Growth and Movement. 



129 



may approximate or even surpass in some respects that of 

 animals. 



100. Spontaneous Movements. — The movements of plants 

 which have thus far been mentioned are evidently induced 



Fig. 66. 



Two photographs of the same seedling Morning Glory. A, after growing under 

 usual conditions, the light stronger from the right ; B, after revolving on a uni- 

 versal axis immediately following the condition shown in A. 



or guided by some external force, although in all cases the 

 protoplast is the immediate cause of the movement. There 

 is, however, another class of movements which seem to 

 require no external stimulus other than those conditions 

 which are necessary to the healthy existence of the plant. 



