122 ESSENTIALS OF BOTANY 



and very generally succeeds in capturing the fly or other 

 insect which has sprung it. The imprisoned insect then 

 dies and is digested, somewhat as in the case of those 

 caught by the sundew, after which the trap reopens and is 

 ready for fresh captures. 



141. Object of catching Animal Food. — It is easy to 

 understand why a good many kinds of plants have taken 

 to catching insects and absorbing the digested products. 

 Carnivorous, or flesh-eating, plants belong usually to one 

 of two classes as regards their place of growth : they are 

 bog-plants or air-plants. In either case their roots find it 

 difficult to secure much nitrogen-containing food, — that is, 

 much food out of which proteid material can be built up. 

 Animal food, being itself largely proteid, is admirably 

 adapted to nourish the growing parts of plants, and those 

 which could develop insect-catching powers would starid 

 a far better chance to exist as air-plants or in the thin, 

 watery soil of bogs than plants which had acquired no 

 such resources. 



142. Destruction of Plants by Animals All animals 



are supported directly or indirectly by plants. In some 

 cases the animal secures its food without much damage 

 to the plant on which it feeds. Browsing on the lower 

 branches of a tree may do it little injury, and grazing 

 animals, if not numerous, may not seriously harm the 

 pasture on which they feed. Fruit-eating animals may 

 even be of much service by dispersing seeds. But seed- 

 eating birds and quadrupeds, animals which, like the hog, 

 dig up fleshy roots, rootstocks, tubers, or bulbs, and eat 

 them, or animals which, like the sheep, graze so closely as 

 to expose the roots of grasses or even of forest trees to be 

 parched by the sun, destroy immense numbers of plants. 



