THE NATURE OF FRUITS 



329 



however, of all fruits which are eaten; the seeds of some 

 are digested as well as the tissue which surrounds them. 

 Birds and grazing animals are especially helpful to plants 

 in connection with seed dispersal. They are agents by 

 which seeds are scattered widely and are deposited in 

 conditions which are favorable for their germination. 

 Edibility of the seeds themselves is, however, a disad- 

 vantage, as in the case of nuts eaten by squirrels. 



b. By their Buoyancy. Buoyancy both in the air and 

 on the water is important. The fruits of many Com- 

 posite?, buoyant in the air, and often aided in this buoyancy 

 by parachute-like structures, furnish the most familiar and 

 abundant examples of dissemination by 



wind. (See Figure 143.} All seeds and 

 fruits, even the lightest, are heavier than 

 air, so their movement through it is limited 

 and dependent chiefly upon wind. But 

 very many seeds and fruits are lighter than 

 water, and so may be carried by it for 

 great distances. The principal drawback 

 to this means of dispersal is that water- 

 soaked seeds after a time lose their vitality, 

 their power to germinate. For shore- 

 growing plants, however, water is of very 

 great importance in dispersal. 



c. By their Clinging Power. Any one who has walked 

 through woods or weed patches in late September or early 

 October can testify abundantly to the clinging power of 

 several kinds of fruits. (See Figure 144.} This, and the 

 two other properties of fruits which make for dissemina- 

 tion, are discussed further in the section on agencies of 

 seed dispersal. (Page 353.) 



FIG. 143. Fruits 

 (akenes) of dandelion. 



