The Project Gutenberg EBook of Life Movements in Plants, Volume II, 1919, by Sir Jagadis Chunder Bose This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org Title: Life Movements in Plants, Volume II, 1919 Author: Sir Jagadis Chunder Bose Release Date: June 20, 2012 [EBook #40050] Language: English Character set encoding: ISO-8859-1 *** START OF THIS PROJECT GUTENBERG EBOOK LIFE MOVEMENTS IN PLANTS, VOL II *** Produced by Mark C. Orton and the Online Distributed Proofreading Team at http://www.pgdp.net TRANSACTIONS OF THE BOSE RESEARCH INSTITUTE, CALCUTTA, VOL. II, 1919 LIFE MOVEMENTS IN PLANTS BY SIR JAGADIS CHUNDER BOSE, Kt., M.A., D.Sc., C.S.I., C.I.E., PROFESSOR EMERITUS, PRESIDENCY COLLEGE, DIRECTOR, BOSE RESEARCH INSTITUTE, WITH 128 ILLUSTRATIONS CALCUTTA BENGAL GOVERNMENT PRESS 1919 PUBLISHED BY THE BOSE RESEARCH INSTITUTE, CALCUTTA. WORKS BY THE SAME AUTHOR. RESPONSE IN THE LIVING AND NON-LIVING. With 117 Illustrations, 8vo. 10s. 6d. 1902 PLANT RESPONSE: AS A MEANS OF PHYSIOLOGICAL INVESTIGATION. With 278 Illustrations, 8vo. 21s. 1906 COMPARATIVE ELECTRO-PHYSIOLOGY. A PHYSICO-PHYSIOLOGICAL STUDY. With 406 Illustrations, 8vo. 15s. 1907 RESEARCHES ON IRRITABILITY OF PLANTS. With 190 Illustrations, 8vo. 10s. 6d. net 1913 LIFE MOVEMENTS IN PLANTS, VOL. I. With 92 Illustrations, 8vo. 10s. 6d. 1918 Longmans, Green & Co. London, New York, Bombay and Calcutta. PREFACE TO VOLUME II. I have in the present volume dealt with the intricate phenomena of different tropisms. The movements in plants under the stimuli of the environment—the twining of tendrils, the effect of temperature, the action of light inducing movements sometimes towards and at other times away from the stimulus, the diametrically opposite responses of the shoot and the root to the same stimulus of gravity, the day and night positions of organs of plants—these, and many others present such diversities that it must have appeared a hopeless endeavour to discover any fundamental reaction [i] applicable in all cases. It has therefore been customary to assume different sensibilities especially evolved for the advantage of the plant. But teleological argument and the use of descriptive phrases, like positive and negative tropism, offer no real explanation of the phenomena. Thus to quote Pfeffer "When we say that an organ curves towards a source of illumination, because of its heliotropic irritability we are simply expressing an ascertained fact in a conveniently abbreviated form, without explaining why such curvature is possible or how it is produced.... Many observers have unfortunately devoted their attention to artificially classifying the phenomenon observed, and have entirely neglected the explanation of causes underlying them." He also adds that in regard to the phenomenon of growth and its variations, an empirical treatment is all that is possible in the present state of our knowledge; but deduction from results of experimental investigation "still remains the ideal of physiology, and only when this ideal has been attained, shall we be able to obtain a comprehensive view of the interacting factors at work in the living organism." In my previous work on "Plant Response" (1906) I described detailed investigations on irritability of plants which I carried out with highly sensitive recorders. The plant was thus made to tell its own story by means of its self-made records. The results showed that there is no specific difference in physiological reaction of different organs to justify the assumption of positive and negative irritabilities. A generalisation was obtained which gave a complete explanation of diverse movements in plants. The results were fully confirmed by an independent method of inquiry, namely that of electric response, which I have been able to elaborate so as to become a very important means of research. The investigations described in the present volume not only support the conclusions reached in my earlier works, but have led to important additions. It is evident that the range of our investigation is limited only by our power of recording the rate of plant-movement, that is to say, in the measurement of length and time. In these respects the instruments that I have been able to devise have surpassed my sanguine expectations. The Resonant Recorder traces time-intervals as short as a thousandth part of a second, while my Balanced Crescograph enables us to measure variation of rate of growth as minute as 1⁄1000 millionth of an inch per second, the sensitiveness of this apparatus thus rivals that of the spectroscope. The increasing refinement in our experimental methods cannot but lead to important advances towards a deeper understanding of underlying reactions in the living organism. I shall here draw attention to only a few of the important results given in the present volume. The tropic effect of light has been shown to have a definite relation to the quantity of incident light. A complete tropic curve has been obtained from sub-minimal to maximal stimulation which shows the inadequacy of Weber's law, for the sub-minimal stimulus induces a qualitative difference in physiological reaction. It has further been shown that the prevalent idea that perception and heliotropic excitation are two distinct phenomena is without any foundation. With reference to the effect of ether waves on plants, I have given an account of my discovery of the response of all plants to wireless stimulation, the results being similar to that induced by visible light. The perceptive range of the plant is thus infinitely greater than ours; for it not only perceives, but also responds to different rays of the vast ethereal spectrum. The results obtained by the method of geo-electric response show that the responsive reaction of the root is in no way different from that of the shoot, the opposite movements being due to the fact that in the shoot the stimulation is direct, and in the root it is indirect. Full description is given of the new method of physiological exploration by means of the electric probe, by which the particular layer which perceives the stimulus of gravity is definitely localised. The method of electric probe is also found to be of extended application in the detection of physiological changes in the interior of an organ. An important factor of nyctitropic movements, hitherto unsuspected, is the effect of variation of temperature on geotropic curvature. This and other co-operative factors have been fully analysed, and a satisfactory explanation has been offered of various types of diurnal movement. A generalisation has been obtained which explains all the diverse movements of plants, under all modes of stimulation: it has been shown that direct stimulation induces contraction and retardation of growth, and that indirect stimulation induces an expansion and acceleration of growth. Another generalisation of still greater importance is the establishment of identical nature of physiological reaction in the plant and the animal, leading to advances in general physiology. Thus the discovery of a method for immediate enhancement or inhibition of nervous impulse in the plant led to my success in the control of nervous impulse in the animal. Another important discovery was the dual nervous impulses in plants, and I have very recently been able to establish, that the nervous impulse generated in the animal nerve by stimulus is not single, but double. The study of the responsive phenomena in plants must thus form an integral part of physiological investigation into various problems relating to the irritability of all living tissues, and without such study the investigation must in future remain incomplete. J. C. BOSE. October 1919. CONTENTS. PART III. TROPISM IN PLANTS. PAGE. XXII.—THE BALANCED CRESCOGRAPH. Principle of the Method of Balance—Compensating movement—Growth-scale—Sensitiveness of the Crescographic Balance —Effect of CO2—Effect of anæsthetics 255 XXIII.—ON TROPIC MOVEMENTS. Complexity of the problem—Contradictory nature of responses—Two classes of tropic responses—Longitudinal transmission of effect of stimulus—Transverse transmission of effect of stimulus—Modification of tropic curvature by conducting power of tissues and differential excitability of the organ 268 XXIV.—TROPIC CURVATURE WITH LONGITUDINAL TRANSMISSION OF EFFECT OF STIMULUS. Dual impulses, positive and negative, caused by stimulus—Direct and Indirect stimulus—Tropic effect of Indirect stimulation 271 XXV.—TROPIC CURVATURE WITH TRANSVERSE TRANSMISSION OF EFFECT OF STIMULUS. [ii] [iii] [iv] [v] [vi] [Pg i] [Pg ii] Turgor variation under transverse transmission of stimulus-effect—Tropic responses of pulvinated and growing organs to unilateral stimulation—Direct unilateral stimulation—Indirect unilateral stimulation—Difference of effects induced by Direct and Indirect stimulation—Laws of tropic curvature 279 XXVI.—MECHANOTROPISM: TWINING OF TENDRILS. Anomalies of mechanotropism—Effects of indirect and direct electric stimulation on growth of tendril—Effect of direct and indirect mechanical stimulus—Immediate and after-effect of stimulus—Inhibitory action of stimulus—Response of less excitable side of the tendril—Relative intensities of responses of upper and under sides of tendril of Passiflora—Negative curvature of tendril 288 XXVII.—ON GALVANOTROPISM. Polar effects of electric current on growth—Effect of anode and cathode on growth 301 XXVIII.—ON THERMONASTIC PHENOMENA. Effect of temperature—Different thermonastic organs—Two types of response: Positive and Negative—Effect of rise of temperature and of stimulus on thermonastic organs—Law of thermonastic reaction 305 XXIX.—ON PHOTOTROPISM. Complexity of problem of phototropic reaction—Action of light—Positive phototropic curvature of pulvinated organs—Positive phototropic curvature of growing organs—Phenomenon of recovery—Immediate and after-effect of light on growth—Latent period of phototropic reaction—Growth variation induced by flash of light from a single spark—Maximum positive curvature under continued action of light 313 XXX.—DIA-PHOTOTROPISM AND NEGATIVE PHOTOTROPISM. Differential excitability of two halves of pulvinus of Mimosa—Transformation of positive to negative curvature—Tropic effect under sunlight—Negative phototropism of shoot and root 328 XXXI.—RELATION BETWEEN THE QUANTITY OF LIGHT AND THE INDUCED PHOTOTROPIC CURVATURE. Effect of increasing intensity of light on pulvinated and growing organs—Effect of increasing angle—Effect of duration of exposure 338 XXXII.—THE PHOTOTROPIC CURVE AND ITS CHARACTERISTICS. Summation of stimulus—General consideration—The general characteristic curve—Characteristics of simple phototropic curve —Variation of susceptibility for excitation in different parts of the curve—Effect of sub-minimal stimulus—The complete phototropic curves of pulvinated and growing organs—Limitation of Weber's law 346 XXXIII.—TRANSMITTED EFFECT OF PHOTIC STIMULATION. Effect of light applied on tip of Setaria—Response of growing region to unilateral stimulus—Effect of simultaneous stimulation of the tip and the hypocotyl—Algebraical summation of effects of direct and indirect stimuli 362 XXXIV.—ON PHOTONASTIC CURVATURES. Phototropic response of anisotropic organs—Positive para-heliotropism—Negative para-heliotropism—Responses of pulvinated and growing organs to light 378 XXXV.—EFFECT OF TEMPERATURE ON PHOTOTROPIC CURVATURE. Effect of temperature on excitability—Effect of temperature on conduction—Phototropic response of tendrils—Seasonal variation of phototropic curvature—Antagonistic effects of light and of rise of temperature 388 XXXVI.—ON PHOTOTROPIC TORSION. Torsional response to light—Effect of different modes of lateral stimulation—Effect of differential excitability on the direction of torsion—Laws of torsional response—Complex torsion under light—Advantages of the Method of Torsional Response— The Torsional Balance—Determination of the direction of stimulus 397 XXXVII.—RADIO-THERMOTROPISM. Effect of infra-red radiation—Positive radio-thermotropism—Dia-radio-thermotropism—Negative radio-thermotropism 410 XXXVIII.—RESPONSE OF PLANTS TO WIRELESS STIMULATION. Effects of different rays of spectrum on growth—The wireless system—Mechanical and electrical responses of Mimosa to Hertzian waves—Effect of wireless stimulation on growth of plants 416 XXXIX.—GEOTROPISM. [Pg iii] [Pg iv] [Pg v] Direction of the stimulus of gravity—The Geotropic Recorder—Determination of the character of geotropic reaction—Theory of statoliths—Determination of the latent period—The complete geotropic curve—Determination of effective direction of stimulus of gravity—Algebraical summation of effects of geotropic and photic stimulus—Analogy between the effects of stimulus of light and of gravity—Relation between the directive angle and geotropic reaction—Differential geotropic excitability 425 XL.—GEO-ELECTRIC RESPONSE OF SHOOT. Electric response to direct and indirect stimulation—Experimental arrangement for obtaining geo-electric response—Geo- electric response of the upper and lower sides of the organ—Method of Axial Rotation—Characteristics of geo-electric response—Physiological character of geo-electric response—Effect of differential excitability of the organ—Law determining the relation between angle of inclination and geotropic effect—Method of Vertical Rotation—Electric response through an entire cycle—Relation between angle of vertical rotation and intensity of geo-tropic reaction 442 XLI.—MECHANICAL AND ELECTRICAL RESPONSE OF ROOT TO VARIOUS STIMULI. Mechanical and electrical response to Direct stimulation—Mechanical and electrical response to Indirect stimulation—Effect of unilateral stimulation applied at the root-tip 461 XLII.—GEO-ELECTRIC RESPONSE OF ROOT. Geo-electric response of the root-tip—Electric response in the growing region of root—Differential effect between the tip and the growing region—Geo-perception at the root-tip 467 XLIII.—LOCALISATION OF GEO-PERCEPTIVE LAYER BY MEANS OF THE ELECTRIC PROBE. Principle of the method of electric exploration—The Electric Probe—Electric exploration of the geo-perceptive layer—Geo- electric reaction at different depths of tissues—Microscopical examination of the maximally excited layer—Influence of season on geo-electric response—Tests of insensitive specimens—Reaction at lower side of the organ—The Method of Transverse Perforation 478 XLIV.—ON GEOTROPIC TORSION. Arrangement for torsional response—Algebraical summation of geotropic, and phototropic effects—Balance of geotropic by phototropic action—Comparative balancing effects of white and red lights—Effect of coal gas on photo-geotropic balance 503 XLV.—ON THERMO-GEOTROPISM. Necessary conditions for geotropic curvature—Modifying influence of temperature on geotropic curvature—Magnetic analogue —Tropic equilibrium under varying intensities of stimulus—Effect of variation of temperature on geotropic torsion—Variation of apo-geotropic curvature under thermal change—Effect of variation of temperature on dia-geotropic equilibrium 509 PART IV. NIGHT AND DAY MOVEMENTS IN PLANTS. XLVI.—DIURNAL MOVEMENTS IN PLANTS. Complexity of the problem—The different factors involved—Autonomous movements—Epinasty and hyponasty—Positive and negative thermonasty—Thermo-geotropism—Classification of diurnal movements—Discriminating tests for classification— Diurnal variation of light and of temperature 523 XLVII.—DIURNAL MOVEMENT DUE TO ALTERNATION OF LIGHT AND DARKNESS. Experimental arrangements—The Quadruplex Nyctitropic Recorder—Diurnal movement of the leaflet of Cassia alata—Effect of variation of temperature—Effect of variation of light—Diurnal movement of the terminal leaflet of Desmodium gyrans— The 'midday sleep' 535 XLVIII.—DIURNAL MOVEMENT DUE TO VARIATION OF TEMPERATURE AFFECTING GROWTH. Tropic and nastic movements—Distinction between thermonastic and thermo-geotropic action—Diurnal movement of Nymphæa—Action of light—Effect of variation of temperature 546 XLIX.—DAILY MOVEMENT IN PLANTS DUE TO THERMO-GEOTROPISM. Characteristics of thermo-geotropic movements—Diurnal movement of Palm trees—Diurnal movement of procumbent stems and of leaves—Continuous diurnal record for successive thermal noon—Modification of the diurnal curve—Effect of fluctuation of temperature—Effect of restricted pliability of the organ—Effect of age—Effect of season—Reversal of the normal rhythm—Effect of constant temperature—Diurnal movement in inverted position 554 L.—THE AFTER-EFFECT OF LIGHT. Electric after-effect of light—After-effect at pre-maximum, maximum, and post-maximum—Tropic response under light, and its after-effects at pre-maximum, maximum, and post-maximum 569 LI.—THE DIURNAL MOVEMENT OF THE LEAF OF MIMOSA. [Pg vi] [Pg vii] [Pg viii] Four different phases in the diurnal record of Mimosa—Different factors determining its diurnal movement—Diurnal variation of geotropic torsion—Autonomous pulsation of the leaf of Mimosa—The Photometric Recorder—Effect of direct light—The evening spasmodic fall of the leaf—Diurnal movement of the amputated petiole—Diurnal curve of the petiole of Cassia alata—Response of Mimosa to darkness at different parts of the day—After-effect of light at pre-maximum, maximum, and post-maximum 576 ILLUSTRATIONS. FIGURE. PAGE. 93. Arrangement for compensation of growth-movement by equal subsidence of plant-holder 257 94. Photograph of the Balanced Crescograph 258 95. Balanced Crescographic record 260 96. Record showing the effect of CO2 265 97. Effect of ether and of chloroform 266 98. Diagrammatic representation of effects of Indirect and Direct stimulation 275 99. Tropic curvature of Crinum 276 100. Turgor variation caused by Indirect stimulation 281 101. Response of Mimosa leaf under transverse transmission of effect of electric stimulus 282 102. Diagrammatic representation of Indirect and Direct stimulation of tendril 290 103. Record by Method of Balance 291 104. Variation of growth under direct stimulation 292 105. Positive curvature of tendril of Cucurbita 295 106. Diagrammatic representation of effects of Indirect and Direct unilateral stimulation of tendril 296 107. Retardation of rate of growth under cathode 303 108. Acceleration of rate of growth under anode 303 109. Thermonastic and radionastic responses of petal of Zephyranthes 308 110. The Thermonastic Recorder 309 111. Negative thermonastic response of Nymphæa 310 112. Successive positive responses of the terminal leaflet of bean plant 317 113. Positive response and recovery under moderate phototropic stimulation 318 114. Persistent positive curvature under stronger stimulation 318 115. Immediate and after-effect of stimulus of light on growth 320 116. Latent period for photic stimulation 324 117. Effect of a single electric spark on growth 325 118. Responses of Mimosa leaf to light from above 330 119. Responses of Mimosa leaf to light from below 330 120. Record of effect of continuous application of light on upper half of pulvinus of Mimosa 331 121. Positive and negative phototropic response of Oryza 335 122. Leaf of Desmodium gyrans 339 123. The Oscillating Recorder 340 124. Tropic effect of increasing intensity of light on the leaflet of Desmodium gyrans 341 125. Tropic effect of increasing intensity of light on growing organ (Crinum) 341 126. The Collimator 342 127. Effect of angle of inclination of light on tropic curvature of pulvinated organ 343 128. Effect of angle of inclination on growth-curvature 343 129. Effect of increasing duration of exposure to light 344 130. Effect of continuous electric and photic stimulation on rate of growth 348 131. Characteristic curve of iron 351 132. Simple characteristic curve of phototropic reaction 351 133. Complete phototropic curve of pulvinated organ 358 134. Complete phototropic curve of growing organ 359 135. Arrangement for local application of light 367 136. Response of seedling of Setaria to light 368 137. Effect of application of light to the growing hypocotyl of Setaria 370 138. Response to direct and indirect photic stimulus 373 139. Diagrammatic representation of the effects of direct and indirect stimulation of Setaria 375 [Pg ix] [Pg x] 140. Photonastic curvature of creeping stem of Mimosa pudica 380 141. Positive phototropic response of Erythrina indica 382 142. Response of leaflet of Mimosa to light 383 143. Response of leaflet of Averrhoa to light 383 144. Diagrammatic representation of different types of phototropic response 384 145. Phototropic curvature of tendril of Passiflora 392 146. Effect of rise of temperature on phototropic curvature 394 147. After-effect of rise of temperature 395 148. Arrangement for record of torsional response 399 149. Record of torsional response of pulvinus of Mimosa pudica 400 150. Leaflets of Cassia alata 404 151. Positive response to thermal radiation 413 152. Record of positive, neutral, and reversed negative curvature under thermal radiation 414 153. Diagrammatic representation of the wireless system 419 154. Mechanical response of Mimosa leaf to electric waves 420 155. Electric response of Mimosa to Hertzian wave 420 156. Record of responses of growing organs to wireless stimulation 422 157. The Quadruplex Geotropic Recorder 428 158. Effect of alternate application of cold on upper and lower sides of the organ 430 159. Geotropic response of flower stalk of Tube-rose 433 160. Geotropic response of Tropæolum 433 161. The Complete Geotropic Curve 435 162. Diagrammatic representation of photic and geotropic stimulation 436 163. The effect of super-imposition of photic stimulus 436 164. Diagrammatic representation of the mechanical and electrical response 443 165. Diagrammatic representation of geo-electric response 447 166. Diagrammatic representation of Methods of Axial and Vertical Rotation 449 167. Diagrammatic representation of the geo-electric response of the shoot 450 168. Geo-electric response of the petiole of Tropæolum 452 169. Geo-electric response of the scape of Uriclis 453 170. Mechanical and electric response to indirect stimulation 463 171. Diagrammatic representation of mechanical and electric response of root 464 172. Diagrammatic representation of geo-electric response of root-tip 469 173. Diagrammatic representation of geo-electric response of growing region of root 471 174. Diagrammatic representation of the geo-perceptive layer 480 175. The Electric Probe 483 176. Transverse section showing continuous geo-perceptive layer (Bryophyllum) 488 177. Curve of geo-electric excitation in different layers of Nymphæa 497 178. Curve of geo-electric excitation in Bryophyllum 497 179. Diagram of arrangement of geotropic torsional response 503 180. Additive effect of stimulus of gravity and light 505 181. Algebraical summation of geotropic and phototropic actions 505 182. Comparative balancing effects of white and red lights 506 183. Effect of coal gas on photo-geotropic balance 507 184. Diagram of magnetic balance 511 185. Effect of variation of light on phototropic equilibrium 512 186. Effect of variation of temperature on geotropic torsion 514 187. Simultaneous records of variation of temperature, on up and down movement, and of torsion of the leaf of Mimosa 518 188. Arrest of pulsatory movement of leaflet of Desmodium gyrans by light 528 189. Effect of unilateral light on hyponastic movement 529 190. The Nyctitropic Recorder 537 191. Effect of sudden darkness on leaflet of Casia alata 539 192. Diurnal movement of the leaflet of Cassia alata 540 193. The day and night position of the petiole and terminal leaflet of Desmodium gyrans 541 194. Diurnal record of the terminal leaflet of Desmodium gyrans 542 195. Photograph of closed flower of Nymphæa during day 550 196. Photograph of open flower of Nymphæa at night 550 [Pg xi] [Pg xii] [Pg xiii] 197. Action of light on the petal of Nymphæa 551 198. Diurnal movement of the petal of Nymphæa 552 199. Diurnal record of the Sijbaria Palm 556 200. Diurnal record of inclined Palm, geotropically curved procumbent stem of Tropæolum, and dia-geotropic leaf of Palm 557 201. Diurnal record of leaves of Dahlia, Papya, and Croton 558 202. Diurnal record of procumbent stem of Tropæolum, and leaf of Dahlia for two successive days 560 203. Abolition of the diurnal movement under constant temperature (Tropæolum) 565 204. Effect of inversion of plant on diurnal movement of Tropæolum 567 205. Electric response of the leaf stalk of Bryophyllum under light 571 206. Diagrammatic representation of electric after-effect of photic stimulation 571 207. After-effect of pre-maximum photic stimulation 574 208. After-effect of maximum photic stimulation 574 209. After-effect of post-maximum photic stimulation 574 210. Diurnal record of Mimosa in summer and winter 577 211. Record of diurnal variation of torsion in Mimosa leaf 582 212. Continuous record of automatic pulsation of Mimosa leaf 585 213. Photometric record showing variation of intensity of light from morning to evening 586 214. Record of leaf of Mimosa after amputation of sub-petioles 589 215. Diurnal record of Cassia leaf 591 216. Post-maximum after-effect of light on response of leaflet of Cassia 592 217. Effect of periodic alternation of light and darkness on response of Mimosa leaf 594 218. Pre-maximum after-effect of light in Mimosa 595 219. After-effect at maximum 595 220. Post-maximum after-effect exhibiting over-shooting below position of equilibrium 595 PART III. TROPISM IN PLANTS. XXII.—THE BALANCED CRESCOGRAPH By Sir J. C. Bose. We shall in the succeeding series of papers deal with the subject of tropism in general. Different plant organs undergo curvature or bending, sometimes towards and at other times away from the stimulus which induces it. The problem is very intricate; the possibility of its solution will depend greatly on the accurate determination of the immediate and after-effects of various stimuli on the responding organ. The curvature induced in the growing organ is brought about by variation, often extremely slight, of the rate of growth; the result, moreover, is liable to be modified by the duration and point of application of stimulus. The difficulties connected with the problem can only be removed by the detection and measurement of the minutest variation in growth, and by securing a continuous and automatic record of the entire history of the change. In the chapter on High Magnification Crescograph an account is given of the apparatus which I have devised by which the rate of growth may be magnified from ten thousand to ten millions times. It is thus possible to measure the imperceptible growth of plants for a period shorter than a single second. The variation of normal rate of growth is also found by measuring successive growth records on a stationary plate at regular intervals, say of ten seconds, or from the flexure in the growth-curve taken on a moving plate (p. 163). I was next desirous of exalting the sensitiveness to a still higher degree by an independent method, which would not only reveal very slight variation induced in the rate of growth, but also the latent period and time-relations of the change. For this purpose I at first devised the Optical Method of Balance[1] which was considered at the time to be extremely sensitive. The spot of light from the Optical Lever (which magnified the rate of growth) was made to fall upon a mirror to which a compensating movement was imparted so that the light-spot after double reflection remained stationary. Any change of rate of growth—acceleration or retardation—was at once detected by the movement of the hitherto stationary spot of light in one direction or the other. A very careful manipulation was required for the adjustment of the Optical Balance; the record moreover was not automatic. For these reasons I have been engaged for several years past in perfecting a new apparatus by which, (1) the balance could be directly obtained with the utmost exactitude, (2) where an attached scale would indicate the exact rate of growth, and (3) in which the upsetting of the balance by external stimulus would be automatically recorded, the curve giving the time relations of the change. PRINCIPLE OF THE METHOD OF BALANCE. I shall take a concrete example in explanation of the method of balance. Taking the rate of growth per second of a plant to be 1⁄50,000 inch or 0·5 µ, per second (equal to the wave length of sodium light), the tip of the plant will be maintained at the same point in space if we succeeded in making the plant-holder subside exactly at the same rate. The growth-elongation of the plant will then be exactly balanced by a compensating movement downwards. The state of exact balance is indicated when the recording lever of the Crescograph traces a horizontal line on the moving plate. [Pg xiv] [Pg 253] [Pg 254] [Pg 255] [Pg 256] [Pg 257] Overbalance or underbalance will deflect the record below or above the horizontal line. Fig. 93. Fig. 93.—Arrangement for compensation of growth-movement by equal subsidence of plant-holder; S, adjusting screw for regulation of speed of rotation; G, governor; W, heavy weight; P, plant-holder. COMPENSATING MOVEMENT. For securing exact balance the holder of the plant P, in the given example, will have to subside at a rate of 1⁄50,000 inch per second. This is accomplished by a system of reducing worm and pinion, also of clock wheels (Fig. 93). The clock at first used for this purpose was worked by the usual balance wheel. Though this secured an average balance yet as each tick of the clock consisted of sudden movement and stoppage, it caused minute variation in the rate of subsidence; this became magnified by the Crescograph and appeared as a series of oscillations about a mean position of equilibrium. This particular defect was obviated by the substitution of a fan governor for the balance wheel. But the speed of rotation slows down with the unwinding of the main spring, and the balance obtained at the beginning was found to be insufficient later on. The difficulty was finally overcome by the use of a heavy weight W, in the place of coiled spring. The complete apparatus is seen in figure 94. Fig. 94. Fig. 94.—Photographic reproduction of the Balanced Crescograph. L, L', magnifying compound lever. R, recording plate. P, plant. C, clock work for oscillation of the plate and lateral movement. G, governor. M, circular growth-scale. V, plant-chamber. For purpose of simplicity of explanation, I assumed the growth rate to have a definite value of 1⁄50,000 inch per second. But the rate varies widely in different plants and even in the same plant at different days and seasons. In practice the rate of growth for which compensation has to be made varies from 1⁄150,000 to 1⁄25,000 inch, or from 0·17 µ to 1·0 µ per second. We have thus to secure some means of continuous adjustment for growth, the rate of which could be continuously varied from one to six times. This range of adjustment I have been able to secure by the compound method of frictional resistance and of centrifugal governor. As regards frictional resistance the two pointed ends of a hinged fork rub against a horizontal [Pg 258] [Pg 259] circular plate not shown in the figure. By means of the screw head S, the free ends of the fork spread out and the circumference of the frictional circle continuously increased. The centrifugal governor is also spread out by the action of the adjusting screw. By the joint actions of the frictional control and the centrifugal governor, the speed of rotation can be continuously adjusted from 1 to 6 times. When the adjusting screw is set in a particular position, the speed of rotation, and therefore the rate of subsidence of plant-holder, remains absolutely constant for several hours. The attainment of this constancy is a matter of fundamental importance, and it was only by the employment or the compound system of regulation that I was able to secure it. The method of obtaining balance now becomes extremely simple. Before starting the balancing movement by clock regulation, the plant is made to record its magnified growth by the Crescograph. The compensation is effected as follows: the speed of the clockwork is at the beginning adjusted at its lowest value, and the pressure of a button starts the balancing movement of the plant downwards. On account of partial balance the record will be found to be less steep than before; the speed of the clock is gradually increased till the record becomes perfectly horizontal under exact balance. Overbalance makes the record slope downwards. In figure 95 is seen records of underbalance (a) and overbalance (b), to the extent of about 3 per cent. Fig. 95. Fig. 95.—Balanced Crescographic record: (a) showing effect of underbalance and (b) overbalance of about 3 per cent. (Magnification 2,000 times.) It will thus be seen that the effect of an external agent may be detected by the upsetting of the balance; an up-movement indicates (unless stated to the contrary) an enhancement of the rate of growth above the normal; and a down-movement, on the other hand, a depression of the normal rate. Calibration.—The calibration of the instrument is obtained in two different ways. The rate of subsidence of the plant-holder, by which the balance is obtained, is strictly proportional to the rate of rotation of the vertical spindle and the attached train of clock-wheels. A striker is attached to one of the wheels, and a bell is struck at each complete revolution. The clockwork is adjusted at a medium speed, the bell striking 35 times in a minute. A microscope micrometer is focussed on a mark made on the plant-holder, and the amount of subsidence of the mark determined after one minute; this was found to be 0·0525 mm. As this fall occurred after 35 strokes of the bell the subsidence per stroke was 0·0015 mm. Determination of the absolute rate of growth.—If growth be found balanced at N strokes of bell per minute, the rate of subsidence per second = N × ·0015⁄60 mm. per second = N × ·000025 mm. per second = N × ·025 µ per second = N × 10-5 inch per second. Example.—The growth of a specimen of Zea Mays was found balanced when the number of strokes of the bell was 20 times in a minute. Absolute rate of growth = 20 × ·025 µ = 0·5 µ per second or = 20 × 10-5 inch " or = 1⁄50,000 " " If we take the wave length of sodium light λ as our standard, the growth in length per second is equal to λ. This will give us some idea of the sensitiveness of the Crescograph employed in recording the movement of growth. GROWTH-SCALE. The Balanced Crescograph enables us not merely to determine the absolute rate of growth, but the slightest fluctuation in that rate. Indicator Scale.—All necessity of calculation is obviated by the scale provided with the apparatus. The speed of clockwork which brings about the balance of growth is determined by the position of the adjusting screw S, the gradual lowering of which produces a continuous diminution of speed. A particular position of the screw therefore indicates a definite rate of subsidence for balancing growth. By a simple mechanism the up or down movement of the screw causes rotation of an index pivoted at the centre of a circular scale. Each division of the scale is calibrated by counting the corresponding number of strokes of the bell per minute at different positions of the adjusting screw. The scale is calibrated in this manner to indicate different rates of growth from 0·2 µ to 1·2 µ per second. The determination of the rate of growth now becomes extremely simple. Few turns of the screw bring about the balance of growth and the resulting position of the index against the circular scale automatically indicates the absolute rate. The procedure is even simpler and more expeditious than the determination of the weight of a substance by means of a balance. SENSITIVENESS OF THE CRESCOGRAPHIC BALANCE. [Pg 260] [Pg 261] [Pg 262] Perhaps the most delicate method of measuring lengths is that afforded indirectly by the spectrum of a light. A good spectroscope resolves differences of wave lengths of D1 (= 0·5896 µ) and D2 (= 0·5890) i.e. of 1 part in a thousand. The average rate of growth of Zea Mays is of this order; being about 0·5 µ per second. Let us consider the question of the possibility of detecting a fractional variation of the ultra-microscopic length by means of the Balanced Crescograph. In reality the problem before us is more intricate than simple measurement of change of length; for we have to determine the rate of variation of length. The sensitiveness of the balance will, it is obvious, depend on the magnifying power of the Crescograph. By the Method of Magnetic Amplification referred to in page 170, I have succeeded in obtaining a magnification of ten million times. In this method a very delicate astatic system of magnets undergoes deflection by the movement of a magnetised lever in its neighbourhood. A spot of light reflected from a small mirror attached to the astatic system, thus gives the highly magnified movement of the rate of growth, which may easily be raised to ten million times. I shall in the following describe the results obtained with this easily managed magnification of ten million times. Determination of sensitiveness: Experiment 99.—A seedling of Zea Mays was placed on the Crescographic Balance; and the magnetic amplification, as stated above, was ten million times. With 18 strokes of the bell per minute the spot of light had a drift of + 266 cm. per minute to the right; this is because the growth was underbalanced. With faster rate of clock movement, i.e., 21 strokes in 68 seconds or 18·53 strokes per minute, the drift of the spot of light, owing to overbalance, was to the left at the rate of - 530 cm. per minute. Thus (1) 18 strokes per minute caused a drift of + 266 cm. per minute. (2) 18·53 strokes per minute caused a drift of - 530 cm. per minute. Hence by interpolation the exact balance is found to correspond to 18·177 strokes per minute. Therefore the absolute rate of growth = 18·177 × 0·025 µ per second. = 0·45 µ per second. = 0·000018 inch per second. We learn further from (1) and (2) that a variation of (18·53 - 18)⁄18·177 produces a change of drift of the spot of light from + 266 to - 530 cm., i.e., of 796 cm. per minute. As it is easy to detect a drift of 1 cm. per minute a variation of 0·53⁄(18·177 × 796), or 1 part in 27,000 may thus be detected by the Method of Balance. The spectroscopic method enabled us, as we saw, to detect change of wave length 1 part in a thousand. The sensibility of the Balanced Crescograph is thus seen to rival, if not surpass that of the spectroscope. For obtaining a general idea of the sensitiveness, the absolute of growth in the instance given above was 0·00018 inch per second, and the Balanced Crescograph was shown capable of discriminating a variation of 1 part in 27,000; hence it is possible to detect by this means a variation of 1⁄1,500 millionth of an inch per second. This method of unprecedented delicacy opens out a new field of investigation on the effect of changes of environment in modification of growth; instances of this will be found in subsequent chapters. I give below accounts of certain demonstrations which will no doubt appear as very striking. After obtaining the exact balance a match was struck in the neighbourhood of the plant. This produced a marked movement of the hitherto quiescent spot of light, thus indicating the perception of such an extremely feeble stimulus by the plant. Breathing on the plant causes an enhancement of growth due to the joint effects of warmth and carbonic acid gas. A more striking experiment is to fill a small jar with carbonic acid and empty it over the plant. A violent movement of the spot of light to the right demonstrates the stimulating effect of this gas on growth. The method described above is excessively sensitive; for general purposes and for the method of direct record, a less sensitive arrangement is sufficient. I give below accounts of several typical experiments in which the recording form of Crescograph was employed, the magnification being only 2,000 times. Fig. 96. Fig. 96.—Record showing the effect of CO2. Horizontal line at beginning indicates balanced growth. Application of CO2 at arrow induces enhancement of growth shown by the up-curve followed by depression, shown by the down-curve. Successive dots at intervals of 10 seconds. (Seedling of wheat.) Effect of carbonic acid on Balanced growth: Experiment 100.—I have already shown that carbonic acid diluted with air induces an enhancement of the rate of growth, but its long continued action induces a depression (p. 185). I shall now employ the Method of Balance in studying the effect of CO2 on growth. It should be remembered in this connection that the horizontal record indicates the balance of normal rate of [Pg 263] [Pg 264] [Pg 265] growth. An up-curve exhibits the induced enhancement and a down-curve, a depression of growth. In the present experiment after obtaining the exact balance, pure carbonic acid gas was made to fill up the plant-chamber at the point marked with an arrow (Fig. 96). It will be seen that this induced an almost immediate acceleration of the rate, the latent period being less than five seconds. The acceleration continued for two and half minutes; the accelerated rate then slowed down, became enfeebled, and the growth returned for a short time to the normal as indicated by the horizontal portion at the top of the record; this proved to be the turning point of inversion from acceleration into retardation of growth. The stronger is the concentration of the gas the earlier is the point of inversion. With diluted carbonic acid the acceleration may persist for an hour or more. EFFECT OF ANÆSTHETICS. Effect of Ether: Experiment 101.—Dilute vapour of ether is found to induce an acceleration of rate of growth which persist for a considerable length of time. This is seen in the upsetting of the balance upwards on the introduction of the vapour (Fig. 97a.). Fig. 97. Fig. 97.—(a) Effect of ether, acceleration of growth, (b) effect of chloroform preliminary acceleration followed by depression. Effect of Chloroform: Experiment 102.—The effect of chloroform vapour is relatively more depressing than ether. Application of chloroform is seen to induce at first an acceleration which persisted for 50 seconds, but after this depression set in (Fig. 97b). Prolonged application of the anæsthetic is followed by the death of the plant. SUMMARY. In the Method of Balance the movement of growth upwards is compensated by an equal movement of the plant downwards, with the result that the record remains horizontal. The effect of an external agent is immediately detected by the upsetting of the balance, up-record representing acceleration above normal, a down-record the opposite effect of depression below the normal rate. The latent period and the after-effect of stimulus may thus be obtained with the highest accuracy. The sensitiveness of the Method of Balance may be raised so as to indicate a variation of rate of growth smaller than 1⁄1000 millionth of an inch per second. "Plant Response"—p. 413. XXIII.—ON TROPIC MOVEMENTS By Sir J. C. Bose. The diverse movements induced by external stimuli in different organs of plants are extremely varied and complicated. The forces in operation are manifold—the influence of changing temperature, the stimulus of contact, of electric current, of gravity, and of light visible and invisible. They act on organs which exhibit all degrees of physiological differentiation, from the radial to the dorsiventral. An identical stimulus may sometimes induce one effect, and at other times, the precisely opposite. Thus under unilateral stimulation of light of increasing intensity, a radial organ exhibits a positive, a dia-phototropic, and finally a negative response. Strong sunlight brings about para-heliotropic or 'midday sleep' movement, by which the apices of leaves or leaflets turn towards or away from the source of illumination. The teleological argument advanced, that in this position the plant is protected from excessive transpiration, does not hold good universally; for under the same reaction, the leaflets of Cassia montana assume positions by which the plant risks fatal loss of water. In Averrhoa carambola the movement is downwards, whichever side is illuminated with strong light; in Mimosa leaflet the movement, under similar circumstances is precisely in the opposite direction. The photonastic movement, apparently independent of the directive action of light, has come to be regarded as a phenomenon unrelated to phototropic reaction, and due to a different kind of irritability, and a different mode of response. So very anomalous are these various effects that Pfeffer, after showing the inadequacy of different theories that have been advanced, came to the conclusion that "the precise character of the stimulatory action of light has yet to be determined. When we say that an organ curves towards a source of illumination because of its heliotropic irritability, we are simply expressing an ascertained fact in a conveniently abbreviated form, without explaining why such curvature is possible or how it is produced."[2] The contradictory nature of the various responses is however not real; the apparent anomaly had lain in the fact that two definite fundamental reactions of opposite signs induced by stimulus had not hitherto been recognised and distinguished from each other. The innumerable variations in the [Pg 266] [Pg 267] [1] [Pg 268] [Pg 269] resultant response are due to the summation of the effects of two fluctuating factors, with further complications arising from: (1) difference in the point of application of stimulus, (2) the differential excitability of the different sides of the responding organ, and (3) the effect of temperature in modifying tropic curvature. It is therefore most important to have the means for automatic record of continuous change in the response brought about by various factors, which act sometimes in accord, and at other times in conflict. The autograph of the plant itself, giving a history of the change in response and its time-relations, is alone decisive in explanation of various difficulties in connection with plant movements, as against the various tentative theories that have been put forward. The analysis of the resulting effect, thus rendered possible, casts new light on the phenomena of response, proving that the anomalies which had so long perplexed us, are more apparent than real. One of the causes of uncertainty lay with the question, whether response changed with the mode of stimulation. I have, however, been able to show that all forms of stimuli induce a definite excitatory reaction of contraction (p. 218). Tropic movements induced by unilateral action of stimulus may, broadly speaking, be divided into two classes depending on the point of application of stimulus: In the first, the point of application of unilateral stimulus is not on the responding organ itself, but at some distance from it. The question therefore relates to Longitudinal Transmission of effect of stimulus. In the second, unilateral stimulus acts directly on the responding organ. For the determination of the resultant movement, it is necessary to take account of effects induced on the two sides of the organ. The side adjacent to the stimulus I shall designate as the proximal, and the diametrically opposite as the distal side. The question to be investigated in this case relates to Transverse Transmission of effect of stimulus. It will be shown that the resulting movement depends on:— (a) whether the tissue is a conductor or a non-conductor of excitation in a transverse direction, and (b) whether it is the proximal, or the distal side of the organ that is the more excitable. In connection with the response to environmental changes, a source of uncertainty is traceable to the absence of sufficient knowledge of the physiological effect of heat, which has been regarded as a form of stimulus: it will be shown that heat induces two distinct effects dependent on conduction and radiation. We shall in the succeeding chapters, take up the study of the physiological effects induced by changes in the environment. Pfeffer—Ibid—Vol. II, p. 74. XXIV.—TROPIC CURVATURE WITH LONGITUDINAL TRANSMISSION OF EFFECT OF STIMULUS By Sir J. C. Bose, Assisted by Guruprasanna Das. I have in previous chapters explained that the direct application of stimulus gives rise in different organs to contraction, diminution of turgor, fall of motile leaf, electro-motive change of galvanometric negativity, and retardation of the rate of growth. I have also shown that indirect stimulation (i.e. application of stimulus at some distance from the responding organ) gives rise to a positive or erectile response of the responding leaf or leaflet (indicative of an increase of turgor), often followed by normal negative response. The positive impulse travels quickly. The interval of time that elapses, between the application of stimulus and the erectile response of the responding leaf, depends on the distance of the point of appli...