THE FRUIT. 191 ¥ 
What reason can be given for the fact that the burdock, the 
cocklebur, the beggar-ticks, the hound’s-tongue, and many other 
common burs, are among the most persistent of weeds ? 
229. Lxplosive Fruits. — Some dry fruits burst open when 
ripe in such a way as to throw their -seeds violently about. 
Interesting studies may be made of this section in the 
common blue violet, the pansy, the wild balsam, the garden 
balsam, the crane’s-bill, the herb Robert, the witch hazel, and 
some other common plants. Thecapsuleof 
the South American sand-box tree bursts 
open when thoroughly dry with a noise like 
that of a pistol-shot. 
How are plants benefited by the explo- 
sion of the fruit ?? 
230. Uses of Fruits to the Plant. — 
Those portions of the fruit which surround 
the seeds serve to enclose the ovules during 
their period of ripening, and to protect 
them from drying up or from other injuries. 
Other kinds of service rendered by the “ies ee 
coatings or appendages of the fruit may 
have been suggested by the questions asked in some of the 
preceding sections. 
Besides the dry fruits of which some of the principal kinds 
have been mentioned, there are many kinds of stone fruits and 
Jleshy fruits, §§ 225-231. Of these the great majority are 
eatable by man or some of the lower animals, and often- 
times the amount of sugar and other food material which they 
contain is very great. It is a well recognized principle of 
botany, and of zodlogy as well, that plants and animals do 
not make 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 seeds. It is worth 
1 See Lubbock’s Flowers, Fruits, and Leaves, Chapter III. 
