170 



ELEMENTARY STUDIES IN BOTANY 



ranging, from a very short distance to a very great distance, 

 as the following illustrations will show. 



FIG. 137. Seed of 

 milkweed with tuft 

 of hair. After 

 GRAY. 



FIG. 138. Seed ox nreweed with tuft of hair. 



In some plants there is a mechanical discharge of seeds 

 provided for in the structure of the seed-vessel (" fruit "). 



For example, in the 

 violet, when the 

 seed-vessel splits, 

 its walls press upon 

 the seeds so that 

 they are pinched 

 out, as a moist 

 apple-seed is pro- 

 jected by being 

 pressed between the 



FIG. 139. - Winged fruit of maple. - After KEENER. thumb and finger 



(Fig. 133). When the pod of the wild bean bursts, the 

 two " valves " twist violently and throw the seeds (Fig. 134). 



