STIMULATION AND ITS RESULTS 



399 



and leaves of Mimosa is due to a sudden change in the 

 protoplasm of the cells on the lower sides of its pulvini, in 

 consequence of which water escapes from them into the 

 intercellular spaces between them. It is attended by a 

 change of colour, the pulvinus becoming of a deeper green 

 in consequence of the replacement of the air there by water. 

 If a leaf is cut off just above the pulvinus and the plant 



open ; 2, closed : 

 ( X 



FIG. 159. LEAF QJ? Dioncea muscipula. 



: a, lateral view, 6, surface view ; 3. one of the sensitive spines 

 50) ; 4, glands on the surface of the leaf ( X 100). 



allowed to recover from the effects of the injury, subsequent 

 stimulation of an adjacent leaf causes water to exude from 

 the cut surface of the pulvinus. The cases of the irritable 

 stamens and stigmas are probably to be explained similarly. 

 The closing of the leaf of Dioncea (fig. 159) is due also to a 

 redistribution of the water in the cells of a band of tissue 

 lying along the mid-rib, brought about by a rapid change 

 in the protoplasm, perhaps akin to contraction. In Drosera 

 the inflexion of the tentacles has been found to be preceded 



