ANIMALS AND PLANTS 



243 



mals which devour them, but a certain number of the 



seeds carried away are not eaten, and these are thus 



distributed more widely than would be the case were 



they to fall to the ground directly. Where the seed 



itself is not the edible part of the fruit, but is enclosed 



in an edible pulp, there is no question that we have 



to do with a case of special 



adaptation. In such cases, e.g. 



most of the ordinary cultivated 



fruits, the fleshy edible portion 



is eaten and the seeds rejected. 



Or, if the fruits are small, the 



whole fruit is eaten and the 



seeds pass uninjured through 



the body of the animal. Birds 



are especially important agents 



in the distribution of seeds, on 



account of the long distances 



over which they travel. 



Another method of distribu- 

 tion of seeds and fruits through 

 the agency of animals is seen in 

 the development of organs of 

 attachment, such as the awns of 

 grasses, the hooks and barbs de- 

 veloped by the fruits of many Compositse, Borragina- 

 cese, etc. (Fig. 54). The pedestrian who returns from a 

 ramble through the fields, covered with a varied assort- 

 ment of " burs," is but acting as Nature's unwilling 

 agent in the distribution of her plant children. Those 

 plants which we call weeds burdocks, beggar's-ticks, 

 hound's-tongue, bur-clover- -owe their success in the 



- : 



FIG. 54. A, spikelet of a grass 

 (Hordeum nutriaum^, the 

 long awn furnished with re- 

 curved barbs ; B, part of the 

 awn enlarged to show the 

 barbs; C, fruit of bur-clover 

 (Medicago) ; D, four spiny 

 fruits of the common 

 hound's-tongue (Cynoglos- 

 sum). 



