positive, i.e., of opposite sign to the normal negative.

III. In the sub-tonic condition of a tissue the response
under moderate sti}nulus is positive.

JV. Strong stimuli give rise to multiple responses.

\'. All forms of Direct Stimuli i)iducc contraction:
hidircct Stitnuli, o)t the other hand, (-(nise expansion.

Tlie diverse movements of y)lants are explained on the
principle broadlv stated above. Some of the more import-

GENERAL Kl'VIKW 847

ant investigations ik'sciilxHl in the lour voltnnes may now be
classified as follows.

1. Similarity of iTspons" in pulvinatrd, ,i,'r(nvin^\ and non-
growing organs.

(a) Response of Mimosd.

(h) Diurnal variation of moto-excitability.

(r) Response of ordinary plants.

{(l) Response of growing organs.

2. Different methods of detection of negative and positive

responses.

(a) Mechanical response.

(6) Electromotive response.

(c) Response by variation of electric resistance.

(f/) Permeability variation under stimulus.

3. Identical excitatory reaction under different modes of
stimulation.

4. Positive response under feeble stimulus.

5. Modification of response in sub-tonic tissues.

G. Opposite effects of direct and indirect stimulation.

7. Multiple response under strong stimulus, and the con-
tinuity of multiple and autonomous responses.

8. Autonomous respon.sc.. and tbe movement of growth.

9. Effect of anaesthetics on various responses.

{'i) Carbon dioxide on electric response, on growth, and on

geotropic response.
(h) Ether vapour on electric response, on growth, and on

geotropic r.sponse.
(c) Chloroform vapour on Desmoclmm pulsation, on growth,

on geotropic response, and on electric response.

10. Death-spasm in plarts and the transmission of death-
excitation.

11. Nervous impulse in plants.

12. The Nervous and the Hydraulic reflex.

13. Tropic movements under unilateral stimulus.
1 f. Mechanotropism.

''^-l''^ I. IKK MOVKMKNTS IN IM.ANTS

1 •">. I'liot'itropisiii.
(o) Quantitative relation.
(fi) Negative phototropism.
(r) Effects of different rays of the spectrum.
(«■/) The complete phototiopic curve.
(t) Phototropic torsion.

1(). Dia-hcliotropic adjustiiu'iit of leaves under trans-
mitted excitation.

17. JMiotonastie curvatures.

IS. Xiglit and day movements of plants.

(<i) Thernionastic movements.

'Jt) Thermo-geotropism.

(r) The .Self-recording Hadiogi'ai)h.

((/) Movement due to alteration of light aiul daikness.

(') Diurnal movement of Milliard.
1*1. ( ieotropism.
(<i) Mechanical respi)nse.
(//) Electric res|)onse.
(<■) Exjilaiiation of opposite reactions at upp(>r and lower

sides.
{(I) (ieotrojjic excitations at vaiious angles.
{<) Effect of narcotics.
(/) Effect of variation of temperatui'e.
(ij) Localisation of geo pei'ceptive layer.
{h) Dia-geoti'oi)ism of doisi-ventral oi-gans.

(/) Geoti-opism of roots.

The iiiaiii resulls of these ciKpiiiies may now he hriefly
untliiicd under the ahoNe JK^adinjus.

i!i-:si'()Nsi': IN n i.\ IN ATI' I). (,i;()\vin(;, and

N()N-(;i;()\VIN(i OKO.VNS.

}f((h(nii<(iJ rrsjxiH.sc of Miniosd. — Both ihe upper and
the lower halves of the ()ulvinu.s are sensitive, hut the lower
lialf is ahoiit 80 times more excital)le tlian the ujij^er.
DitVii.se stimulation Induces responsiv(^ htli hy the f^reater
contraction of the lower half. Foi" a Ion;.! tim(> it has
heen as-.ume(l that the expansive hiree of upper half of the

CHNKIJAL KKVIKW 84{>

pulviiuis and the weij^lit of the leaf are important factors in
the resiH)iisive fall of the leaf. Experiments carried out
after ciittinii" off the siih-petioles, and the amputation of the
upper or the lower half of the [)ul\iiuis show that tlie
responsive movement is maiidy i\ue to the active force of
contraction exerted by the lower half of the pulvimis (]).
85).

l)iitr)uil i'<iri(iti(i)t of )ii<)to-c.rcif<ibilit!i of Miiiiofid. —
The m()to-excital)ility of Miniosti undergoes a diurnal
variation. The plant is almost insensitive in the morning;
the excitability is gradually increased to a maxinnna at
1 P.i\[., which remains constant for several houi's. A con-
tinuous fall of excitability begins in the evening, the minimum
being reached in the morning. This variation of excita-
bility is j)rimarily due to the diurnal change of temperature,
and in a minor degree to variation of light (p. 71).

Hcsponsc (if urdiiKinj plavts. — The distinction between
sensitive and ordinary plants is arbitrary, since sensitiveness
can be demonstrated throughout plant life. Thus radial
organs exhibit a shortening of length under stimulus. The
characteristics of the response of ordinary plants are t:he
same as those of the sensitive Mituosa (p. 37). As the
different flanks of the radial organs are equally excitable,
there is no lateral movement under dift'use stimulus. In a
radial tendril a pliysiological anisotropy is, however, in-
duced by the action of stimulus on one side of the organ.
In such £ curved tendril, the concave side is less excitable
than the convex. Diffuse stimulus tends to straighten the
curved tendril by greater contraction of the convex side (p.
41). Under geotropic action, a radial organ is rendered
temporarily anisotropic ; diffuse stimulus then causes a
responsive movement by which the curved organ becomes
straightened. The temporary anisotropy may be neutralised
and reversed by inverting the organ, the response under-
going corresponding reversal (j). 681).

^r>0 ]AVh] MOVKMKNTS IN ]'[,ANTS

Rcspo)isc of (iroiciiKj oiyidtts. — By iiiciiiis of the High
Magnification Crescograpii the normal rate of growth and
its iiuluced variation are (let(M mined in the course of a few
seconds. The magnificiition thus obtained may be as much
ten thousand times. \\liiU> the Magnetic Crescograph can
give an amphfication up to ten. milHon times, tluis enabhng us
to observe and measure the rate of growth, and its slightest
variation. The effect of stimulus is found to induce an
incipient contraction, exhibited by a diminution of the rate
of growth: this I'ctardation increases \\ith tlie increasing
intensity of stimuhis, ciihninating even in an actual shorten-
ing of the organ (p. 1 ()(')•.

The sensitiveness of these methods for detection of
induced variation of growth can l)e yet further increased by
the use of the Balanced Crescograph. In this the move-
ment of growth upwartls is exactly compensated by an equal
movement of the plant downwards, with the result that the
record remains horizontal. The effect of an external agent
is inmiediately detected by the upsetting of the balance; up-
record representing acceleration above normal, and down
record, the opposite effect of depression. The sensitiveness
of the method of Balance is so great as to enable us to detect
the retardation of growth induced b}^ a single flash of light
lasting for about- a hundred thousandth of a second (pp. 263,
3-2o).

DIFFERENT METHODS OF DETECTION OF NEGATIVE
AND POSITFVK RESPONSES.

It is convenient, and often necessary, to have at our
■disposal independent methods of detection of excitatory
reaction in plant tissues. I have shown elsewhere* that
every plant, and every oruan of every plant exhibits exci-
tatory response by an induced change of galvanometric
* Responses in the Living and Non-I^iving, (1902).

C.KNRUAL KFVIKW 851

negativity. That the electromotive response is but a
(hffereiit ex[)iession of protoplasmic excitation has been
xliown by obtaining" a simultaneous record of niechanical and
electric-al res[H)nse of Miniosd ([). Hh]). AnotluM- method
has also been described by which the excitatory reaction is
detected and recorded by the iiiduc-ed diminution of the
electric resistance of the tissue (pp. 7".)6, bOo). The Quadrant
Method devised for obtaining" response by change of electric
resistance is found to be extremely sensitive.

NEGATIVE ANT) POSITIVE RESPONSES.

There are two fundamental reactions distinguished as
ncijatire and positive which underlie all physiological varia-
tion. The outward manifestations of the excitatory
negative are, (a) diminution of turgor, (b) contraction, (c)
fall of motile leaf, (d) diminution of the rate of growth, (e)
electromotive change of gaivanometric negativity, and (f)
diminution of the electric resistance. While the positive
reaction is associated with, (a) increase of turgor, (b) expan-
sion, (c) erectile movement of the motile leaf, (d) increase of
the rate of growth, (e) electromotive change of gaivanometric
positivity, and if> increase cf electrical resistance. The
excitatory effect is seen in response to moderate stimulus
of all tissues in normal vigorous condition. The positive
effect is demonstrated by irrigation of the plant, with the
resulting" ascent of sap by which the turgor of tissue is in-
creased. The same effect may also be produced by applica-
tion of hydrostatic pressure. In another aspect, th? negative
and the positive responses are associated respectively with
the breakdown, D-change, and the building" up, A-change.
Stimulus induces both D- and A-changes, the separate
existence of which has been demonstrated.

The closest parallelism has been established between
the results obtained with mechanical and electrical responses

8o2 I,1FK MOVI'IMKNTS IN PLANTS

of non-iii'owin;^" or^^aiis iiiuUm- stiiiiiilus. and tlie responsive
variation ol' growth . ( 'iiciimstanccs which give rise to
negative mechanical and eledrical responses also give rise to
negative Nariation oi- retardation of th(^ rate of growtli.
Other circumstances which cause j)ositi\'e mechanical and
electric responses hring aho'it positive \ariation or enhanct'-
nient of the rate of growth. The physiological machinery
is alike in ])mI\ inaliMl , non-[iid\ inated, in growing, and in
non-growing oi'gans.

Tiise of t(Mnp(Mat nre. within hunts, induces an ex])ansion,
and an acceleration of the I'ate of growth. The reaction
induced hy a rise of tempei'atui'e is often antagonistic to that
induced hy stinudus.

M (■(■liiiiilcal response. — The lU'gative response is seen in
the fall of the MlnidSd leaf ind in the retardation oi the rate
of growth (p. ]'.)7t. That the positive response due to the
enhancement of turgoi" is shown hy the erectile movement
of the leaf of Miiiiosd (j). .■{'.)>. and hy the eidiancement of the
rate of growth (j). IDO).

FAeciroiiiofire resjxinse. — The normal excitatory
response of galvanometric negativity has heen sh.own to
occur under mechanical stimulus (p. 88G), under electric
stimulus (p. 744) and imder stinndus of light (p. 838).

1 have in my later experiments found that an enhance-
ment of turgor gives rise to an electromotive change of
galvanometric positivity.

Both the D- and A-changes occur under the action of
stinndus; since the excitatory D-reaction is, imder normal
conditions, relatively predominant the negative' electric
variations masks the positive. Tlie ])()sitive A-change may,
however, he munasked on the cessation of stinndus, when ii
is exhihited as a short-lived positive after-effect (p. 838).
Under continuous stinmlaticn by light the increasing A-
eflfect neutralises the negative; on the stoppage of Hght the
balanced D-effect \>: unmasked (p. 84-2) wit>h re.sulting

GENERAL REVIEW 858

negative response. 1 have recently succeeded in ()l)tainin^'
the pure assiniilatory response of galvanonietric positivitv
under the action of hght in actively jihotosynthetic water
plants like Ihjdrilld rcrticilldtd. Here active assimilation is
simultaneously exhibited in two different ways : (1) by
evolution of oxygen, and (-2) by the positive electric variation.

Response by z'ariation of cleetric resistanee. — The
excitatory negative reaction has been demonstrated l)y the
induced diminution of electric resistance under mechanical
stinndus (p. 801), under electric stimulus (p. 808), and under
the stinudus of light (p. 816). In the Quadrant Method
the two opposite quadrants are shaded, and illumination of
the unshaded quadrants upsets the previously balanced
resistance. The sensitiveness of the method is so great that
it detects and records the diminution of resistance induced
by the almost instantaneous flash of light given by a single
electric spark (p. 817 1.

Contraction and pcrmeahUity variation. — The excita-
tory fall of the leaf of Mimosa is due to the expulsion of the
sap from the excited cells in the pulvinus. This may be due
to an active contraction or to an increase of permeability of
the protoplasmic lining of :he cell. According to Schafer,
the contraction of a muscle is brought about by a transfer
and redistribution of fluid material ; the contraction of the
pulvinus of Mi))wsa is also due to the transfer of fluids. All
movements of living organism, whether animal or plant,
may be said to be effected by essentially the same means,
i.e., by the contractile protoplasm, of which the highly
specialised form is seen in the muscular tissue of the animal.
It has been shown that a simple theory of permeability
variation is not sufficient for a full explanation of the observed
phenomena (p. 820). These rather point to the existence
of two definite protoplasmic reactions, which may be des-
cribed as the A- and the D-effects.

854 LIKK MOVK.M'A'TS IN I'l-A'NTS

IDENTICAI. HXCI I'A roHY IJKACTION INDl'.K DIFFKHENT ]\10DES
OK STIMI'LATION.

Among tlu> dilVci-'Mit tonus of stiimili are; contiu-t and
friction, [)rick and wound, induction ch^'tric shock or sliock
of condenser discharge, the ' make ' of an electric current
at the kathode, tlie action of certain chemical agents, the
action of the rays of hght from the more refrangible portions
of the spectrum, the infra-red thermal radiation, tlie electric
radiation, and the action of gravity.

Mechanical and electrical stiimdi alike cause a fall of
the leaf of Mimosa, a diminution of the rate of growth
(p. •I'-V.)), an electromotive change of galvanometric negati-
vity (p. 744), and a dimimition of electrical resistance of
the tissue (p. 808). Stimulus of light causes the fall of
Mimosa leaf (j). '245), reta.-dation of the rat(^ of gnnvth
p. •206) ; positive troi)ic curvature in growing organs (p. 318),
electric variation of galvanometric negativity (p. 838), and
diminution of electric resistance fp. 816).

Thermal radiation by dinnnishing the rate o." growth
induces a positive tropic curvature in growing organs.

Electric radiation of wireless stimulation of moderate
intensity induces a retardation of growth (p. 4*2-2) and an
electric variation of galvanometric negativity.

POSITIVE RESPONSE UNDER FEEBLE STIMULUS.

This is seen in the erectile response of Mimosa, in the
enhancement of the rate of growth (p. 224), in the response
of galvanometric positivity, and in the response of the
increase of electric resistance of the tissue (p. 809)

MODIFICATION OF RESPONSE IN SUR-TONIC TISSUES.

The normal negative response undergoes a reversal in
sub-tonic sj)ecin)ens seen in positiw meclianical response, in

OENERAL KEVIKW g55

an acceleration of the rate of nrowth (p. 221). Continuous
stimulation converts the abnormal positive into normal
negative response. The abnormal response fin dr. expla-
nation in the fact that stimulus give rise simul-
taneously to two reactions, the positive associated
with an 'up' or A-change and the excitatory
negative, associated with the 'down" or D-chanc^e
In excitable condition of the tissue, the negative
D-change is predominant ; conversely, the positive A-change
is very pronounced in a tissue whose tonic condition is belo''^
par. The A-change enhances the potential energy of the
system. Hence successive stimulations, by enhancing the
functional activity of a sub-tonic tissue, convert the
abnormal positive into normal negative response.

OPPOSITE EFFECTS OF DIRECT AND INDIRECT STIMULATION.

Every stimulus is shown to give rise to two separate and
distinct impulses :-the positive, which is independent of
the conductivity of the tissue for its transmission, and the
excitatory negative which is dependent on the conducting
power. The former is transmitted quickly ; the latter, being
a phenomenon of conduction of protoplasmic change, is
conducted slowly. The positive impulse gives rise to
expansion, positive electric response, and an acceleration of
the rate of growth. The excitatory negative gives rise to
contraction, negative electric response, and to retardation
of the rate of growth. The negative reaction, is more
mtense than the positive. When the intervening distance
between the point of application of stimulus and the respond-
ing organ is sufficiently great, the negative impulse lags
behind the positive ; the response is then diphasic, positive
followed by negative. Reduction of the intervening
distance causes a masking of the positive by the predomt
inant negative.

R

856 l.ll-l', MOVKMKNTS IN PLANTS

A negative res[)oiise lias Ixhmi shown to take place
under ;i difect stiiiiiilatioii of the responding organ. When
the stiitiiiliition is applied at a sufficient distance, the exci-
tatory inii)ulse hecouies weakened to the point of extinction ;
the response is then positive as seen in the erectile response
of various motile U>aves and leaflets (p. 188), and in tlic
enhanced rate of growth in growing organs (p. '214).

MUl/nriiK RKSPONSE UNDER STRONG STIMULUS, AND THE
CONTINl ITY BETWEEN MnUTIPLE AND AUTONOMOUS RESPONSE.

When a plant organ is subjected to a strong stimulus,
it exhibits a series of multiple responses. This is seen in
the multiple mechanical response (p. 784), in multiple
electromotive response (p. 744) and in nniltiple response of
resistivity variation (p. 811). These undtiple responses
are induced by various modes of strong stinnilation, such as
induction shock, constant electric current, strong light,
thermal shock, and mechanical excitation. In such cases
the excess of stimulus is, as it were, held latent as may be
observed in the subsequent multiple responses.

These recurrent responses under strong stimulus are
strikingly demonstrated by the leaflets of Biophytinn^ the
characteristics of which are like those of the cardiac tissue
of the animal. Both are characterised by a long refractory
period and response on " all or none " principle. In both,
a single moderate stinudus gives rise to a single response;
and a strong stimulus causes a multiple series of responses.

There is no strict line of demarcation between the
phenomenon of multiple response as examplified by the
leaflets of lliopliytnw and that of autonomous response as
exhibited by the leaflets of Dcsmodium. Under very
favourable conditions of absorption of energy from without,
an ordinarily responding plant like Biophtjtvm becomes con-
verted into an " automatically " ])ulsating plant like

GKNMKAL KI'A IF.W 857

DesmoditoH. Conversely, under unfavourable conditions, —
i.e., when the sum total of its energj' is below par — the auto-
matically responding Dcsmodiiini becomes reduced to an
ordinarily responding plant like Biophytum. Its leaflets
then come to a standstill. Their pulsations may then be
renewed by external stimulus, the persistence of which is
found to depend on the intensity and duration of the stimulus
absorbed.*

AUTONOMOUS JJESPONSP: AND THE MOVEMENT OF GROWTH.

The pulsating movement of the lateral leaflet of
Desmodium is a striking example of the spontaneous activity
of plant tissues. The general characteristics of a pulsating
tissue are : (1) the periodic increase and diminution of
turgor, ('2) the dependence of activity on internal hydrostatic
pressure, — a diminution causing an arrest, and an
increase bringing about a renewal of pulsation, (3) the
storage of external stimulus in the maintenance of
rhythmic activity, — a run-k.wn of absorbed energy being
followed by an arrest and a renewal of arrested activity
after the application of fresh stinudus ; and finally, (4) the
modifying influence of temperature, seen in the arrest of
pulsations at a critical temperature, and in the maximum
activity at an optimum temperature.!

All the above characteristics are found in the auton-
omous activity of growth, wdiich is also found to exhibit
pulsations (p. 169). Grow^th is arrested under diminished
internal hydrostatic pressure produced artificially or under
drought ; it is enhanced by increased internal pressure after
irrigation (p. 189). Growth arrested under condition of
sub-tonicity becomes revived by the action of stimulus. The

* Bose— Irritability of Plants, p. 289.
jlhid, p. 291.

^58 LIFK MOVKMKNTS IN PLANTS

t-1-itical teni|)ci;itur(' \\)V llic aiTcst of Lirowlli in many tro-
pical plants is about -I-I^C. i|>. ITTi, the opliimini tempera-
ture for niaxinnun rate hi'iii;^ about 34°C.

In my lortiu-omin^' work on tlie " Ascent of Sap " it is
shown that the ascent is i)rou;^ht about by the ])nlsaTory
activity of the cells of the internal cortex which extends
throughont the length of the ])lant, the movement of the sap
being essentially due to the pumping action. Furthermore,
that the rate of ascent is (hnnnished by the (bminution of
the int(M-nal hydrostatic |>ressure ; that the arrested ascent
ill a plant in a condition of sub-tonicity is revived by
the action of external stimidus; that the ascent in many
tropical plants is arrested at a similar critical temperature ;
and that the transpiration from leaves exhibits a maximnm
at the similar optimum tem[)erature, of 33° or thereabouts.

THK EFFECT OI' ANAESTHETICS.

Carbon (Hoxide may l)e taken as a mild anaesthetic,
ether vapoiu- l)eing stronger in its action. The effect of
chloroform vapour is nuMe ii>tense and liable to produce fatal
results. The action of anaesthetics is modified by the
strength of the dose and the dtu'ation of application. Under
the continued action of an anaesthetic different reactions are
generally found to occur at three different stages.

C'drhoii (li(i.ri(lc.— T\\c prchminary effect of tliis gas is
an increase of acti\ ity follow ( d by a decline.

This is seen in the preliminary enhanced response by
resistivitv variation under the stimulus of light; continued
action of the gas causes a depression in the response
(p. slO). Similar results are seen in response under electric
stinndatioii (p. Sl-2).

In growing organs the preliminary effect of this gas is
an enhancement of the rale followed by a retardation
(p. 305). Continued action of this gas may ev(Mi cause an

(.KNKi;\i, i;i:viF.\v {559

active tontnutioii which peisists ihiiing the api)lication of
the jjHs, tlie norma! growth being restored after renewal of
fresh air (p. fiHS*.

Geotropic- response is brought about by ditlerential
growth induced at the upper and lower sides of the organ.
The acceleration of growth t-aused by COo at the first stage
gives rise to an enhancement of geotropic response. But
<?ontinued action of this gas causing contraction brings about
a reversal of the normal geotropic response from an up- to a
down-curvature. This explains the apparent reversal of
normal geotropic response under carbonic acid gas (p. 644).

Effect of ether vajtoiir. — Dilute vapour causes an
increase of activity seen in the enhancement of electric
response (p. 81"2), in the initiation or enhancement of
growth, and in inducing a great increase in the rate of
geotropic response (p. 663).

Effect of vapour of chloroform . — The application of this
anaesthetic gives rise to different effects at three different
stages. The immediate effect at the first stage is an
•enhancement of activity; at the second stage, there is an
arrest : and at the third stage, there occurs a spasmodic death-
contraction. The effects of these three stages are well
exhibited by changes induced in the rate of growth. An
arrested growth becomes revived or the normal rate becomes
enhanced at the first stage. At the second stage, growth
becomes arrested: and finally, at the third stage there is
produced a contractile death-spasm.

In the geotropic response the immediate effect of chloro-
form vapour is a great enhancement followed by an arrest
under continued action of the narcotic (p. 636).

In the response of leaves to light obtained by the
method of resistivity variation, the preliminary effect of
chloroform is an enhancement which is followed by a
depression (p. 812 1.

'•<<)0 t.Ml'] >[()VHMFATS ]\ TT.ANTS

Jii:\ril-Si'ASM l\ PLANTS AND TRANSMISSION oF
DKA'I |[-KX('lTATION.

\\ lieii it |)laiit ()r;^aii is gradually laiscd in toiiiperatiire,
;i (leatli-spasni occurs, at a certain critical temperature, at
or near ()(l°('. A puKinated leaf, or an anisotropic (^)rj^an
I'xluhits a spasmodic dow n-mo\ement : a radial or;^an shows
sudden contraction. The plant is killed after the attain-
ment of the fatal temperature. 'I'he intense deatli-excita-
tion is also exhibited hy an al)riij)t electric response of
^alvanometric iiej^ativity, and l)y a sudden diminution of
electric resistance (p. 6*.)-i>.

The occurrence of the death-excitation is also d(Mnons-
Irated hy the transmitted effect ; when the lower end of the
plant is suhjected to the deat li-t(Mnj)erature, an excitatory
impulse is generated at or aiiout (iO^C. which canses the
successive fall of the motile leaf or leaflets higher nji the
plant.

The onset of local death caused h\ application of poison
gives ris(> to a similar excitatory impulse, which is trans-
mitt(Ml to a distance (p. 7s| ,.

NKRVors IMITI-SI'; IN I'l.ANTS.

Ordinary tis'^ues ai"e senu-conduct in;^ and tli(> contrac-
tile effect of stimulus remains localised. There are. how-
ever, certain tissues characterised hy a more or less
pi'otoplasmic continuity: excitation initiated at an\ point of
such a tissue is transnntted to a distance w it li a detinite \elo-
( ity. I)y means of the l''dectiic I'rohe this conducting; tissue
has heeii localised in the [ihloeni of the fil)i'o-\ ascular hundle.
The xylem is a non-conductor: and this is more or less
true of the mass of the cortex and of the pith ip-. 708).
The conduction of excitation is ari'ested hy the application
of \arioiis plivsiolo;^ica I hlocks : thus an eleeti'olonie l^lock

C.ENERAl, rtr.VTE'W 861

arrests the coiulnction diirinji the apphcatioii of the current,
the conduction beinf> restored on its cessation of the current.
Rise of temperature enhances, and fall of temperature lowers
the rate of conduction. Excitation is transmitted in. both
directions: the centrifuj^al velocity is greater than the cen-
tripetal. Local application of cold depresses or arrests
conduction, while application of poison permanently
abolishes the conthiction.

The power of conduction is modified by season. l)eing
higher in summer than in winter; it is also modified by age.
The conducting" power is low in young specimens, and
maximum in fully grown organs ; a decline of conductivity
sets in with age. The tonic condition of the tissue has an
influence on the conductivity. In an optimum condition
the velocity of transmission of excitation is the same for
feeble or strong stimulus. Excessive stimulation induces a
temporary depression of the conducting power. The effects
are different in a sub-tonic specimen ; in such a case, velocity
of transmission increases with the intensity of stinudus, and
the after-effect is an enhancement of the conducting power.
In non-conducting young organs a conducting path is
canalised by the action of stimulus (pp. 106, 757).

There is a particular aspect of the action of stinnilus
which is of fundamental importance in the life of the plant.
The continuance of its normal functions depends on external
.stimulus to maintain the tissue in an optimum tonic con-
dition; for denrivation of stimulus I'educes the plant to
an atonic condition, in which all life-activities are brought
to a standstill. The internal activity of the plant is also
dependent on external stimulation. Turning our attention
to particular instances, we find that growth and movement
in plants depend on the turg-d condition of the tissue, which
is determined by the cellula.' activity which maintains the
ascent of sap. When the -plant is cut off from the stimulus

862 LU'-E MOvraiF.NTS in plants

of its eiivironnieiit, tlie ascent of sa]) undergoes a decline
which ciihninates in an arrest.

It is thus clear that for the maintenance of the ascent
of sap in a tree the internal cortex should he excited through-
out its length either hy direct or hy transmitted stimulation.
As for the great lengtii of the cortex in the trunk of the tree,
covered as it is by the thick bark, direct stimulation of the
active iTiternal cells by external stimulus is impossible; it
can only be etfetted by transmitted stimulation. There
thus arise two questions : the first relates to the external
stinudus which by its transmitted excitation maintains the
cellular activity of the internal cortex ; the second relates
to the nervous ])ath l)y which the excitation reaches that
active layer.

Among the external stimuli, none is so wdely available
as that of light. Its stimulating effect can be transmitted
to a distance by the nervous channel, which is the phloem
in the vascular tissue. The vascular bundles again are
spread out in fine remifications as veins in the leaves. The
expanded lamina is thus not merely a specialised structure
for photosynthesis, but also a catchment-basin for the
stinudus of light, the excitatory effect of which is gathered
into larger and larger nerve trunks for transmission to the
interior of the plant. It is very significant that the internal
cortex in which pulsatory activity is to be maintained abuts
against the phloem through which excitation from outside
is being conducted.*

It is thus seen how all parts of the plant are, by means
of nerve-conduction, become not merely energised but also
put in the most intimate comnumication with each other.
It is then in virtue of the existence of such nerves, that the
plant constitutes a single organised whole, each of whose
parts is affected by every influence that falls upon any other.

* cf. Physiology of the Ascent of Sap.

GENERAL REVIEW 8G'i\

THE HYDKArLTC AXD THE XERVoTS REFLEX.

In a plant subjected to drouglit, irrigation at the root
causes a movement of water upwards with a definite velo-
city: this hydraulic impulse causes an increase of turgor
from below u[)wards, and the drooping leaves become
erected. An example of this was given where irrigation of
I\[i))iosa gave rise to the erectile response of the distant leaf
p. 80). If instead of irrigation we apply a strong" stinndus to
the root, say a prick with a pin or an electric shock from an
induction coil, the transmitted nervous impulse induces a
fall of the leaf, llic liydrauJic impulse is tlius antagonisti •
to the nervous impulse. Even in ordinary response and
recovery we observe these opposite actions. The erectile
movement of the leaf is due to the ascent of sap to the
pulvinus along" a definite channel. Stimulation of the leaf
induces a contraction and expulsion of water from the
pulvinus which escapes by the same channel through which
the ascent took place, but this time in a reverse direction.
The two phases of the normal response, viz., the excitatory
down movement followed by erectile recovery are thus
brought about by the excitatory and hydraulic actions
respectively. The fact that the hydraulic expansion opposes
and may even neutralise the excitatory action is seen in the
response of MiDiosa. The apparent insensitiveness of the
plant early in the morning is partly due to the excessive
turgor of the pulvinus at that time of the day. Again,
application of water to the pulvinus induces an expansion
and inhibition of response which may be restored by the
withdrawal of the excess of water by glycerin.*

The term " reflex ' has been defined as the reaction in
which there follows on an ir.itiating reaction, an end-effect
reached through the mediation of a conductor itself in-
capable of the end-effect.
* Irritability of Plants, p. 88.

^••4 LTFE :^10VKMKNT.S IN PLANTS

NTow tli(> iii\isihlt' liydniiilic iinpiilsc initiated 1)\- ilu'
irri<4ati()n of tho root causes an ciKl-cd'cct , nainely the erectile
response of tlie leaf at a distance; we mav therefore rejjiard
tlie particular elVect produced at a distance^ as tlie hiidraiilic
rcfti.r. Tliei-e is a diU'erent end-eU'ect. due to transmission
of excitation tlu'taiuli the i^Iant-nerve ^^■llich causes the fall
of \o\\\ : this is the ttcrvoiin rcftc.r \ the h\draulic reflex
in(luc(>s. as alreadv stated, an (^xpansive and tli" nerv;-,-
retlex a contractile end-etfec t A conijilexitv thus arises in
the motile response of ^ro\\ni^' and of pulvinated or<,'ans due
to the two reflexes anta^on!sin<i each otlier. The recopini-
tion of tlu> existence of these two distinct reflexes makes it
possihle to offer a full explanation of \arious effects wliicln
have liith(M'to appeared to he anomalous.

THonc MOM'.MKXT l"Xl)I':ii rNTT;.\TI';FiAT, STniULUS.

All tropic ciM'vatiU'es undei" diverse modes of stimidation
in puhinated and ^^rowiuf^' organs are dui^ to : (a')
the action of stinnilus cansin<>" a diminution of turgor and
contraction at the directly stinnilated proximal side of the
orjian, and (/»i increast^ of tni'^or and ex[)ansion at the in-
directly stinnilated distal side. In p'owin^" organs an
induced diminution of turgor is attended by a retardation,
and an increase of tiM-<ior by an enhancement of j^rowth.
T\)sitive curvatures t(>wards the stinndus ai'e thus caused by
the joiut effects of the contraction of the proximal and
expansion of the distal side. 'i'he fact that the stimulus
applied at one side causes an increase of tui-^ior at the dia-
metrically o[)posite side has l>een demonstiated. by stiimda-
tion of one side of the stem, which caused the erectile
movement of the motile leaf at the opposite side (p. 281).

Tlie following laws of etl'ects of Direct and Indirect
stimulus detertnine the varied moxcments of plants.

(iHNKRAL KKVIKW H6!'>

1. All loi-iiis of Direct stimuli iiuliict' contraction or
retardation of ;L;i"o\vtli, iiul Indirect stiiindi expansion or
acceleration of growth.

2. Unilateral stinuihis induces a positive curvature by
the contraction of the jM"oxinial, and ex])ansion of the distal
side.

;}. Transverse conduction of excitation neutralises, or
reverses the positive curvature. This effect is accentuated
hy the differential excitabilities of the upper and the under
halves of the anisotropic organ. Excitation internally
diffused induces effect similar to diffuse external stimulus.

4. The effect of rise of temperature is opposite to that
of the stimulus of light.

MECHANOTROPIS^r : TWINING OF TP^NDRILLS.

It has been repeatedly :hown that direct stimulations of
all kinds induce contraction, and retardation of growth, while
indirect stimulations cause an acceleration of the rate of
growth (p. -21)1). Under unilateral mechanical stimulus of
short duration, the directly stimulated proximal side of a
tendril undergoes contraction, and the indirectly stimulated
distal side show^s the opposite effect of expansion ; a positive
curvature is thus produced, w-ith a movement towards the
stimulus. The after-effect of direct stimulus is an accelera-
tion of growth al)ove the normal, hence after brief unilateral
stimulation, the stimulated side undergoes an acceleration
of growth and expansion, by which the recovery is hastened
(p. 300). This positive after-effect of stimulus on growth is
seen in the balanced record o^ growth (p. 82o). Btimulation of
one side of the tendril induces an expansion of the opposite
side (effect of indirect stimulus), even in cases where the
contractility of the stimulated side is feeble. Hence
response to direct stimulation of the more excitable side of

<?t)t) LTFE MOVEMENTS IN PLANTS

the tciidiil iii;iy 1)1' iiiliihitcd by the stunulatioii of the
opposite side (p. 'MO).

PHOTOTKOPISM.

Quantitative relation. — The positive heliotropic curva-
ture of pulvinated and growing organs is explained by
considerations given above, namely, the contraction of the
proximal and expansion of tlie indirectly stimulated distal
side. It is shown that the amount of heliotrojjic curvature
depends, (1) on the intensity of light, (2) on the sine of the
<lirective angle, and (3) on the duration of exposure. The
intensity of phototroi)ic action is thus dependent on the
quantity of incident light (p. 345).

Negative iLeliotropis))!. — When the light is very strong
and long continued, the excitation is transmitted across the
organ and induces contraction of the further side, which
neutralises the positive curvature. The organ now places
itself at right angles to the light, this being the dia-helio-
tropic position. In certain cases, the transverse conductivity
is considerable, the result of w-hich is an enhanced excitation
of the further side, while the contraction of the near side
is reduced on account of fatigue caused by over-excitation.
The organ thus bends away from light, exhibiting the so-
called negative heliotropism (p. 337).

Effects of different rays of the spectrum. — The
retardation of growth is one of the factors in the induction
of the phototrcpic curvature. The ultra-violet rays induce
the most intense reaction in retardation of growth ; the
blue rays are also effective, but the yellow^ and the red rays
are relatively ineffective (p. 211). In the infra-red region
the thermal rays also are very effective in inducing tropic
curvature; we thus obtain positive, dia-, and negative radio-
thermotropic phenomena, parallel to those under visible

GENERAL REVIEW ^'67

radiation ([>. 415). The effects of rise of temperature and of
direct radiation are, however, antagonistic to each other
(p. 415).

Beyond the infra-red we enter the vast range of electric
radiation and to this also the ])lant is shown to be sensitive.
Like light, feeble electric radiation gives rise to an accelera-
tion, and strong radiation to a retardation of grow^th.
Parallel effects are obtained in the electric response of plants
to wireless stimulation (p. 424).

TJic co})ipJete pJwtotropic curve. — This consists of four
parts : (1) the stage of sub-minimal stimulation, (2) the stage
of increasing positive curvature reaching a maximum, (3)
the stage of neutralisation, and (4) the stage of reversal into
negative. Confining our attention to the second stage, the
susceptibility for excitation is found to be feeble at the
beginning ; it increases very rapidly with increasing inten-
sity or duration of stumulus ; the reaction then reaches a
limit. As regards the complete phototropic curve, the first
part is negative due to the physiological expansion induced
by sub-minimal stimulus. The curve then crosses the
abscissa upwards, and the positive curvature re-aches a
maximum. Owing to transverse conduction of excitation^
there is a subsequent neutralisation and reversal into
negative. Weber's law is not applicable for the entire range
of stimulation. His quantitative relation fails in the region
of sul)-minimal stimulus, where the physiological reaction
becomes qualitatively different, (p. 361).

Pliototropic torsion. — Lateral stimuli of all kinds
induce a torsional response in a dorsi-ventral organ, the
direction of torsion being such that the less excitable half
of the organ is made to face the stimulus. The torsional
movements of leaves ?.nd leaflets of many plants are
explained by the above definite reaction. The excitatory
efficiencies of two different stimuli may be compared by the

.SOS LIFE ]\rOVEMENTS IN PLANTS

Torsional Balance l)y allowing tliem to act on the two flanks
of the organ (p. 409).

Ill A-ni'll.loTnol'TC Ali.irSTMl'.NT OF TJvWFS rXDRii
li; WSM! •'■|i;i) I'.XCITATION.

T)ia-heliotro|)isin is clia''acteristically exlii])ite(l hy dorsi-
Aentral organs such as leaves. Heliotropic adjustment
is shown to take placi' under ti'ansinitted excitation
in Mi)ii<)S<i and in II ilniiithus, chosen as represen-
tatives of sensitive and ordinary plants. Tlie foui-
quadrants of the j)ulviiuis of Mi})K)S(i function as
four distinct effectors. There are separate nerve strands
which connect tlie four suh-})etioles with the four qnadrants
^)f the pulvinus. Hence the stinudation of the right suh-
petiole hy liglit gives rise to a transmitted nervous impulse,
which reaches the right (ju;ulrant and causes a right-lianded
torsion. Stinudation of the left sub-petiole causes, on the
otlier han«i, a left-handed torsion. Finally, stimulus applied
to the second and the third sul)-})etioles causes respectively
the down- and uj)-nio\ement.-;

.\ single reflex caused hy the stimidation of one of thf
«ub-petioles gives rise to a j)urposeless movement in one
direction which (tarries the plane of the leaflet away from
the position perpendicular to the incident light. But when
the two sub-petioles : (1) ami (4) are simnltaneously exposed
to light of the same intensity, the two resulting torsions
balance each other. Henco the lateral adjustments of the
leaf as a whole are made by the two sub-petioles (1) and
<4) which are situated outside ; the balancing adjustments,
u|) or down, ;ire made in r(>s|)onse to the excitations trans-
mitted, by the two middle sub-petioles ('2) and (3). It is
thus seen that equilibrium h only possible when the entire
leaf-surface (consisting of the rows of leaflets carried by the
four sub-petiole^i) is equallv illuminated ; and this can only

GENERAL REVIEW 8('if>

occur wlien the leal' surface as a wliole is perpenilieular to
the incident hj^ht. The leal" is adjusted in space by the
co-ordinated action of the four reflexes. The dia-heiiotropic
attitude of the leaves is thus brought about by distinct
nervous impulses, initiated a* the perceptive region actuating
th<^ different effectors at a distance (p. 746).

1' BOTOX A sr J C C U R V ATURE S .

There is no line of dcinarcation between tropic
and nastic movements. In an organ exhibiting
difference of excitability at the opposite sides, strong
unilateral stimulus becomes internally diffused, and
causes greater contraction of the more excitable side of the
organ. Two different effects are produced which are deter-
mined by the transverse conductivity of the organ. In the
absence of transverse conduction, the positive curvature
reaches a maximum without neutralisation or reversal. The
leaflets of Enithri}m indica and of CUtoria ternata thus fold
upwards, the apices of their leaflets pointing towards the
sun. But in organs in which the power of transverse con-
duction is considerable, the excitation under strong light
becomes internally diffused, and gives rise to the greater
contraction of the more excitable half of the organ. This
explains the so-called " midday sleep " by the upward
folding of the Mimosa leaflet and downward folding of the
leaflet of Biophytinu and of Averrlwa, under the action of
the rays of the sun (p. 548\

NIGHT AND DAY MOVEMENTS IN PLANTS.

The diurnal movements of plants are complicated by
several phenomena, the most important of which are, (1) ther-
mionastic movement caused by the differential growth of the
two sides of the organ under diurnal variation of tempera-
ture, (2) thermo-geotropism, due to variation of temperature

^"t^^ LIFE MOVEMENTS IN PLANTS

affecting geotiopic action, and {'-i) the recurrent responses
to light and darkness.

TlicrDKnidstij. — Tiicrnioiiastic movements are well
illustrated in the water-lily \ ijmphdcti. In India the
perianth leaves begin to o[)en in the evening with the falling
temperature; the flower is lound to become full,y expanded
by 10 P.>r. The movement of closure sets in wdth rising
temperature in the morning, the liower becoming closed by
10 A.M. (p. o'rl).

T]icr))io-(jCotropis)ii. — Of the number of diurnal move-
ments in plants the largest are due to a cause hitherto
unsuspected, viz., the effect of moderate variation of tem-
perature on geotropic action which is accentuated during fall
of temperature and depressed diu'ing rise of temperature.
This particular effect was first discovered in the Praying
Pahit of Faridpur which grew at an inclination of about
00° to the vertical, and was thus effectively std)jected to the
stimulus of gravity. This tree daily exliibited a continuous
fall, till the maxinnnn was reached between "2 to 3 p.m.
when the day's temperature was at its highest; the move-
ment was then reversed with the fall of temperatiu'e, till
the tree attained its highest erection at about <> A.:\r. next
nioi-ning, when the temperatiu'e was at its lowest (p. 7t.
The particular diurnal iiioxcnuMit was next found in (jther
j)alm trees, and also in all j)lant-organs which respond to
the stiimdus of gravity (p. VjS). This thermo-geotropic
response is experimentally shown t(j occur in rigid trees, in
stems, and in leaves of [)lants. The diiu-nal record in all
these exhibits an erectile movement from thermal noon to
thermal dawn, and a jnovement of fall from thermal dawn
to thermal noon.

In contrast with the ordinaiy thermonastic movement
which is confined to growing organs, the thermo-geotropic
movement is found to take place not only in iht^ growing

CrNi-:!; \I. I'FVIKW Hll

l)nt iilsi) ill riilly ^i(-\\ii (irgaiis, iiu'liiding rigid trees.
Again, tlieiiiiDiia.st ic iiioviMuciit is not affected by gravity,
but thenno-geotro[)ic response is determined by the
directive action of gravity and, therefore, becomes reversed
in an inverti^d plant. The factor of stiniuhis of gravity in
therino-geotropic phenomena thus hecomes estabhshed.
As regards the influence of temperatuii', it is demonstrated
in two chfferent ways. First, by iiuhicing a change of the
daily rhythm by experinicnrally reversing the iiatnial
perioils of maximum and minimum temperature, and
secondly, by the aboHtion of periodic movement altogether,
by keeping" the plant at a constant temperature (pp. 519,
.•")68).

I'lic Sclt-Hcc' rdnri lliuhaurapli . — .\mong the important
factors in causing movements in j)lants are the variation of
temperature and of the intensity of light. The variation of
temperature is automatically rec( rded by the compound
.'trip of two metals whose expansions are unequal. There
IS, however, no apparatus for detection and record of varia-
tion in the intensity of ligJit from hour to horn* This
difficulty has been overcome by the invention of the Self-
recording Radiograph, in which a selenium cell is put in the
fourth arm of a Wheatstone Bridge and balance secured in
darkness. On exposure of the selenium cell to the light of
the sky, the balance is up-^^et, the galvanometric deflection
being proportional to the intensity of light. By automatic
mechanism the selenium cell is exposed to light for a
definite length of time, '^nd the galvanometer deflection
recorded on a moving piece of paper. This is done
every quarter of an hour, or every hour according to the
requirements. Tt is thus found that the intencity of day
light increases rapidly till the maximiun is attained at noon.
The maximum rise of Temperature is, however, attained
much later, the thermal noon being about 2-30 p.i^j. The

S

^7:^ LIFE MOVEMENTS IN PLANTS

intensity of light gradually declines till about 5 p.ai., after
which the diminution of light is very abrupt.

Diurnal movement due to alternation of light and
darkness. — In the leaflets of Cassia alata the effect of light
is predominant, compared with that of temperature. The
leaflets begin to close when the light is undergoing a rapid
diminution after 5 p.m., the closure being completed by 9
P.M. The leaflets remain closed till 5 a.m. next morning,
after which the}^ begin to open wth the light, and become
fully expanded by 9 a.m. (p. 544). The large terminal
leaflet of Desmodium exhibits diurnal movement similar to
that of Cassia (p. 542).

Diurnal niovement of the leaf of Mimosa. — The leaf is
responsive both to the acticn of gravity and of light.
The operative factors in tlie diurnal movement are : (a) the
variation of geotropic action Vv'ith changing temperature, and
(6) the response to the action of light which, generally
speaking, is antagonistic to that of rise of temperature.
Under thermo-geotropic action the maximum fall of the leaf
takes place at thermal noon, which is about '2 p.m. the
maximum rise being at thermal dawn, about 6 a.m.

Tn the forenoon, rise of temperature causes a fall of
leaf, but continuous light acting from above tends to raise
it. The rnpid (liiiiiiiiition of light towards evening acts
virtually as a stimulus, causing an abrupt fall of the leaf.
The diurnal movement of Mimosa thus exhibits four phases,
(1) The leaf owing to fall of temperature erects itself from
2 to 5-30 P.M. or thereabouts, (2) About G v.isi. there is a
rapid diminution of light and the leaf undergoes a sudden
fall, which continues till about 9 p.m. (3) After 9 p.m.
the leaf begins to erect itself during the fall of temperature,
the maximum erection being attained at thermal dawn
which is at or about 6 a.m. (4) Tn the forenoon the leaf is
acted on by two antagonisMr react irns, the effect of rising

GENERAL RT'VIEW S/"^

tein[)ei;Hin\' ;iiul of iiU'iVii.'^iiip liylit, tlic ellect of tem-
perature l»eing pre(lomi)i;iiit. The leaf thus continues to
fall till tli<M-ni;il iiooii. wliich is ahout "2 P.M. The diurnal
curves of the petioles of Cassia alata and of Ifrliinitliiis
animus are similar to that of Mimosa (p. 597).

GEOTROPISM.

Mechanical response. — The stimuhis of gravity is
shown to induce an excitatory reaction similar to that under
other forms of stimulation. The upper side of the horizon-
tally laid shoot is directly stimulated and undergoes contrac-
tion (p. 440).

Electric response. — The excitatory reaction of the
upper side is exhibited by an induced change of galvano-
metric negativity. The lower side shows a change of
galvanometric positivity indicative of increase of turgor
and enhancement of the rate of growth (p. 447). The
method of geo-electric response is more sensitive in the
detection and quantitative determination of the effect of
stimulus of gravity than the method of mechanical response.

Explanations of opposite reactions at different sides of
the organ. — The geotropic up-curvature is only possible by
differential reaction at opposite sides of the organ ; this is
demonstrated by the results of electric investigations which
show^ that the upper side exhibits contraction, w^hile the
lower undergoes expansion. It is further shown that this
difference in the reaction is due to the fact that the stimulus
is direct at the upper and i'nlirect at the lower side (p. 610).

Geotropic excitations at various angles. — The excita-
tion is found to increase as the sine of the angle of inclina-
tion. This relation is only approximate, for the excitation
is relatively greater at larger angles than the value deduced
from the law- of sines (p. 625).

The critical angle for immediate geotropic excitation. —
The excitation at lower angles is disproportionately less: tha

.S7-I LJ1''K iMOVI'hMi'lNTS IN IT.ANTS

(livtT^ciici" Ix'twcen tlic sines mid cxcitnt ions is xcry slight
jihove lo°. while it is \ei'y [uonoiiiieed ;it the IowcM' angle
ol' ;5-")°. The cMirve of e\eit;ili()n ;it dinunishin;^ ;in;^les
when produced hackwai'ds cuts the abscissa at about Ml. 5°
at which an<iie, the geo-electric excitation would he reduced
to /.iM'o. The results of cxpciiuients show the existence ol
such a critical angle at about ."^2°. 'i'lie theory of statoliths
obtains strong" support From this particidar plienonienon, for
an increase above the critical angle is found to give rise to
an ahni^it excitatory geo-electric i'(>spous(> (p. HiU)) This
must evidently be due to the sudden fall of tlic lieavy parti-
cles from the base to the side of the geo-perceptive cells.

(icotropir torsion .— l\\ dorsi-ventral organs lateral
application of any form of stinmlus gives I'ise to a torsional
response by which the less excitable half of the organ is
made to face the stimulus. A geotropic torsion is produced
when [\\c j)lant is [)laced on one side, so that the vertical
lines of force of gravity strike at one of the two flanks of
the organ, (leotropic stimulation of the right flank give.-
rise to a right-handed, that of the left (lank, to a left-handed
torsion (p. oO'l). Torsions induced by two different modes
of stimulatioii, say of graxity and of light, may thus be
compared by making them act simultaneously at the two
opposite llaidvs of the organ (p. oOo).

Effect of narcotics. — The general effects of narcotics
'lave already been explained in connection with their action
on all modes of stimulation. Carbon dioxide induces a preli-
minary enhancement of geotro[)ic response followed hy a
decline and even a reversal. Tlie effect of dilute vapour of
ether is to cause a great increase in geotropic curvature.
Ohloroform vapour causes an enhancement followed by an
a 1 rest of geotropic action.

Kfjcct of raridtioii of t(nij>( ratitrc. — The thermo-
geotrojiie action lia^ been shown to cause a dimimition in

GENRHAL UK VIEW Hi i't

^t'ittiojiic (iiivatnrc lUirinj^" rise, aiul ;ui increase during fall
oi' temperature. 'Ihe geotropic torsion is similarly
decreased during the rise and increased during the fall of
temperature. X'ariation of tem])erature also modifies tlie
position of dia-geotropic equilibrium (p. 519).

Ldcalisatio}} of (jco-perccpiirc layer. — Electric investi-
gations su|)i)ort the theory that it is the weight of the heavy
particle^ which causes geotropic stinudation in tlic higher
plants. The geo-perceptive layer has been localised by the
Electric Probe and found to coincide with the endodcrmal
starch-sheath. In certain plants the geo-electric distribu-
tion exhibits two maxima. Microscopic section showed
that the starch-sheath in these is not single but double, and
that the positions of the two electric maxima coincidv^ with
those of the two starch-she;itiis (p. 618).

Dia-(ic(itroi)is)n of (hn-si-rciitral organs. — This parti-
cular adjustment under geotropic stimulation is shown to be
due to the irritation caused by pressure of heavy particles on
<-ells which are unequally excitable at the ujiper and lower
sides of the organ (p. 726).

Geotropism of rootfs. — On subjection of the tip of the
root to the stimulus of gravity, its upper side exhibits
excitatory reaction of the galvanometric negativity. This
shows that the root-tip undergoes direct stimulation.

The electric response in the growing region above the
stimulated point of the root-tip is positive, indicative of
inci-ease of turgor and expansion. This is due to the effect
of indirect stimulus.

The stimulus of gravity is perceived at the root-tij) and
the responsive movement takes place at the distant growing
region. Geotropic stimtdaiion of the root is thus indirect

(p. 473).

In contrast with the above is the fact that the growing
region of the shoot is both sensitive and responsive to geo-
tropic stimulus.

876 LIFE MOVEMENTS IH I'l.ANiS

As the effects of direct and indirect stiiniilation on
growth are antithetic, the responses of shoot and root to the
direct and indirect stimulus must be of ()i)posite signs.
There is thus no necessity for postulating two different irri-
tabilities for the shoot jind the root, since tissues in general
exhibit positive and negative curvatiu-es according as the
stimulus is direct or indirect (p. 476) .

A plant is acted on by gravity, by hght and its diurnal
variation, by changing temperature, by drought and rain,
not to mention many other stimuli of its environment. For
obtaining some idea of the great com])lexity whicli arises
from the varied reactions we may watcli a Miiiiosa plant
watered at intervals and observe specially the effects of two
out of many stimuli of its environment, namely those of
light and of gravity. In the movement of Mimosa leaf
there are then the following variable factors: (1) the
hydraulic reflex due to the ascent of saj) which causes an
erectile movement antagonistic to the excitatory fall of the
leaf; ^2) the different effects of direct and indirect stinnda-
tion, examplified by the fall of the leaf under stimulu.«
directly applied to the pulvinus in contrast with the erectile
movement caused by a similar stiniuhis indirectly
applied, i.e., at the point of the stem opposite to the pul-
vinus (p. 281) ; (3) the reflex caused by tlic stinndus of light
acting on the four sub-petioles beariuii tlic Icailcts, in this
there are foui- modiiying snl)-factors wliicli dcpcMul on the
relative intensities of excitation transmitted from the four
distinct receptors of light-stimulus; (4t the geotropic
stimulus which acts on the four quadrants of the pulvinus,
tlie res|)ousive peculiarity of each of these quadrants is
different from that of the others; and (5) the effect of
thermal variation in modification of geotroj)ic action.

The above example illustrates the extremely numerous

GENERAL REVIEW S77

variations in the responst' which must arise from the rom-
hinatiou of etl'ects of a larj^e miniber of factors, some of
which are concordant and others antagonistic. The problem
of plant-movement which confronts ns though bewildering
at first sight, is, however, not insoluble. By the isolation
of individual factors and separate investigations on them, it
is possible to unravel the complexity and discover a
}.y?neralisation for the life-movement in plants.

LITERATURE

Bayliss. W. M. — " Principles ol (jieneial Physiology " — (1915).
Blackmax, V. H. AND Paine.- ' Annals of Botany "" — vol. xxxiii,

No. cxxxv— (191S).
BOSE J. C. — " Response in ihi; J.i\ ing and Xon-Living " — (1902).
,, •• Plant Response "—1906.

,, " Comparative Electro Physiology " — 1907.

,, ■■ An Automatic Method for Investigation of Velo-

citj' of Transmission of Excitation in Mimosa "
—Phil., Trans., B, vol. 204, 1913.
,, " Researches on Irritability of Plants "—1913.

,, " On Diurnal Variation of Moto-Excitability of

Plants " — Annals of Hotany, vol. xxvii.
No. CA-iii,— 1913.
,, " The Influence of Homodromous and Heterodroni-

ous Electric Cui'rent on Transmission of Excita-
tion in Plant and Animal " — Roy. Soc. Proc.
B, vol. 88—1915.
AND S. C. Das — " Physiological Investigation with
Petiole Pulvinus Preparation of Mimosa
2)udira.'" Roy. Soc. Proc. B, vol. 89, 1916.
., AND G. Das — " Researches on Growth and Movement
in Plants by Means of the High Magnification
Crescograph " — Roy. Soc. Proc. B, vol. 90, —
1919.
.4ND S. C. GuH.A— " The Dia-Heliotropic Attitude of
Leaves as determined by Transmitted Nervous
Excitation," — Roy. Soc. Proc. B, vol. 93, 1922.
Haberl.andt, G.— " Physiological Plant Anatomy," (English

translation)— (1914).
JOST, L. — " Lectures on Plant Physiology," (English ti-ansla-

tion)— (1907).
Lynn, M. J. — " The Reversal of (ieotropic Response in the

Stem," The New Puytologist— (1921).
Pfeffer, W. — " Plant Physiology," (English Translation) —

(1903).
Vines, S. H.— " Lectures on Physiology of Plant,"— (1886)

INDKX

VOJ.ITMES I— IV.

A- and D- effects, 143, 223, 323, 354, 822.
Acid, action of, on pulsations of /)> yi/nx/iuni Icuflpt, DO.
Additive effect of stimulus, 8(il.

After-effect of homodromous aiul heterodroinous current, 123, 131.
of light, 509, of maximum, 572, of p)-(> maximum, 570,
of post-maximum, 572.
,, of stimulus on conductivity, 103.
Age, effect of, on geo-electric response, 454, 617.
,. on power of conduction, 100.
,, ,, ,, on thermo-geotropism, 562.

Alkali, action of, on pulsations of Desinodi ii m leaflet, 90
Allium, death-spasm of peduncle of, 691.
Ammonia, effect of, on growth, 184.
Ampelopsis, phototropic response o*^ tendril of, 391.
Anabolism, 143.

Anaesthetic, chamber foi' application of, 043
,, Death-spasm under, 648.

Different stages of action of, 644.
Effect of, on balanced growth, 266.
,, ., ,, on geotropic response, 650.

,, ., ,, on growth, 185, 641.

,, on resistivity variation, 812.
Method of application of, 643.
,, Modifying influence of, on response, 683.

Angle, critical, for geo electric excitation, 456, 631.
,, of incident light and tropic curvature, 343.
,, of inclination and geo-electric excitation, 620.
Anisotropic organ, phototropic response of, 379.

,, ,, response of, 34.

Anisotropy, Dia-geotropism and, 712.

Electric method of investigation of. 678.
Induction of, by gravitational stimulus, 076

I INDEX H81

i Anisotropy, Reversal of, usl.
Anode, effect of, on growth, 303.

Apo-geotropic curvature, variation of uniler thermal change, 516
Arenya sacchariftro, 18.

,, ,, Diurnal movement of, 20.

,, ,, ,, ,, ,, in absence of tran

spiration, 22.
,, ,, ,, ,, ,, in continued dark-

ness, 18.
,, „ ,, ,, ,, in inverted position,

23.
,, Effect of drought on, 19.

,, ,, ,, ,, poison on, 19.

Averrhoa hilimhi, control of transmitted excitation in, 109.
^Averrhon rarrmihohi, periods of positive and negative impulses in,
f 136.

,, preferential direction of conduction in, 99.

., ,, Velocity of conduction of excitation in, 99.

Autonomous pul.sations, continuity between multiple and, 772.

modification of. 228, 243.
,, ,, ,, . under diffuse light, 233.

,, ,. ., under temperature, 237.

of M/)/i(js(i i)ulvinus, 583.
,, ,, Record of, in Desmodium leaflet, 234.

Revival of, in Deamnr/ium leaflet, 228.
Axial rotation, method of, 449.

Balanced Crescograph, 258.

,, ,, calibration of, 260.

,, ,, principle of the method of, 256

,, ,, sensitiveness of, 262.

Balance of phototropic and geotropic torsion, 505
Barium chloride, effect on ^f{mo'<i response, 89.
Basella alba, death-spasm of, 693.

,, cordifolia, diurnal curve of, 25.
,, ,, reversal of natural rh;v+,hm of, 27.

Bindweed, response of root of, 463.
Bf'ophyfi/m sejisitivirm, 99.

,, ,, multiple response of, 784.

,, ,, transmitted death-excitation in, 783.

Blue light, effect on growth, 210.

,, ,, ,, ,, Mimosa response, 246.

Bryophyllum caJycinum, geo-electric distribution in stem of, 498.

882 ixDKx

BryophyDitv) c<ilyciiiin„, gco clcrtiic reaction at different depths,

485.
,. ., localisation of yeo ix'iceptive layer in,

488.

Calofiopis i/itjdiitra, resistivitx response of, 802.
■Cassin nlatn, dinrnal moNCMnent of leaflet, 538.
,, .. ,, ,, ,, petiole, 591.

,, ,, Effect of strong litilil on leaflet of, 405.

Torsional nioxcnicnt of leaflet of, 104.
iii()iit<in(i, 268.
Cathode, effect of, on growth, 302.

■Cai'bon dioxide, effect of, in reversal of geotiopic icsponse, 684.
,, ,, ,, on geo electric response, 671, 673.

,, ,, ,, ,, geotiopic action, 659.

,, ,, ,, ,, growth, 185, 265, 660, 668.

,, ,, ,, ,, organs contiacted under stimulus,

670.
,, ,, mechanical and electric pulsations

of Di'siiiod I II III , 772, 773.
,, ,, ,, ,, resistivity variation, sl2.

Cento iireo, effect of chloroform on growth of, 646.

localisation of geo |)eicepti\ c la.\er in, 613.
Chloi-oform, (>ffecl of, on balanced gi'owth, 267.

,, ,, ,. geoti'0))ic curvature, 656.

,, ,, ,. gi'owing organs, 646.

,, ,, ,, resisti\it> variation, S12.

,, ,, ,, response of geotropically curved

organs, 684.
•Clitorln ternatea, ]iara-heliotropic lesponse of, 381.
Coagulation, inadecpiacy of, in explaining death-spasm, 690.
Coal gas. effect of. on response undei- balanced torsion, 507.

., growth, ISG.
(U))irn\(hiiiii hf lu/dlinsif!, critical angle for geo electric excitation

of, 638.
,, ,, localisation of geo-percejitive layer in, 613.

Compound lever. l.")7.
Conducting jialh in plants, 706.

fashioned V)v stinuilus, 757.
'Conduction of excitation, diiective action of current on. 113.

T^ffect of age on, 100.
,, ,, ., season on, 100.

■ ,, ,, ))refer(>ntial direction of, 90.

INDI \ 8b."i

,, prort'ss of, Ub.

Conductivity Kalaiu'c, iiu-thod of, loT.
Continuity between abnormal antl normal responses, 223.
actual and incipient contraction, 19S.
ordinary and multiple responses, 769.
multiple and autonomous responses, 772.
i'linrol riiluiis, localisation of geo-pciceiitive layer in, 614.
Cortex, electric excitation in, 7(i3.
Crescograph, Balanced, -Ibb.

,, Demonstration, 17U.

,, High Magnification. 157, iSVl.

Magnetic, 169.
C rill It HI, complete geotropic curve of, 435.
Effect of ether on growtli of, 645.

,, chloroform on giowth of, 647.
time-relations of responsive growth variations in, 166.
,, tropic curvature of, 276.
Critical angle for geo-electric excitation, 631.

., ,, ,, ,, and statolith theory, 640.

,, ,, ,, determination of, 635.

,, ,, ,, lowering of, by repeti-

tion, 639.
Critical temperature for transmission of death-excitation, 777.
Groton, diurnal record of leaf of, 558.
Cvcurhita Pepo, tendril of, 290.

,, ,, ,, effect of light on hyponastic move-

ment of, 529.
,, ,, effect of stimulus on growth of, 292.

Current, directive action on conduction, 113.
effect of, on latent period, 120.

,, ,, ,, velocity of transmission, 119.
influence of direction of, in animal, 125.
,, ,, ,, ,, in plant, 115.

,, ,, ,, on direct and indirect stimu-

lation, 130.
polar effect of, on excitability. 111.
up-hill and down-hill, 122.
Curvature, positive and negative, 272.

Dahlia, diurnal record of leaf of, 558.
Darkness, response of Mimosa in, 593.

sudden, effect on Mimosa response, 53.
Bniiira (ilha, effect of chloroform on growth of, 647.

884 INDEX

Datura altia, revivul of growth in mature style, 230.
D-eft'eet, 143, 223, 354, 822.
Death-excitation, transmission of, 776.
I>i.-ath-spasm, excitatory character of, 690.

in geotropically curved organs, 687.
,, ,, under chloroform, 647.

Death temperature, determination of, 688.
,, ,, electric spasm at, 692.

Desniodium gyrans, antagonistic effect of acid and alkali in pulsa
tions of, 90.
,, ,, complete phototropic curve of terminal leaf

358.
,, ,, day and night position of terminal leaf, 541

,, ,, death-spasm in pulsating leaflet, 689.

,, ,, effect of carbon dioxide on mechanical anc

electric pulsation of, 771.
,, ,, „ chloroform on geotropic response

of, 656.
,, ,, ,, diffuse light on pulsation of, 235.

,, ,, ,, ether on geotropic response of, 654

,, ,, ,, increasing intensity of light, 339.

,, ,, record of pulsations of, 234.

,, ,, ,, diurnal movement of terminal leal

of, 542.
,, ,, revival of pulsation of, 228.

,, ,, tropic response of pulvinus of, 342.

Dessication, effect of, on nervous conduction in plants, 101.
iJia-geuLrupic equlibrium, determining conditions of, 724.

,, ,, effect of variation of temperature

on, 517.
,, ,, electiic investigations on, 723.

Dia-geotropism, causes of, 713.

,, changed to negative on inverting the organ, 710,

,, characteristics of, 712.

,, of dorsi- ventral organs, 710.

Dia-heliotropic attitude of leaves, 731.

,, explanation of, 746.

Dia hcliotropism, 733.
Diaphot'tropism, 328.
Dia-radic -thermotropism, 413.
Differefiuial excitability, determination of, 405.

,, ,, J'^ffect of, on geo-electric response, 455.

Geotropic, 439.

INDEX

885

Dissimilation, theory of, 11-2.
Diurmil movement, 523.

Alternation of light and, 531.
l^ffeot of variation of light on, 539.

,, temperature, 539.

in inverted position, 23, 566.
modification of, 561.
of curved stems, 557.
of 3Iiiiiosa and Ilelianthiis, 738.
predominant effect of light, 531.
reversal of, 27.
Thermo-geotropic, 554.
Thermonastic, 546.
Turning points of, 561.
variables in, 527.
Diurnal variation of light and temperature, 532.

,, ,, moto-excitability of Mimosa, 16, 43.

Dorsi-ventral organs, dia-geotropism of, 713.

,, ,, explanation of difference of geotropic

response of, 726.
,, ., geo-electric response of, 723.

,, ,, response to lateral stimulus, 704.

Dregea vohcbilis, response of, 413.
Dual, impulses, 136, 273.
Duplication of geo-perceptive layer, 614, 616.

Eclipta crecta, changes at upper and lower sides on geotropic
curvature, 718.
,, ,, effect of chloroform on geotropic curvature of, 656.

Effectors, in Mimosa pulvinus, 70S.
! Ir.liii- excitation in different layers of Mimosa petiole, 703.

,, localisation of geo-perceptive layer, 484, 599.
Electric Probe, 483, 601.

,, ,, exploration of geo-perceptive layer by, 484, 479, 599.

,, ,, localisation of nervous tissue in Mimosa by, 701.

Electric resistance, diminution of, by mechanical stimulus, 801.
increase of by sub-minimal stimulus, 810.
response bv variation of, 796, 805.
Electric response, effect of sub-minimal stimulus on, 809.

by Method of electromotive variation, 762.
,, ., ,, resistivitj^ variation, 796, 805.

of leaf under light, 838.
of Miirinxn pulvinus, 751.

SSC) INDi.X

Klcc'lric ri'spoiisc, Tlu' Quiulianl ^Mi'IIhmI ot, si 1.

to clii-('ct miilattM'al sliinulus, I I-"!.
,, ,, ,, iiidireft unilateral stimulus, 444, 4t)5.

,, ,, under electric stimulus, K05.

.- Iif;lil, ^11

nu'chuuical slimulus, 7!)().
j'llectric slux-k. cllect of duiation of, on growth, 197.
,, ., ,, intensity of on growth, KKi.

,, ,, tinu" relations of giowtli variation under. 168.

Electrodes, uou i)oIaiisable, 445.

Electrometer for determining velocity of Liunsniission, 762.
Erythriti'i iiiflica, 141.

Characteristic phototi'opic cui've of, 351.
,, ,, effect of cai'hou dio.xidc on geotropie response

of, 664.
,, ,, latent period of phototropic response of, 324.

,, ,, positive para-heliotropism of, 381.

pulvinus of, 326.
Ether, effect of, on geotrojiic curvature- of growing organs, 654.
,, ,, ,, ,. pulvinated ,, 653.

,, ,, growing organs, (ill.

,, ,, response of geot ro|)icall\ cui'ved oi'gans, 683

Excitability, change of, after inmiersion in water, 79.
,, Diurnal variation of, 61.

,, Effect of excessive turgoi' on, 55.

,, ,, high temperature on, 58

,, ,, low ,, ,, 56.

., ,, physiological iiH>rtia on, 68.

,, ,, season on, 69.

,, „ sudden darkness aiul its continuation on,

.53, 94.
,, Variation of, after section, 80.

in different hours of the day, 66
Excitation, conduction and convection of, 98.

,, transmission of, effect of age on, KKi.

,, ,, ,, ,, dessication on, 102.

,, ,, ,, ,, season on, 100.

,, ,, ,, ,, tonic condition on, 103.

,, ,, ,, electric control of, 109.

,, ,, ,, physiological block on, 9"

,, ,, ,, preferential direction of, 99.

,, ,, ,, temperature variation on, 100.

Excitatory effects of stimidi on ])ulvinated ami growing organ.i
244.

INDEX
Fatigue, Effect of, on response, 91.

887

Galvanograph, 829.

Galvanotropism, 301.

Geo-electric distribution, 497. 603, 616.

excitation, at angles above 45°, 624.
below 45°, 634.
45° and 135°, 627.
different layers, 606.
under side, 610.
characteristic sign of, at under side of

organ, 609, 610.
critical angle for, 631, 636.
curves for at various angles, 634.
curve of, 496, 603.
decline of, on two sides, 609.
effect of age on, 617.

relation between angle of inclination
and, 619.
Geo-electric response, angle of inclination and, 459.

,, ,, ,, vertical rotation and, 459.

,, ,, at different angles, 621.

,, ,, depths, 614.

,, ,, characteristics of, 451.

,, ,, effect of age on, 617.

,, ,, carbon dioxide on, 671.

,, ,, ,, differential excitability on, 455.

,, ,, .. high temperature, 490.

,, ,, ,, season and normal variation of

temperature, 604.
,, ,, entire cycle of, 458.

,, ,, experimental arrangement for, 445

,. ,. isolation of, on one side, 672

,, ,, of different layers, under side, 493, 610.

,, ,, ,, dorsi-ventral organs, 723.

,, ,, ,, growing region, 472.

,, ,, ,, lower side, 447, 629.

,, ,, ,, radial organs, 723.

,, ,, ,, root-tip, 468.

„ ,, ,, shoot, 442, 612.

,, ,, ,, upper side, 447, 611.

,, ,, physiological character of, 454.

,, ,, to direct stimulation, 443.

T

888 INDEX

Geo-eltH'tiic rospoiise to indirect stimulation, 441.

,, ,, variation of, at opposite sides, of geo-

,, ,, perceptive layers, 610.

vHi-iation of, temperature oJi, 605.
Geo-perceptioii at the root-tip, 474.

Geo-perceptive layer, electric excitation on two sides of, 609, 612.
„ ,, duplication of, 614, 615, 616.

„ ,, localisation of, 488, 599, 606, 613.

,, ,, maximum excitability of, 608.

,, ,, position of starch-sheath and, 489.

,, ,, transverse exploration of, 496.

Geotropically curved oigans, abnormal response of, 683.
,, ,, death-s])asm in, 693.

,, ,, ,, effect of ether on response of, 683.

Geotropic curvature, effect of carbon dioxide on, 659.
,, ,, M '> chloroform on, 656.

,, ,, ,, ,, ether on, 683.

,, ,, explanation of reversal of, 666.

Geotropic curve. Complete, 434.

,, ,, of spring and winter specimens, 652.

Geotropic excitability, 439.

Geotropic movement, and electric response, 462.
(>ffcct of cold on, 430.
,, ,, latent period of, 432.

,, ,, summation with })hototropic, 504.

,, ,, reversal of, under carbon dioxide, 664.

Geotropic leaction, and directive angle, 438.
,, ,, at lower side, 492, 494, 629.

,, ,, at upper side, 499, 629, 719.

,, ,, character of, 428.

,, ,, explanation of opposite signs of, 719.

tests of, 491.
Geotropic Recorder, 427.

Geotropic response, variation of temperature on, 604.
Geotropic stimulation, characteristic effects on 4 quadrants of

jmlvinus of Miinoxn, 714.
,, ,. mechanics of, in shoot and root, 475.

Geotropic stimulus, effective direction of, 435.

,, ,, Summation of, and of light, 436.

Geotropism, 425.

positive and negative, 43S.
(Jrowth. abnormal accelei-ation of, in subtonic sjiecimens, 219.
,, absolute rate of, 160, 261.

INDF.X 889

Growth, ae'tion of light on, 205.
,, cardinal points of, 177.
,, effect of ammonia, 186.
,, ,, anaesthetics, -26(5, 641.

carbon dioxide, 185, 265, 668.
,, ,, coal gas, 186.

., ,, continuous electric cuirent, 302.

light, 209.
,, ,. ,, stimulation, 197.

different rays, 209.
,, ,, ether, 185, 644.

,, ,, hydrogen peroxide, 184.

,, ,, increased hydrostatic pressure, 190.

,, ,, Indirect stimulus, 21.3.

,, ,, intensity of stimulus, 196, 207.

,, ,, irrigation, 190.

,, ,, mechanical stimulus, 203.

,, .. single spark, 325.

sulphuretted hydrogen, 186.
tempei'ature, 173.
., ,, variation of tension, 189.

„ ,, .. turgor, 193.

,, ,, wound, 203.

,, ,, wireless stimulation, 421.

,, Positive response of, under sub-minimal stimulus, 224.
Growth-pulse, 167.

Growth-rates for different temperatures, 181.
Growth Recorder, 157, 642.

Gi'owth movement, arrangements for compensations of, 257.
Growing organs, contractile response of, 241.

,, ,, effect of intensity of light on tropic curvatures

of, 341.
,, ,, ., chloroform, 646, on geotropic curvatures

of, 656.
„ ,, ,, ether on geotropic curvature of, 654.

,, ,, latent period and time relations of response of,

165, 201.

Helianfhus annuus, death spasm of, 688.

,, ,, Diurnal movement of, 738.

,, ,, effect of ether, 645.

,, ,, resistivity variation of, 807.

„ ,, torsional response of petiole, 740'.

S90 INDEX

HelianthiDi oiunius, transmitted excitation in, 743.
Heliotropic adjustment of leaves Explanation of, 742.

,, curvature, mechanism of, 737.

Heterodromous current, effect of in animal, 1-28.

,, ,, „ plant, 124.

Ilihiscus, rate of growth of pistil, 159.
High Magnification Crescograph, 157.

method of, 152.
Homodroraous current, after-effect of in animal, 128, 131.

plant, 124.
Hydrogen peroxide, effect of, on growth, 184.

,, ,, ,, on Mimo!in pulvinus, 88.

Hydraulic reflex, in plants, 863.
Hyponasty, 529.

,, effect of unilateral light on, 529.

Impatiens, resistivity variation of, 807.

,, transverse section of, 718.

Impulses, positive and negative, periods of transmission, 139.
Incipient contraction, 198.
Indirect stimulus, 135, 214.

,, ,, accelerating effect on growth, 216.

„ ,, effect of, on growth of tendril, 219.

,, ,, ,, on tropic curvature, 277.

„ „ effect on, Avtrrhoa, 136.

,, ,, unilateral application of, on tropic curvature,

277.
Infra-red light, effect on growth, 211.

,, ,, ,, Mimosa pulvinus, 247.

Inhibitory action of stimulus, 295.
Injury action of, on normal tissue, 104.

,, ,, on sub-tonic tissue, 105.

Jpomea reptans, 22.

,, pulchella, resistivity variation of, 807.
Irrigation, effect of, on growth, 190.

Lactic acid, effect of, on Mimosa response, 90.

Lactuca sativa, 841.

Latent period, effect of age on, 652.

,, ,, ,, current on, 120.

,, ,, of growth response, 165.

to light, 207.

,, ,, of phototropic reaction, 323.

INDEX 891

Lateral stimulation, effect of different modes of, 401.
Laws of Variation of Nervous Conduction under the action of

current, 133.
Effect of Direct and Indirect stimulus, 139, 217, -231.
Thermonastic reaction, 311.
Torsional response, 403.
Tropic cui'vature, 286.
Light, acceleration of growth under, 219.
,, action of, 315.

,, action on phototropic torsion, 400.
,, after-effect of, 569.

,, arrangement for local stimulation by, 367.
,, Critical intensity of, 320.

,, diffuse, effect on Des>noc/ii(vi pulsation, 235.
,, diurnal movement in absence of, 18.
,, Diurnal record of intensity of, 831.
,, effect of a single spark, on growth, 325.
,, ,, angle of inclination on phototropic curvature, 342.

,, ,, different rays on growth, 209, 210, 211.

,, ,, duration of exposure on phototropic curvatures,

344.
,, ,, on diurnal movement, 539.

,, ,, intensity of light, 207.

,, ,, on M 171108(1, 52, 94.

,, ircmediate and after-effect of, on growth, 319.
,, effect of, on pulvinated organ, 244.
,, ,, on torsional response, 405.

,, mechanical response of pulvinated and growing organs

under, 386.
„ normal effect of on growth, 206.
,, response to single spark of, 817.
,, stimulus of, and leaf adjustment, 739.
,, transmitted effect of, 362.
Localisation of, geo-perceptive layer, 478, 599, 606, 613.

,, ,, nervous tissue, 699.

Luff a aciitangula, 553.

Magnification, method of, 152.
Maximum temperature for growth, 178.

excitation for geotropic response, 608.
Mechanical response, of pulvinated and growing organs under

light, 242.
,, ,, of root to various stimuli, 461.

892 INDEX

Mechanical stimulus, effect of direct and indirect, on growth of

tendril, 293.
,, ,, effect of on ui-owth, 200.

Mechanotropism, 288.
Method of axial rotation. MU.
,, irrigation, 188.
,, vertical rotation, 458.

,, transverse exploration of geo-perceptlve layer, 496.
Midday sleep, 543.
Mimosa p«<^//rfl, autonomous j)ulsation of, 583.

,, ,, characteristic responses of different quadrants of

pulvinus of, 714.
,, ,, ,, ,, to transmitted excita-

tions from sub-
petioles, 697.
,, ,, complex res]K)nse of, to transmitted excitation,

695.
,, ,, death-spasm of, 688.

„ ,, definite innervation in petiole of, 706.

,, ,, dia-geotropic response of, 722.

,, ,, diuiiial movement of leaf of, 576.

,, ,, ,, variation of geotropic torsion, 581.

,, ,, ,, ,, moto-excitability in, 43, 61.

,, ,, effect of amputation of upper half of pulvinus

of, 84.
,, ,, effect of amputation of lower half of pulvinus

of, Sf).
,. ,, ,, carbon dioxide on geotropic curvature

of, 663.
,, ,, ,, Ijarium chloride on response of, 89.

,, ,, ,, ether on geotropic curvature of, 653.

,, ,, ,, excessive turgor on response of, 54.

,, ,, ,, fatigue on response of, 91.

,, ,, ,, hydrogen peroxide, 8S.

,, ,, ,, lactic acid and sodium hydroxide, 90.

,, ,, ,, light and ilarkness on response of, 52, 93.

,, ,, ,, physiological inertia on response of, 68.

,, ,, ,, season on response of, 69.

,, ,, .. weight on rapidity of fall of leaf of, 87.

,, ,, effectors in pulvinus of, 70(i.

,, ,, electric detection of nervous imjjulse in, 703.

,, ,, ,. response of, 751.

,, evening record of, 63.

INDKX 893

Mimosa piuUca, heliDtiopii- culjuslnu'iit of leaf of. (i{)i».

,, ,, localisation of nervous tissue in, 703.

,, ,. influence of constant electric current on response

of, 92.

,, ,, ,, temperature on response of, 55.

,, ,, Micro-photograph showing nervous tissue in, 702.

,, ,, midday record of, 63.

,, ,, multi[)le response in, 766.

,, ,, petiole-pulvinus preparation of, 75.

,, ,, positive response of. under sub minimal stinudus,

766, 809.

,, ,, positive response of, under sub-tonicity, 682.

,, ,, relative excitabilities of two halves of pulvinus

of, 85.

,, ,, response of abaxial arnl adaxial halves of pul-

vinus of, 736.

,, ,, response of pulvinus of. 36.

„ ,, ,, on stimulation of sub-petioles, 697.

„ ,, ,, to variation of turgor, 39.

,, ,, ,, wireless stimulation. 420.

,, ,, statolithic apparatus in pidvinus of, 715.

,, ,, Recorders for response of, 28.

,, ,, torsional response of, 400, 697.

,, ,, transverse section of pulvinus of. 716.

,, ,, uniform periodic stimulation of. 46.

,, ,, variation of excitability of, after section, 46.

Multiple response, electromotive, 744.

,, ,, mechanical, 766, 780. 784.

,, ,, resistivity, 811.

Mitsa sapienftnn, photo-electric cell of. 837.
Myosotis, localisation of geo-perceptive layer in, 613.

Xadirotropism, 438.
Xastic movements, 547.
Negative curvature, 272.

of tendril. 298.
Negative geotropism, 438.

,, ,, neutralisation and reversal of, 334, 355.

,. ,, of roots. 476.

phototropism. 334.

,, and positive thermonasty, 530.

Neptiniia ohracea, transverse section of pulvinus. 716.
Nerve-and-muscle preparation. 113.

S!)J INDEX

Nerve, direct stimulation in jilant, by pressure of starch grains, 717.
,, indirect ,, ,, ,, ,, 718.

Nervous conduction, laws of variation under electric current, 113
Nervous impulse, contiol of, in animal, 112.

in plant, 109.
,, ,, (It^fmite channel for, 706.

,, ,, reflex in plants, 863.

Nervous tissue, localisation of, 699.
Non-polarisable electrode, 445.
Noon, Light and Thermal, 533.
Nyctitropic Recorder, 537.
Nyctitropism, 523.

,, complexity of, 526.

Xymphni'ii. dim-nal movements of, 549.

,, effect of light on thermonastic movement of, 551.

,, ,, temperature, on thermonastic movement cf,

55 1 .
,, geo-electric response of different layers in lower side,

495.
,, localisation of geo-perceptive layer, 486.

,, negative thermonastic response of, 309, 310.

,, geo-electric distribution across flower stalk, 496.

Oscillating Recorder, 234, 340.
Oscillator. 50.

J\iiiicrnf, charnctoiistic response of. to fi-ansmitted phototropic

excitation, 374.
I'd linijd, diurnal record of leaf, 558.
Para-heli 3tropism, positive and negative, 381.
I'lixslHorn, death-spasm of tendril, 691.

,, rcsjionse of tendril, 33.

,, periods of contraction and recovery, 37.

Periodic movements, causes of, 13.

,, ,, ,, in trees, 15.

Periods of transmission of positive and negative impulses, 139.

,, nuiximum contraction and recovery, 37.

Permeability, variation of, under stimulus, 820.
Petiole-pulvinus-preparation of ^fin>osa, 74.
Pith, electric excitation in, 704.
Phloem, electric excitation in. 703.
/'/iff nix f/arflflff'ifi, 5.
I'hotometiic Recorder, 586.

INDEX 895

'^hotonastic curvatuie, 378.

Phototropic response, after-effect of rise of temperature on, 394.
,, ,, leversal of, under rise of temperature, 393.

,, ,, seasonal change of, 388, 392.

See also Dia-phototropisni,
Phototropic torsion, 398.

,, action of light on, 378.
,, diagrammatic representation of, 399.
,, ,, experimental arrangements for recording,

398.
Photo-geotropic torsional balance, 505.

,, effect of white and red lights on, 506.

,, .. coal gas, 507.

Photic stimulation, effect of unilateral, 280.

,, ,, transmitted effect of, 362.

Phototropism, 313.

,, operative factors in, 314.

Phototropic curve, characteristic of simple, 351.

,, ,, ,, complete, 356.

Phototropic curvature, characteristics of, 347.

,, effect of inci-easing intensity of light, 336.

,, ,, subminimal stimulus, 353.

,, dia- and negative, 314.

,, latent period of, 323.

,, of growing organ, 317, 359.

,, of pulvinated organ, 316, 358.

,, a positive, 314.

Physiological inertia, responsive variation of, on excitability, 68.
Porana paniculata, resistivity variation of, 807.
Positive curvature, 272.
,, impulse, 137, 148.

period of transmission of, 139.
Positive effect, unmasking of, 144.

Positive phototropic curvature, in pulvinated organs, 316.
,, ,, in growing organs, 317.

para-heliotropism of, Eryfhri/ia, 3S2.
radio thermotropism, 412.
geotropism, 438.
thermonasty, 530.
Positive electric responses in subtonic tissues, 810.

to light, 839.
Pulvinus, (Mimoso),

,, action of hydrogen peroxide, on, S8.

896

INDKX

Pulvinus action of l)aiiuin chloride on, 89.

,, ,, characteristic response to geotropic stimulus,

712.
,, ,, copper suh>hate on, 91.

,, ,, tlia-geotropic response of, 722.

effect of amputation of upper half, 82.
,, ,, ,, of lower half, 84.

,, Effectors in, 695.

,, relative sensitiveness of upper and lower halves, 85.

unequal excitability of upper and lower halves to photic^
stimulu!=!, n^O.
Pulvinated organs, effect of ether on, geotropic curvature of, G53.
,, ,, ,, chloroform on, geotropic curvature

of, 656.
„ „ ,, carbon dioxide on, 662.

Poison, contrasted effect of application to root and shoot, 792.
,, effect on growth, 186.
,, Excitatory impulse at death V)y, 781.
Poisonous spray, ineffectiveness of, 791.
Praying Palm, 3.

Quadrant Method of electric i-es|)onse, 814.

,, ,, ,, effect of iiu-reasing inten-

sity of light
on, 818.
,, ,, „ ,, carbon dioxide,

819.
,, ;, ,, chloroform, 819.

Radial organ, geo-electric response of, 725.
Radiograph, Self -Recording, 825.
Radio thermotropism, 410.

Dia- 413.
,, Positive, 412.

Ttaria fiyrina, 125.

Rate of growth, automatic record of, 155.
Ratio of geo-electric excitation and sines of angle of inclination.

456, 634.
Recorder, Geotropic, 427.

for movement of trees, 8.
Oscillating, 33, 340.
,, Nictitropic, 537.

Photometric. 586.

INDRX SU7

Recorder, Resonant. 3-2. 77.

Theimonastic, 309.
Recoverj', effect of constant current on, 9-2.
Red light, effect of, on Mimosa pulvinus. 246.

,, ,, on growth, 210.

Response, comparison of, in growing and non-growin<i. 239.
diverse forms of. 2. 248.

of abaxial and adaxial halves of Mimoxa pulvinus, 736.
of an up-curved organ. 680.
of an inverted organ. 681.
,, of geotropically curved organ, 679.

of petiole of HeUanthus. 740.
,, of subtonic growing organ, 219.

,, positive and negative, 138.

,, Positive, diphasic, and negative electric, 214, 809

,, Positive, under sub-tonicity, 683.

,, Positive under sub-minimal stimulus, 766, 809.

,, reversal of. with reversal of anisotropy, 618.

,, to wireless stimulation, 416.

Response of anisotropic organs, 35.

,, pulvinated organs, 31, 37.

,, to single spark of light, 817.

Resistivity variation, under electric stimulus, 805.
,, ,, mechanical stimulus, 796.

,, ,, Effect of carbon dioxide on, 812.

,, ,, ,, chloroform on, 802, 812.

,, ,, ,, ether on, 812.

,, ,, ,, moderate stimulus on, 808.

,, ,, ,, strong stimulus on, 810.

,, ,, „ sub-minimal stimulus on, 809.

Negative and positive, 810.
Reversal of natural rhythm, 27.
Revival of autonomous pulsation of Desinodiinn, 2il .

growth. 229.
Root, electric response of, 644.

,, electromotive variation between tip and growing region, 473.
,, geo-electric response of, 467.
,, mechanical response to direct stimulus, 462.
,, ,, ,, indirect ,, 463.

Root tip, effect of stimulation of, 465.
,, ,, geo-electric response of, 467.
,, ,, geo-perception at, 474.
Rotation axial, 449.

898 INDEX

Rot<atiou vertical, 458.

i'^cripiis Kijfioor, rate of growth, 159.

,, ,, therniocrescent curve of, 181.

Season, effect of, on excitability, 59.

,, ,, on phototropic curvature, 388, 392.

,, ,, on geo-electric response, 490, 617.

,, ,, on geotropic curvature, 652.

Section, variation of excitability due to, 80.
Selenium cell, 826.

Sensitiveness of Balanced Crescograph, 263.
Sensitive plants, aibitrary distinction of, 676.
Setaria, effect of light at the tip, 368.

,, „ simultaneous stimulation of tiji and hypocotyl,

371.
Shoot, geo-electric excitation of 620.

,, geotropic response of, 442.
Simultaneous electric and mechanical determination of trans-
mission of excitation, 759.
Sinapis, negative phototropism of root of, 376.
Starch-sheath, geo-electric response at, 607.

,, position of, 489.

Spectrum, effect of diffei-ent rays of, on growth, 210.
Statolithic apparatus, in Eclypta, 718.
,, Impatiens, 718.
,, ,, .]/ itiioMd, 717.

Statoliths, theoiy of. 430.

critical angle and, 640.
,, distribution of, in pulvinus and stem, 716, 719.

,, stimulation of nerves by pressure of, 725.

Stimulants, effect of, on growth, 184.

Stimulus, algebraical summation of effects of direct and indirect,
372.
analogy between, of light and gravity, 436.
determination of direction of, 408.
different kinds of, 41.

directive action of, on torsional response, 400.
effect of distance of application of, 138.

,, longitudinal transmission of, on tropic curva-
ture, 271.
transverse tiansmission of, on tropic curva-
ture, 279.
,, unilateral ))hotic, 280.

INDEX 899

Stimulus, effect of unilateral electric, 282.

excitatory effect of, on growing and pulvinated organs,

244.
fashioning conducting path, 757.
inhibitory action of, 295.
laws of effect of direct and indirect, 139.
positive growth response under sub-minimal, 224
summation of geotropic and photic, 436.
Sub-minimal stimulus, effect of, on phototropic curvature, 353.

,, ,, positive response under, 224.

Sub-tonic specimen, action of injury on, 104.
growth response of, 219.
,, ,, positive and negative response in, 147.

,, ,, resistivity variation ui. 810.

Sub-tonicity, modification of response by, 242.
Sunlight, supposed phototropic ineffectiveness of, 333.
Summation of effects of direct and indirect stimulus, 372

of geotropic and phototropic effects, 504.
Susceptibility, 348.

Temperature, after-effect of rise of, on phototropic curvature, 394.
,, irregular fluctuation of, on diurnal curve, 561.

,, effect of, on conduction of excitation, 100, 390.

,, effect on, Desmodium pulsation, 237.

,, ,. dia-geotropic equilibrium, 517.

,, ,, diurnal movement, 27, 539.

,, ,, excitability, 55, 56, 58, 389.

growth, 173.
,, ,, phototropic curvature, 388.

,, ,, thermonastic response, 311.

,, ,, response of Mimosa, 55.

,, .. diurnal curve, 565.

,, maximum for growth, 178.

,. minimum ,, ,, 177.

,, reversal of the phototropic curvature with rise of,

393.
Tendril, anisotropy of, 677.

effect of direct and indirect stimulus on growth of, 293

negative curvature of, 298.

phototropic response of, 390.

relative intensities of response on two sides, 298.

twining of, 288.

!»0() INDKX

Tension, effect of, on growth, 193.

Theorj' of assimilation and dissimilation, 142.

Thermo-geotropism, 509, 530.

diunial movement due to, 554.
'J'heinionastic j)heiH)mena, 21, 305, 546.
,, ,, Law of, 311.

,, ,, effect of theiiiial ladiation on, 308.

,, ,, negative and positive, 21.

Thevmonastic Recorder, 309.

,, response positive and negative, 307.

lesponse, 310.
Time relations of growth resi)onse, 166.
Thermocrescent cviive, 179.

Tiger lily, localisation of geo-perceptive layer of, 613.
Tonic condition, artificial depression of, 145.

,, ,, influence of, on conductivity, 103.

,, ,, ,, on response, 145.

Torsion, complex under light, 403.

,, effect of differential excitability on the direction of, 402.
,, geotropic, 503.
,, i^hototropic, 398.
Torsional balance, 407.
Torsional response, 401.

,, ,, advantage of the method of, 406.

,, ,, balance of phototiopic and geotropic, 505.

,, ,, geotroi)ic, in a and b positions, 504.

„ ,, Laws of, 403.

,, ,, Method of record for, 696.

,, ,, of Hrlin iifliiix petiole, 740.

,, ,, I'ecord of, in Mimosa^ 697.

,, ,, summation of geotropic and phototropic, 504.

,, ,, under geotropic stimulus, 715.

Transmitted excitation, control of, 109.

„ ,, co-ordinated action of, 748.

,, ,, directive action of, 741.

., „ nature of, at death, 781.

complex response of ^fiwo.'<a to, 695.
Transmitted impulse, dual character of, 136.
Transmission of death excitation, 776.
Transmission, longitudinal, 270, 271.

' up-hill ' and ' dowji hill,' 111, 112.
transverse, 270, 27P.
Transjiiration and diuinal movement. 21.

INDEX

901

T ro jxnoJ mn inoju'^, determination of the critical point for geo~
electric excitation, 636.
critical angle for geo-perception, 638.
effect of (^Oj on geotropic curvature of, 660.
,, chloroform ,, ,, 657.

,, ether, 646.
geo-electric response of, 452, 605.
geotropic response of, 433.
localisation of geo-perceptive layer, in petiole-
of, 606, 612, 613.
,, ,, effect of ether on geotropic curvatiii-e of, 654.

Tropic curvature, Laws of, 286.

,, ,, under longitudinal transmission, 271.

,, transverse transmission, 279.
Tropic equilibrium under varying intensities of stimulus, 512.
Tropic movement, 269.

,, ,, anomalies of, 260, 270, 547.

,, ,, under light and its after-effect, 573.

Tube-rose, effect of CO 3 on geo-electric response of upper and
lower sides, 673.
,, geotropic response of, 432.

Turgor, effect of increase on response, 39, 40.
,. variation of, on growth, 188.
,, growth response to negative variation of, 191.
,, ,, ,, positive ,, 190.

,, variation of, under transverse transmission of stimulus,
281.

Ultra-violet light, effect on growth, 211.

,, ,, ,, Miwoxa pulvinus, 247.

Unilateral stimulation, effect of, 280, 281.

,, ,, electric response to, 444.

Universal movements in plants. 11.
Up-change, 143.
Up-hill transmission. 111.
Uricles, geotropic response of, 453.

Vegetable photo-electric cell, 835.

Velocity of conduction in centrifugal and centripetal directions, 99.

,, ,, effect of dessication on, 102.

„ „ ., age on, 101.

,, ,, ,, intensity of stimulus on, 103.

„ „ injury on, 104.

902 INDEX

Velocity of i-oiuluction in effect of temperature on, 100.

,, ,, ,, simultaneous determination of,

759.
Vicia fava, geo-electric resjjonse of root-tip, 470.
Vifis, positive heliotropic response of, 391.

Water-Hyacinth, {Eichomin rrnssipe.s), spread of, 786.

,, methods of destruction, 787.

Weber's law, inadequacy of, 360.
Weight, effect of, on rapidity of responsive fall, 86.
White light, effect of, on Mrniosa jwlvinus, 245.
Wound, effect of on excitability, 76, 484.
,, ,, on growth, 202.

,, reaction, 484.

Wireless stimulation, 416.

,, ,, effect of, on growth, 421.

,, ,, response of Mimosa to, 420.

Xylem, absence of electric excitation in, 703.
Yellow light, effect of on growth, 210.

,, ,, ^fiiiiosn pulvinus, 246.

Zen Mays, Complete phototropic curve of, 359.

Zenithotropism, 438.

Zephera7ithrs, growth rate in peduncle of, 159.

,, thermonastic :ind radio-thermonastic response

of, 308

PRINTKI) AT CALCUTTA BY GANGES I'lUNTING COMPANY, LIMITED.

73
B67

V . 3-4.

Physical &
Applied Sci.
Serials

Bose Research Institute,
Calcutta

Transactions

PLEASE DO NOT REMOVE
CARDS OR SLIPS FROM THIS POCKET

UNIVERSITY OF TORONTO LIBRARY

5T