154 



PRACTICAL BOTANY 



the larkspur, and many other plants, open at or near the top, 

 and for weeks allow the seeds to be scattered by the wind when- 

 ever the stalks of the cap- 

 sules are swayed back and 

 forth by it. Such stalks are 

 still more strongly swayed 

 by a passing animal, and 



FIG. 146. Burs of sticktights (Desmodium) 

 One half natural size 



then throw many seeds directly 

 at the animal, into whose fur 

 they fall and are carried till 

 they shake out. 



Some fruits or clusters of 

 them, as white pine cones, or 

 whole plants, known as tum- 

 bleweeds (Fig. 356), are rolled 



along the ground by the wind, carrying with them multitudes of 

 seeds. Among the commonest are old witch grass (Panicum), 

 tumbleweed {Amaranihus), and the " Russian thistle " (Salsola). 



FIG. 147. Head of fruits of avens 



and some of the separate, bur-like 



fruits, with hook-like remains of 



the style 



The latter one and one-half times 

 natural size 



