THE DEATH- SPASM IN PLANTS 1 55 



why older leaves give less motile indication than the young, 

 in response to stimulus in general. 



(b') By observation of spasmodic movement of uncurling. — 

 I shall now proceed to demonstrate that the death- move- 

 ment which we have seen in Mimosa is in its essentials 

 characteristic of anisotropic response in general ; and this 

 may be shown by taking a spiral tendril of Passiflora which 

 has become anisotropic by curling. In order to detect and 

 measure with ease the responsive movements of uncurling 

 and curling the experiment is arranged as follows : a light 

 index is attached to the tip of the spiral, and the whole is 

 immersed co-axially in a glass cylinder filled with water. A 

 strip of paper, marked with degrees, is wrapped round the 

 outside of the cylinder on the plane of the index. The 

 temperature of the water is now raised very gradually, and 

 the responsive excursion of the index is read on the graduated 

 circle formed by the paper. 



It is to be borne in mind that the true excitatory response 

 of the tendril is given by uncurling, which here corresponds 

 to the fall of the leaf of Mimosa ; thus the movement of 

 erection would be represented by that of curling. In the 

 case of Mimosa we saw that the first effect during rise of 

 temperature (due to absorption of water and relaxation) was 

 slow and gradual erection. On the arrival of the death- 

 point of the organ, however, this preliminary rise was 

 succeeded by a sudden responsive fall. The subsequent re- 

 laxation of death then produced an opposite movement, of 

 erection. Similarly, in the death-response of the spiral 

 tendril of Passiflora, we observe parallel phases. There was 

 first a slow and continuous movement of curling, during the 

 preliminary stages of warming. But this movement ceased 

 when a temperature of 57 C. was reached, and the tendril 

 remained stationary for a time. At 59 C, however, there 

 was produced a sudden excitatory response of death by an 

 uncurling, executed with great rapidity, an angular movement 

 of 360 degrees being described by the index during the course 

 of the next few degrees of rise in temperature. With regard 



