The Motor Mechanism of Plants

automatic movement. Under favourable conditions for the absorption of energy from without, an ordinarily responding plcint becomes converted into an automatically moving plain like Desmodium. Conversely, under unfavourable circumstances involving isolation from the stimuli of its normal environment, the leaflets of an automatically responding plant like Desmodium come to a state of standstill , it then oecomes converted into an ordinarily responding plant like Biophytum (p. 245). Automatic or spontaneous pulsation is therefore not self-originated, but is really due to the previous absorption of energy from the stimuli of the environment.

the tonic condition is the expression of this energy- content of any tissue, and it is this that determines its physiological fitness for the normal performance of its proper function. The question naturally arises whether the energy derived from incident stimulation contributes in any degree to the performance of its normal function hy the stimulated tissue. There are certain facts which can be most satisfactorily explained on the assumption that the energy derived from stimulation can be so utilised. Instances of this are seen in the revival of pulsation of Desmodium under electric and photic stimulation (p. 236) ; in the revival of the pulsation of the heart under electric stimulation (p. 259) ; in the renewal of the peristaltic activity of- the stomach by electric, mechanical, chemical, and thermal stimulation (pp. 283-285) ; and in the revival or enhancement of pul¬ satory activity in the propulsive tissue of the sap by photic stimulation (pp. 302, 334).

The essential identity of the rhythmic mechanism in the plant and animal is proved by the following evidence that pulsation in the plant is a fleeted by the same agents and in the same way as pulsation in the animal. animals, such as the beating of the heart and the move¬ ments of the alimentary canal. These movements are what is termed ' peristaltic,’ consisting of waves of contraction travelling along the organ iri the direction of propulsion. Is there anything of this kind to be found in plants ?

Years ago, I published a work (‘ Physiology of the Ascent of Sap/ 1922) in which 1 demonstrated .that the sap is dis¬ tributed in the plant-body by the activity of certain of its living cells, which pulsate automatically after the manner of the animal heart. These cells, which exist in all parts of the body, were located in the stem by the Electric Probe, as belonging to the inner cortex (p. 329). Further investiga¬ tion has thrown light upon the nature of this movement, making it clear that the movement of the sap is effected by rhythmic contraction and expansion of the cells of the propulsive tissue, constituting, as in the heart and stomach of tiie animal, waves of peristaltic activity.

The Law of the Propagation of Peristaltic Waves was established by experiments carried out with the animal stomach. It was shown that the peristaltic wave follows the stimulation-gradient from the stimulated to the unstimulated region (p. 292). It has also been Sxiown that the direction of movement of the sap can- be determined by differential stimulation of the two ends of the organ, its flow being always from the more to the less stimulated region, whether upwards or downwards (pp. 318, 346, 357).

The results obtained with the sealed stem with its activity at standstill, an exactly parallel to those obtained with the quiescent stomach. In both, a peristaltic or an antiperistaltic wave is generated by stimulation, the direc¬ tion of propagation following the stimulation -gradient from the more to the less activated region (p. 402). In both, the peristaltic wave is about four times more rapid than the antiperistaltx (pp. 289, 346). An identical Pw is thus illustrated by the passage of the peristaltic wave in both the animal and the plant.

ibe object of the experiments with sealed stenib was to ascertain whether or not sap-movement could be induced in the stem without the co-operation, of leaf or root and without loss or gain of water. It was so induced, conse¬ quently the results prove the existence in the plant of an independent propulsive mechanism, which works in the same peristaltic way as the heart and the stomach of the animal. I now give a brief summary of the results upon which the assertion of the identical nature of the pulsatory mechanism in the plant and in the animal is based.

It has been shown that pulsation in the plant, whether external or internal, is affected by the same agents and in the same way as pulsation in the animal. Effect of variation of internal pressure . — A diminution of internal hydrostatic pressure under drought causes arrest of the pulsation of the Desmodium leaflet, which becomes revived under increased hydrostatic pressure after irrigation (p. 256). The pulsation of the propmsive tissue in the stem is depressed under drought and enhanced after irrigation (p. 332). In the quiescent heart the pulsation is revived by an increase of intra-cardiac pressure vp. 256). The arrested pulsation of the stomach is also revived by internal distension (p. 290).

Effect of variation of tempera lurc. — The fact that all pulsatory activities are depressed by a fall 0+' temperature and increased by a rise, has been demonstrated by the parallel changes induced, in the pulsation of the Desmodium leaflet (p. 264). in the pulsation of the heart (p. 266) and of the stomach (p. 282), and in the rate of ascent of Sap Necessity of oxygen for the maintenance of pulsation. — The pulsation of the Desmodium leaflet is arrested by

deprivation of oxygen, and specially by the asphyxiating action of CC2 ; the arrested pulsation is revived by fresh supply of oxygen (p. 257)* Similar effects are observed in the case of the pulsation of the heart (p. 258) and in that ol the stomach (p. 280}'. The effects of drugs are, however, the most significant evidence in proof of the identity of the physiological mechanism in the animal and in the plant. Stimulants, like dilute solution of Camphor, which enhance the activity of the animal heart (p. 373) also induce an enhanced activity of the propulsive tissue in the plant, exhibited by a sudden increase of sap-pressure in \vhich the individual pulsation shows an up-stroke larger than the down-stroke (p. 374).

Morphine causes a depression oFthe heart-beat (p. 578) ; its action on the pulsation of the plant is a diminution of pressure, the down-stroke of each individual pulsation being larger than the up-stroke (p. 375). The same antagonk tic action of different drugs is exhibited in both plant and animal. Muscarin and Pilocarpin cause arrest of the heart, whereas A tropin, by its physiological antagonism, revives the activity. Effects exactly parallel are induced in the pulsating leaflet of Desmodium (p. 270).

The characteristic edects of various drugs on plant and animal are so very similar that the physiological action of extracts of various plants on the act.iT,ity of the animal heart has been discovered by their action on he pulsating tissue of the plant (p. 270). These results offer further convincing p^'oof that the mechanism for the propulsion of the sap in the plant is physiologically similar to that for the circulation of the blood in the animal.

lo sum up all the accumulated experimental evidence adduced in the pages of this book, it has first of all been demonstrated that the familiar and striking movements of * sensitive ’ plants are accompanied by all the physiological signs — such as electromotive variation, behaviour under change of external conditions end under the action of anaesthetics and other drugs reaction to stimulation — which are characteristic of the contraction animal muscle. It must the re lore be concluded that the motile organs of these plants include a tissue which closely .esembles animal muscle in its properties.

It Las also been shown tnat ordinary, non-sensitive, plants respond to stimulation by movement which is not always perceptible, but can be detected by sensitive apparatus with high magnification. I heir response has been shown to be accompaniea by all the physiological signs which are characteristic of that of sensitive plants. Moto- excitability ;s therefore not limited to certain olants, but is possessed by them all. It has been further demonstrated that just as in the animal body there is a rhythmic pe istaltic movement of internal organs concerned with the circulation of the blood and with the propulsion of food along the alimentary canal, so also in the plant-body there is a similar peristaltic move¬ ment in a tissue distiibuted throughout it, which constitutes the organ for the propulsion of die sap. All the experi¬ mental conditions which affect the movement of the heart 01 the stomach of the animal have been proved to affect in just the same way the activity of the dssue effecting the propulsion of the sap in the plant. Here again similarity, of behaviour justifies the assertion of physiological identity. Nor is this identity surprising; for there is a common factor in the motor mechanism of plant and animal, the moto-exritability of the protoplasm of which they both consist. « ; w * • p «

The gradual evolution of the motor mechanism has been traced, through intermediate types, from the simplest to the most complex. The study of the life of the plant thus assumes its true importance and significance, not only from the evolutionary point of view, but also from the prospect it holds out of pointing the way to the solution of many or the p erplexing problems in the life of the animal. 1 ne life-movements of plants must therefore be regarded as an integral part of the study of the general physiology of living organisms, without which that study will be but partial and incomplete.

Accession and depletion of energy under stimulation, 48, 54, 234, 407 Acid and alk; li, antagonistic action of, on mechanical response, 87-8, 408 Active and inactive pulvinus and muscle, 64, 65 Age. effect of, on moto-excitability, 81, S3 ; on response to photic stimula¬ tion, 178 Ammonia, effect of, on moto-excitability, 76 ; on rhythmic movement, 2 73, ile of transpiration 343; rate of, in intact and in isolated stem, 353 * normal ascent due to differential stimulatio; See also under Sap m- vefnenfe ' *

Automatic recorder, for diurnal variat’ m of excitabditv, 91, 92 Automaticity, different grades of, in sinus, auricle an 1 ventricle of heart, Averrhoa, polar action of ciurent on, 108, no; transmission of death- excitation in, 214 Barium chlorine, effect of, on contractile response, 87, 408 Basella, death-spasm of stem of, 208 ; death-record by variation of eight, 223 Biophytum sensitivum 75 ; single mechanical response of, 25, 238 , multiple mechanical response under strong stimulation, 238, 239; 41 1 ; multiple electric response of, 239; multiple response under direct photic stimulation, 240; polar action of current on, 109; transmission of death-excitation in, 216 Block, method of, in torsional stimulation, 169

Bubble-method for investigating the directive movement of sap, 355 Carbon disulphide, effect of, on contractile resp mse, 76 Cardiac activity, study of induced variation of, 251-2 : myog nic and neurogenic theories of, 252; characteristic features of, 2 54* 414; erfect of thermal stimulation on, 265 ; effect of drugs on, 267* 415 Cardiogram, characteristics of, in different animals, 249-251 Cardiograph, Resonant, 2 48 Carissa Carandas, death-record of, by apparent variation in weight, 221,

Cellular contraction and expansion under drought and irrigatjpn, 15U, 1 Cellular contraction under stimulation, 134 et seq., 160, 16 1 measurement of, in Mimosa pulvinus, IJ29 et se \ •* Cellular mechanism : continuity of, in the plant, 142, 162 ; for propulsion Conduction of excitation, 13 ; in flower stalk of Biophytum, 216 Conductivity, independent of moto-excitability, 80, 81 Contractile cells; continuity of, between stem and leaf, 140, 141 317, 324 granular character of protoplasm in active, 64, 67 ,, response, similarity of, in plant and animal, 68, 406 ,, tissue, demarcation of, in pulvinus, by differential staining, 61 et seq., 407

Desmodium gyrans, 229 ; record or pulsation of, 229 et seq. ; automatic pulsation of, 247 Desmodium pulsation, dependence of, on storage of energy, 234, 246; effect of electric stimulus on arrested pulsation, 236, 240; effect of light on, 236; record of pulsation of isolated pulvinus, 253 ; effect of drought and irrigation on, 255, 256, 414 ; asphyxiating action of carbon dioxide on, 257, 2S0 ; effect of oxygen on, 256, 257, 280; effect of variation of temperature on, 262 et seq., 414 ; critical tem¬ perature for arrest of, 263 ; effect of spirit, amnion, aromatic, on, 267, 268 ; effect of extract of Abroma augusia on, 271, 272 ; effect of small and large dose of potassium bromide on, 268 ; antagonistic action of Pilocarpin and Atropin on, 270

Diametric contraction, method of, 130 et seq. S&'e under Cellular contrac¬ tion Differential excitability, determination of, in pu Ivinas of Mimosa, 148; m leaf-joint, J40 ; in petiole, 149 Differential stimulation, effect of, on direction of peristaltic wave in stomach, 292 ; on direction of propulsion of sap in plan-', 337 ,, stimulation, effect of, on Desmodium pulsation, 23' , 260 et seq. ; on pulsation of heart, 239 ; on pulsation cr stomach, 283 ; on propulsion of sap, 302

Erythrina indica : mechanical response of, 26 ; effect of stains on pulvinus of, 63, 64 Ether, effect of, on moto-excitability of Mimosa, 73, 408 Eucharis Lily, sensitiveness to cold, 175 Excitability, determination of scale of, by differential staining, 63, 67 ; effect of age on, 83 ; rate of decay of, after section, 83-5 ; effect of external variations on, 93 et seq., 9S ; diurnal variation of, 90, 96-9, 102, 105 ; seasonal variation of, 102 Excitatory reactions of different plant-organs, 205 Expu’sion of sap from stimulated cells, 8

Fatigue-reversal under continuous stimulation, 47 Flowers, death-movement of, 207 Geotropism, induction of anisotropy by, 153, 406 Glycerine, effect of, on water-logged tissue, 71 Gourds, death-record of stem of, 224 Haberlandt, on light-perception of plants, 10 ; on expansive reaction of upper half of Mimosa pulvinus, 28 Hsematoxylin and Bismarck Brovn, staining reaction with, 62 Heart, automatic pulsation of, 229, 243; effect jf external agents on. 414; peristaltic wave in, 275, 286; rhythmic mechanism of, 248. See also under C rrdiac activity

Helianthus (Sunflower), response of, by variation of resistance, 191-3 ; residual current in bare stem, 3.49 ; responsive variation under differenti 1 stimulation, 350 et seq. ; rate of ascent of sap in, 354 liering, assimilation and dissimilation, 54 Hibiscus, death-response at fatal temperature, 197 ; movement of sap in, Indian plants, physiological action of extracts from, 270-2, 273 415 Induction-shock, calibration of intensity of, 12-13 1 stimulation by, 1 1 Inertia, physiological, effect of, On response, 101 Interaction and intercommunication in plant, 401, 4c 2 Iodine-Green and Alum-Carmine, staining reaction with, 62 1‘pomoea pulchella, response of, by variation of electric res’v iance, 191

Leaf-joint, anisotropy and differential excitability in. 149 Leaf-movement, action of poison on, 297 ; its relation to the propulsion of sap, 298 Mercuric chloride, action on plant, 216 Methylene Blue and Erythrosin, staining reactions with, 61 Mimosa fiudica, 6, 78 ; mechanical response of, 24 ; contractility of upper half of pulv mis, 28 ; unequal pliability of pulvmus, 30 ; re¬ sponse of, in inserted position, 33, 407 ; effect of weight of leaf on response, 34 ; comparison of excitability of two halves of pulvinus, 37 ; characteristic difference of response of highly excitable and sub- tonic pulvinus, 39 ; dependence of amplitude of response on number of excited cells, 40, 40S ; rate of mechanical recovery dependent upon ascent of sap, 41 ; rate of work performed by failing leaf, 41 ; latent period of response of, 44 ; additive effect of stimulation on response, 45; uniform responses of, 46; fatigue-relaxation of, 47; erectile response of subtonic specimens, 50, 410 ; transformation of response from posithe to negative, 50; rapidity of contraction, dependence of, on presence of active rnbstance, 60, 138, 407; demarcation of active and inactive pulvinar cells by staining, 61, 407 ; effect on moto-excitability, of variati m of light, 69, 36 ; of excessive turgor, 70-2, 94, 168 ; of variation of turgor, 99 ; of change of temperature, 72, 94, 95, 96; of ozone, 737 of carbon dioxide, 73, 122; of sul¬ phuretted hydrogen, 74; ot ether, 75; of chloroform, 76, 122; oi barium ch'oriae, 87 ; of acid and alkali, 87, 88 ; of campuor, 123 ; of caffein, 1^5; of musk, 1-5; of strychnine, 126; inhibition of response by excessive absorption of water, 70, 168 ; diurnal variation of excitability of, 90, 407 ; petiole-pul vinus prep.i ration of, 78-80, 85, 88, 406 ; isolated pulvinar preparation of, 118 ; electro-motive re¬ sponse of fixed Loaf, 167 ; diametric contraction in pulvinus and cortex, 137, 404 f ; death-spasm of, by scalding, 201 , by poison, 215 Mimosa Spegazzinii, excitability of, 2 Morphine, depressant action off

374, 373, 378, 379, 415 Musk, effect of, 379 ; on pulvinar response of Mimosa, T25 ; effect of, on pulsation of heart, 375, 376; on propulsive pulsation in plant, 374, Myogenic and neurogenic theories of origin of activity of heart-beat, 232 Neptunia. mechanical response of, 25; polar action of current on, no; staining reaction of pulvinus of, 64, 407 Neurogenic and myogenic theories of orig’11 of activity of heart-beat, 2.52 Nitrogen dioxide, action of, on moto-excitability, 76

Ordinary plants, diametric contraction or stem ;of, 145, 403 ; electric response of, 168 ; motor response of stem of, 142 ; polar excitation of, 1 16 ; response of leaf of, 146, 157 ; response of petiole of, J49 ; response in general, 404, 403 ; unilateral stimulation by bending of 151 Oscillating ‘Recorded, Electro-, the, 21 Oscillator, Clockwork, the, 23 Petiole, anisotropy and differential excitability of, 14 9 Petiole-pulvinus preparation of Mimosa pudich, 78 Pfeffer, on pulvinus of Mimosa, 35 Pfluger’s Law, ita

,, and sphygmogram, simultaneous, 315 Phytograph, Electro-magnetic, 18 Porana paniculate., response of, by variation or electric resistance, 191 Post-mortem relaxation, 204, 223 Potograph, deterir maiic 1 ot movement of sap by, 337-8 ; detection of directive movement under differential stimulation by, 349 et seq. Propulsive tissue, localisation of, by Electric Probe, 295, 327, 328. 335, 413 ; electric recoid of pulsation in, 330 Protoplasmic reaction, identical 'character of, under di.erse modes of stimulation, 10 ; to external stimulation, 54 Protozoa, polar action of electric current on, 106

Pulsation, automatic’, 229, 41 1 ; effect of external age rts on, in plant and animal, 414 ; cellular, electric record of, 325 ; mechanical record of, Pulvini, active, semi-active and inactive, 26, 58, 64 ; rates of contractile reaction in, 59 ; characteristic staining reactions of, 64 Pulvinule, isolated, of Desmodium pulsation of, 253, 254, 256 Pulvinus of Mimosa, anatomy of, Oo ; response of isolated, 11S Quadrant method of detecting response by variation of resistance, 194, 198, 410 ; effect, of photic stimulation, 195 ; of a single spaik, 196; of increasing intensity of light, 196

Refractory period in pulsation of Dosmodium and of animal heart, 243* 244 ,, mechanism in plant and animal, 248, Vi Rhythmicity, cause of, 244 Schwendener, on pulvinus of MimdSa,flg2 Secondary poles, 1 1 4 Semi-automatism, 245 Spiritus Ammoniae Aromaticus, effect of, on cardiac pulsation, 267; on Desmodium pulsation, 2O7, 268; on pulsation of stomach, 285, Sulphuretted hydrogen, abolition of moto-excitability by, 75 Sunflower, effect of differential stimulation on directive movement of sap