Physiologists, in order to know the heart of man, play with those of the frog and tortoise. "To know the heart," be it understood, is here meant in a purely physical, and not in a poetic sense. For this it is not always convenient to employ the whole of the frog. The heart is therefore cut out, and make the subject of experiments, as to what conditions accelerate, and what retard, the rate and amplitude of its beat. When thus isolated, the heart tends of itself to come to a standstill, but if, by means of fine tubing, it be then subjected to interval blood pressure, its beating will be resumed, and will continue uninterrupted for a long time. By the influence of warmth, the frequency of the pulsation may be increased, but its amplitude diminished. Exactly the reverse is the effect of cold. The natural rhythm and the amplitude of the pulse undergo appropriate changes, again, under the action of different drugs. Under either, the heart may come to a standstill, but on blowing this off the beat is renewed. The action of chloroform is more dangerous, any excess in the dose inducing permanent arrest. Besides these, there are poisons also which arrest the heart beat, and a very noticeable fact in this connection is, that some stop in a contracted, and others in a relaxed condition. Knowing these opposed effects, it is sometimes possible to counteract the effect of one poison by administering another.
I have thus briefly stated some of the most important phenomena in connection with spontaneous movements in animal tissues. Is it possible that in plants also any parallel phenomena might be observed? In answer to this question, I may say that I have found numerous instances of automatic movements in plants.
RHYTHMIC PULSATIONS IN DESMODIUM
The existence of such spontaneous movements can easily be demonstrated, by means of our Indian Bon charal, the telegraph plant, or Desmodium gyrans, whose small leaflets dance continually. The popular belief that they dance in response to the clapping of the hands is quite untrue. From readings of the scripts made by this plant, I am in a position to state that the automatic movements of both plants and animals are guided by laws which are identical.
Firstly, when, for convenience of experiment, we cut off the leaflet, its spontaneous movements, like those of the heart, come to a stop. But if we now subject the isolated leaflet, by means of a fine tube, to an added internal pressure of the plant's sap, its pulsations are renewed, and continue uninterrupted for a very long time. It is found again that the pulsation frequency is increased under the action warmth, and lessened under cold, increased frequency being attended by diminution of amplitude and vice versa. Under either, there is temporary arrest, revival being possible when the vapour is blown off. More fatal is the effect of chloroform. The most extraordinary parallelism, however, lies in the fact that those poisons which arrest the beat of the heart in a particular way, arrest the plant—pulsation also in a corresponding manner. I have thus been able to revive a leaflet poisoned by the application of one, with a dose of a counteracting poison.
Let us now enquire into the causes of these automatic movements so-called. In experimenting with certain types of plant-tissues, I find that an external stimulus may not always evoke an immediate reply. What happens, then, to the incident energy? It is not really lost, for these particular plant-tissues have the power of shortage. In this way, energy derived in various ways from without—as light, warmth, food, and so on—is constantly being accumulated, when a certain point is reached, there is an overflow, and we call this overflow spontaneous movement. Thus what we call automatic is really an overflow of what has previously been stored up. When this accumulated energy is exhausted, then there is also an end of spontaneous movements. By abstracting its stored-up heat—through the application of cold water—we can bring to a stop the automatic pulsations of Desmodium. But on allowing a first accession of heat from outside, these pulsations are gradually restored.
In the matter of these so-called spontaneous activities of the plant, I find that there are two distinct types. In one, the overflow is initiated with very little storage, but here the unusual display of activity soon comes to a stop. To maintain such specimens in the rhythmic condition, constant stimulation from outside is necessary. Plants of this type are extremely dependent on outside influences, and when such sources of stimulus are removed, they speedily come to an inglorious stop. Kamranga or Averrhoa is an example of this kind. In the second type of automatic plant activity I find that long continued storage is required, before an overflow can begin. But in this case, the spontaneous outburst is persistent and of long duration, even when the plant is deprived of any immediately exciting cause. These, therefore, are not so obviously dependent as the others on the sunshine of the world. Our telegraph-plant, Desmodium or Bon charal, is an example of this.
It appears to me that we have here a suggestive parallel to certain phenomena with which this audience will surely prove more familiar than I, namely, the facts of literary inspiration. For the attainment of this exalted condition, also, is it not necessary to have previous storage, with a consequent bubbling overflow? Certain indications incline me to suspect that perhaps in this also we have an example of so-called spontaneity, or automatic responsiveness. If this be so, aspirants, to the condition might well be asked to decide in whose footsteps they will choose to tread—those of Kamranga, with its dependence on outside influences, and inevitably ephemeral activity, or those of Bon charal, with its characteristic of patient long enduring accumulation of forces, to find uninterrupted and sustained expression.
THE PLANT'S RESPONSE TO THE SHOCK OF DEATH
A time comes when, after one answer to a supreme shock, there is a sudden end of the plant's power to give any response. This supreme shock is the shock of death. Even in this crisis, there is no immediate change in the placid appearance of the plant. Drooping and withering are events that occur long after death itself. How does the plant then, give this last answer? In man, at the critical moment, a spasm passes through the whole body, and similarly in the plant, I find that a great contractile spasm takes place. This is accompanied by an electrical spasm also. In the script of the Morograph, or Death recorder, the line that up to this point was being drawn, becomes suddenly reversed, and then ends. This is the last answer of the plant.