204 MIMOSA. [CH. VIII 



one of Sachs' experiments 1 a plant was placed in the dark 

 at 9 p.m. Sept. 24, and on Sept. 27 at 9 a.m. sensitiveness 

 had almost, and on 28th, quite disappeared. It was 

 then exposed to light and took some days to recover. 



(235) Mimosa : continued stimulation. 



A light stick about 25 cm. in length is transfixed by a 

 needle at about 6 cm. from one end ; the ends of the 

 needle are pushed into rubber corks, which are held in a 

 clamp. Since the needle cannot turn easily in the 

 rubber which supports its two ends, the stick will stand 

 out horizontally : a slight blow on the short end of the 

 lever makes the other end jump up, and the elasticity of 

 the corks brings it back to its old position ; if repeated 

 blows are thus applied, the long arm will make corre- 

 sponding beats upwards. These can be applied to the 

 leaf of the Mimosa by a pin fixed at the end of the 

 lever so as to strike the pulvinus across its longitudinal 

 axis. The rhythmical blows are applied to the short end 

 of the lever by drops of water falling from a height of 

 30 cm. at the rate of 8 or 10 per minute. 



With this arrangement the leaf falls at first, but 

 as the blows are continued the petiole rises, and after 15 

 minutes is insensible not only to the light blow of the 

 lever (otherwise it would not have risen) but also to a 

 more severe disturbance. 



The above method is a slight modification of Pfeffer's 2 . 

 Another plan is to tie a thread to a branch of the plant, 



1 Physiologie (French Trails.), p. 49. 



2 Pltysiol. Untersuclmnyen, 1873, p. 57. 



