276 CHAP. XXV. DIURNAL MOVEMENT OF MIMOSA 



2 P.M., as shown in the horizontal character of the curve. 

 On restoration of Hght (at the point marked with the second 

 thick dot) the leaf moved upwards till the positive photo- 

 tropic movement attained a maximum in the course of 

 I hour and 20 minutes, after which neutralisation set in, and 



Fig. 160. EfEect of periodic alternation of darkness d, light l, 

 and~of darkness d, on the response of Mimosa leaf. The 

 first' darkness causes the pre-maximum after-effect of slight 

 erection followed by recovery. The subsequent exposure 

 to light from 2 to 4 p.m. caused erectile movement followed 

 by partial neutralisation by 4 p.m. Stoppage of light at 

 the third thick dot caused a sudden fall of leaf below the 

 position of equilibrium. 



by 4 P.M. the positive phototropic effect had become 

 partially neutralised. Artificial darkness at the third 

 thick dot caused a rapid down-movement which overshot 

 the position of equilibrium. The difference of after-effect 

 in the forenoon and in the afternoon lies in the fact that 

 in the first case it was a pre-maximum after-effect, whilst in 

 the second case it was a post-maximum after-effect. 



The record of the responses of Mimosa just described 

 was obtained in the course of experiments which lasted 



