228 Prof. Bose and Mr. Das. Physiological Investigations with 



taken that the pulvinus was shaded all the time. The alternate action of 

 light and darkness on leaflets induced no variation in the uniformity of 



response. This shows that the observed 

 variation of excitability in Mimosa under 

 the alternate action of light and darkness 

 is not attributable to the photosynthetic 

 processes. 



I next took a petiole-pulvinus prepara- 

 tion from which the sub-petioles bearing 

 the leaflets had been cut off, and placed it 

 in a room illuminated by diffused daylight. 

 The normal responses were taken, the 

 temperature of the room being 30° C. 

 The room was darkened by pulling down 

 the blinds, and records were continued in 

 darkness. The temperature of the room 

 remained, unchanged at 30° C. It will be 

 seen from records given in fig. 12 that in 

 darkness there is a great depression of 

 excitability. Blinds were next pulled up, 

 and the records now obtained exhibit the normal excitability under light. 

 The sky had by this time become brighter, and this accounts for the slight 

 enhancement of excitability. This experiment proves conclusively that light 

 has a direct stimulating action on the pulvinus, independent of photo- 

 synthesis. 



Fig. 12. — Stimulating action of light, 

 and depressing action of darkness. 



11. Effect of Desiccation and of Injury on Conducting Tissues. 



I have, in my paper on " Transmission of Excitation in Mimosa,"* already 

 referred to, shown that transmission of excitation in the plant is a process 

 fundamentally similar to that taking place in the animal nerve ; it has also 

 been shown that the effects of various physical and chemical agents are the 

 same in the conducting tissues of the plant and of the animal. 



Effect of Application of Glycerin. — It is known that desiccation, generally 

 speaking, enhances the excitability of the animal nerve. As glycerin, by 

 absorption of water, causes partial desiccation, I tried its effect on conduction 

 of excitation in the petiole of Mimosa. Enhancement of conducting power 

 may be exhibited in two ways : first, by an increase of velocity of trans- 

 mission ; and, secondly, by an enhancement of the intensity of the 



* ' Phil. Trans.,' B, vol. 204 (1913). 



