ANIMAL AND VEGETABLE 



129 



mechanism of an animal is very largely either muscular or 

 glandular. /The contractile power is but little developed 

 in vegetable protoplasm, and when present it seems to be 

 rather passive than active, to produce frequently recoil 

 rather than true contraction. Still, the latter is not 

 entirely absent. . . . Though the power of contraction is 

 comparatively seldom found, it has its representative in 

 the power which vegetable protoplasm possesses of resisting 

 or assisting the transit of water. . . . The main require- 

 ment of most animals is freedom of locomotion or rapid 

 assumption by the body of new positions. The most 

 important duty of the plant is the regulation of the water 

 supply upon which its constituent protoplasts are so 

 dependent." This is chiefly, if not entirely, accomplished 

 by means of the stomata upon the under surface of the 

 leaves, which open or close in accordance with the require- 

 ments of the plant. Three of these are shown in the 

 following figure : 



Crt&zrcf Cetts 



Fig. 68. 



Surface view of part of the tinder surface oi a leaf, showing three 

 stomata in different stages of opening and closing. (After Green.) 



" The effects of stimulation may be seen in glandular 

 organs in plants as well as animals. Both Drosera and 



K 



