ECOLOGY OF FRUITS 



197 



What reason can be given for the fact that the burdock, 

 the cocklebur, the beggar's-ticks, the hound" s-tongue, and 

 many other common burs are among the most persistent 

 of weeds ? 



243. Uses of Stone-Fruits and Fleshy Fruits to the Plant. 

 — Besides the dry fruits, of which some of the principal 



kinds have been mentioned, 



there are many kinds of 



stone-fruits and other fleshy 



fruits (Sects. 227-230). Of 



these the great majority are 



eatable by mail or some 



of the lower animals, 



and oftentimes the 



IV 



I n 



Fig. 148. Barbb and Hooks of Burs. 



I, barbed points from fruit of beggar's-ticks (magnified eleven times) ; 

 II, hook of cocklebur (magnified eleven times) ; III, beggar's-ticlss 

 fruit (natural size) ; IV, cocklebur hook (natural size) . 



amount of sugar and other food material which they con- 

 tain is very considerable. It is a well-recognized principle 

 of botanj-, and of zoology as well, that plants and animals 

 do not make unrewarded outlays for the benefit of other 

 species. Evidently the pulp of fruits is not to be consumed 

 or used as food by the plant itself or (in general) by its 



