DISPERSAL OF SEEDS AND FRUITS 



213 



violet will throw its seeds for a considerable distance when 

 the three valves separate and bend outward. 



Distribution by Animals. Fruits and seeds that have 

 spines, hooks and sharp pointed bristle-like hairs attach 

 themselves to the fur of animals and the clothing of man. 

 By this means seeds and fruits are frequently distributed 

 many miles. 



FIG. 135. Microphotographs showing structure by means of which plants 

 adhere to objects. 1, Burgrass (Cenchrus sp.); 2, beggar-ticks (Bidens 

 frondosa); 3, common burdock (Arctium minus); 4, cocklebur (Xanthium 

 echinatuni) . 



Seeds Distributed by Birds. Most wild and smaller cul- 

 tivated fruits are distributed by birds. The distribution is 

 of course due to the fact that the seed is not destroyed while 

 passing through the bird's digestive tract. That wild plants 

 producing edible fruits are numerous is due in part to the 

 fact that birds distribute the seed. 



