844 FOUNDATIONS OF BOTANY 
Fig. 241, terminate in a hinged portion which is surrounded 
by a fringe of stiff bristles. On the inside of each half 
of the trap grow three short hairs. The trap is so sensi- 
tive that when these hairs are touched it closes with a jerk 
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. 
411. Object of catching Animal Food. —JIt 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 stand 
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. 
