REPRODUCTION 



201 



Seed Dispersal. — It is obvious that to leave successful offspriuf;- 

 a plant must not only develop seeds but must provide for their 

 dispersal; and in bringing this about, almost as great a variety of 

 adaptive devices are employed as there are to insure cross- 

 pollination. Dependence is placed upon various agencies, but 

 chiefly the wind and animals. Many seeds or even entire fruits 

 are light and provided with wings or tufts of long hairs, so that 

 they present a large surface for the wind to catch, and are often 



Fig. 115. — Flower clusters of the 

 burdock (Arctium). The bracts which 

 surround the cluster are stout and 

 hooked, and thus aid in the dispersal of 

 the fruit. 



Fig. 



110. — Conspicuou.s berries of the 

 baneberry {Aetata) . 



wafted many miles (Fig. 114). In the case of the various 

 "tumble weeds" the entire plant breaks off at the base of the 

 stem and is rolled along over the ground by the wind. Other 

 fruits and seeds develop hooks (Fig. 115), spines, or sticky secre- 

 tions which enable them to adhere to the fur of animals or the 

 feet of birds and thus to be carried for long distances. In fleshy 

 fruits, the fleshy portion or pulp is usually bright in color (Fig. 

 116) and is rendered attractive to animals by its taste. Birds 

 are particularly important in the dissemination of the seeds of 

 such fruits. In a few cases like the witch hazel, the fruit splits 

 open with such force that the seeds are projected through the 

 air for a considerable distance. The seeds and fruits of water and 

 shore plants are usually dispersed by floating on the water and 

 have been known to travel thus for hundreds of miles. 



