INSECTS IN RELATION TO PLANTS 



257 



FIG. 250. 



purpose of catching insects. The stout hairs of these leaves 

 end each in a globular knob, which secretes a sticky fluid. 

 When a fly alights on one of these leaves the hairs bend over 

 and hold the insect ; then a fluid analogous to the gastric juice 

 of the human stomach exudes, digests the 

 albuminoid substances of the insect and 

 these are absorbed into the tissues of the 

 leaf; after which the tentacles unfold 

 and are ready for the next insect visitor. 

 The Venus's flytrap is another well- 

 known example; the trap, formed from 

 the terminal portion of a leaf, consists of 

 two valves, each of which bears three 

 trigger-like bristles, and when these are 

 touched by an insect the valves snap to- 

 gether and frequently imprison the insecc, 

 which is eventually digested, as before. 

 In the common pitcher-plants, the pitcher, 

 fashioned from a leaf, is lined with down- 

 ward pointing bristles, which allow an 

 insect to enter but prevent its escape. 

 The bottom of the pitcher contains water, 

 in which may be found the remains 

 of a great variety of insects which 

 have drowned. There are even nectar 

 glands and conspicuous colors, presum- 

 ably to attract insects into these traps, 

 where their decomposition products are 

 more or less useful to the plant. In 

 Pinguicula the margin of a leaf rolls 

 over and envelops insects that have 

 been caught by the glandular hairs of the upper surface 

 of the leaf, a copious secretion digests the softer portions of 

 the insects, and the dissolved nitrogenous matter is absorbed 

 into the plant. Utricnlaria has little bladders which entrap 

 small aquatic insects. These plants are only partially depend- 

 18 



Fructifying sprouts of 

 a fungus, Cordyceps rat- ?- 

 nelii, arising from the 

 body of a white grub, 

 Lachnosterna. Slightly 

 reduced. After RILEY. 



