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 
Fic. 159.—Lear or Dionea muscipula, 
1, open; 2, closed: a, lateral view, 6, surface view; 3. one of the sensitive spines 
( x 60); 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 Dionwa (fig. 159) is due algo 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 
