STIMULATION AND ITS RESULI'S 375 
That these movements are essentially dependent on 
the power of the protoplasm to receive impressions from 
without, or in other words upon its possession of tone, can 
be seen from a study of the conditions under which they 
are performed. When the soil is too dry, or when from 
any other cause the protoplasm in the cells is not supplied 
Fic. 155.—Punvinus or Mimosa, 
u, 6, the succulent parenchyma of its upper and lower sides; c, bud; 
d, parenchyma of Rachis; e, pith. 
with water in sufficient quantity, they cease. When the 
temperature is too low they are interfered with. Violent 
disturbance of the protoplasm by shaking the plant will 
in some cases prevent their occurrence for one or two 
nights. : 
The purpose of the movement is somewhat obscure ; it 
