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. 227-280). Of 
these the great majority are 
eatable by man or some 
of the lower animals, 
and oftentimes the 
I II III 
Fie. 148. Barbs 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-ticks 
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 botany, and of zodlogy 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 
