Sir J. C. Bose.
The autonomous activity of growth is ultimately derived from energy supplied by the environment. The internal activity may fall below par with consequent diminution or even arrest of growth; this condition of the tissue I have designated as sub-tonic. The inert plant can only be stirred up to a state of activity by stimulus from outside; and we saw that under the action of stimulus the rate of growth of a sub-tonic tissue was enhanced.
As the general question of depression of autonomous activity and its restoration by the action of stimulus is of much theoretical importance, I shall describe experiments carried out on a different form of autonomous activity, seen in spontaneous pulsation of the lateral leaflets of Desmodium gyrans. Under favourable conditions of light and warmth these leaflets execute vigorous movements, the period of a single pulse varying from one to two minutes. As the energy for this activity is ultimately derived from the environment, it is clear that isolation from the action of favourable environment will bring about a gradual depletion of energy with concomitant decline and ultimate cessation of spontaneous movement. For this we may keep the plant in semi-darkness; we may further hasten the rundown process by isolating the leaflet from the parent plant. A leaflet immersed in water was kept in a dimly lighted room; it was attached by a cocoon thread to the recording lever of an Oscillating Recorder to be fully described in the next Paper. The pulsation continued even in this isolated condition for about 48 hours, after which the spontaneous movement came to a stop. Further experiments showed that the arrest of pulsation was not indicative of mortality but of ‘latent life’ in a state of suspense, to be stirred up again by shock stimulus into throbbing activity.
REVIVAL OF AUTONOMOUS PULSATION UNDER STIMULUS.
Experiment 90.—In figure 84, is a seen record of the action of light on the sub-tonic Desmodium leaflet at standstill. A narrow pencil of light from electric arc was first thrown on the lamina in which the presence of chlorophyll rendered photo-synthetic action possible. This had no effect on the renewal of pulsation. But the autonomous activity was revived by the action of light on the pulvinule. This preferential effect on pulvinule showed that the renewal of activity was due not to photo-synthesis but to the stimulating action of light. The pulsation was also restored by chemical stimulants, such as dilute ether, and solution of ammonium carbonate.
Fig. 84.—Renewal of autonomous activity in Desmodium gyrans at standstill by action of light. Up-curve represents up-movement. The horizontal lines below represent durations of exposure to light.
As regards the action of light, the pulsation continued for a time, even on the cessation of light. This persistence of autonomous activity increases with the intensity and duration of incident stimulus, that is to say with the amount of incident energy. In the present case a duration of five minutes’ exposure gave rise to a single pulsation, after which the movement of the leaflet came to a stop. The next application lasted for ten minutes and this gave rise to four pulsations, two during application, and two after cessation of light. The next application was for forty-five minutes, and the pulsation persisted for nearly an hour after the cessation of light. The experiments on sub-tonic specimens show clearly that the energy supplied by the environment becomes as it were latent in the plant, increasing its potentiality for work.