The Sensitive Plant
The Motor Mechanism of Plants. By Sir Jagadis Chunder Bose. (Longman. 21s.) The Motor Mechanism of Plants. By Sir Jagadis Chunder Bose. (Longman. 21s.)
ANY one who has golfed in Fiji is painfully familiar with the sensitive plant, which plays so large a part in Sir Jagadis
Bose's invaluable work. The old Suva golf course was one bed
of Mimosa pudica, about as thick as clover. This is called the sensitive plant par excellence, but Sir Jagadis Bose's
careful and cunning experiments have shown that all plants are similarly sensitive in kind, though most of them are unable to make the fact evident because they are immured
in knotty trunks, like the suicides in Dante's seventh circle. The little black fore-caddies were able to trace a golf ball by the furrow caused by all the plants which it touched shutting up their leaflets in alarm. But, by the time the players arrived, they had unfolded again, and the ball would have been hope- lessly lost but for the grinning caddie standing over it. The sensitive plant is out of place on a golf course, where it necessitates niblicks and imprecations. But it has proved its value in the laboratory, and many of Sir Jagadis Bose's general conclusions originated in his experiments on Mimosa pudica.
It is, of course, no new discovery that all plants respond in some way to a stimulus from the external world. We recall the patient enthusiasm with which Darwin studied the power of movement in plants, as shown by tendrils and other parts visible to the naked eye. Vegetable growth itself—on which, in the last resort, the whole round world is at present dependent for its subsistence—consists of cellular movements due to external stimuli. To this day it is uncertain whether some of the simplest unicellular forms of life should be classified as plants or animals ; and it has long been held that there is no fundamental difference between the living substance of animals and that of plants. The novelty of Sir Jagadis Bose's work lies in his brilliant demonstration and measurement of plant movements previously unrecognized because they were too tiny to be perceived, and in his conse- quent explanation of some of the most obscure problems of vegetable physiology.
The publication of this new book practically coincides with its distinguished author's seventieth birthday. Mainly a record of selected experiments, it is in a sense a summary of the important work to which Sir Jagadis Bose has devoted his unrivalled manipulative skill during the last thirty years. The results attained by some of the ingenious instruments which are here fully described were so surprising to the elder physiologists that they were at first greeted with a certain measure of incredulity. Even as recently as 1920 there was still a controversy as to the reliability of Sir Jagadis Bose's extraordinary high-magnification instruments. An inquiry was accordingly undertaken by a committee of Fellows of the Royal Society, including Sir William Bragg, and they declared themselves satisfied that these instruments would correctly record the movements of a plant at a magnification as great as ten million times. It is not easy to realize exactly what this means. If an average man were magnified to the
same extent, he would be able to Stand comfortably with one foot in London and the other in Chicago—yery convenient for boot-legging. If the speed of an express train were similarly magnified, it could travel from the earth to the sun in about nine minutes. With the aid of the " High Magnifica- tion Sphygmograph," Sir Jagadis Bose is able to measure and exhibit the contraction of a single cell. The construction of this wonderful instrument is fully described in the present work, where we are told that a Viennese biologist has recently been able to confirm many of the author's observations with it.
Sir Jagadis Bose's interesting results are too numerous and elaborate to be here described. They will be found very clearly set forth in the brief summaries which are appended to the record of typical experiments in each chapter. To the vegetable physiologist this book cannot fail to be pro- foundly interesting and suggestive. Perhaps the most valuable of its conclusions is that which relates to the vitally important problem of the ascent of the sap in plants. This is now clearly shown to be due to an automatic pulsating or peristaltic movement, closely analogous to that of the human alimentary canal, and related to the rhythmic pulsation of the heart, on which the circulation of the blood depends. Sir Jagadis Bose claims to have traced the maintenance of this movement to a " pulsating layer " in the cortex, which is practically continuous throughout the plant. He shows that the movement of the sap is reversible ; if moisture is applied to the upper end of a cut stem the sap descends, though at a lower rate than normal, so that it is evident that the cells in the stem are doing the work. The older theories which endeavoured to explain the rise of the sap by tran. spiration, root-pressure, osmotic action, and so forth, may therefore be considered as definitely superseded.
The general reader will perhaps take more interest in some of Sir Jagadis Bose's casual and passing results, such as the discovery that a plant may actually be killed by the venom of a cobra—after which it is not difficult to believe that an oyster may be crossed in love. Very remarkable, again, is the chapter on the death-spasm in plants, corresponding to the death-throe in animals. " Blister my kidneys ! " cried Mr. Jorroeks " it is a frost ; the dahlias are dead." But that drooping of the leaves and flowers which this keen observer presumably took for a sign of death rather corresponds to the onset of putrefaction in the animal body. The actual moment of death in plants which are killed by a steady increase in temperature to a lethal degree is marked by a sudden violent contraction or electric spasm, which often takes place hours before the plant gives any of the visible signs by which its death is usually presumed to have taken place.
Sir Jagadis Bose's patient and delicate experimentation has not merely opened a new world to the physiologist : it may lead the philosopher a step further towards the conviction of the essential solidarity of life in all its manifestations, from the simplest to the most complex—towards the crowning realization of " one law, one element . . . to which the whole creation moves."
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