54 



NATURAL HISTORY 



by a trail of sweet nectar secreted just outside the mouth of the 

 pitcher. Once inside, a shppery surface and incurving hairs prevent 

 egress, and the insect is soon digested by the enzymes in the fluid 

 contained inside the pitcher. Still another leaf modification with a 

 similar function is seen in the sundew (Drosera sp.). Here the leaves 

 are covered on one surface by sticky glandular hairs, which close 



The leaf of a bladder wort {Uiricu- 

 laria vulgaris). Many of its numerous 

 divisions bear bladders (6), especially 

 near the place of attachment to the 

 main leaf axis (a). Note the aper- 

 tures of the bladders (p) into which 

 small aquatic animals may crawl or 

 swim. 



The modified leaf of a sundew {Drosera 

 rotund if olia) showing the conspicuous 

 glandular hairs (g) covering the upper 

 surface, the hairs at the right having 

 caught an insect. Note that the hairs 

 are tipped by a drop of secreted liquid 

 {d), which attracts insects to the leaf and 

 also entangles them. — After Kerner. 



over the insect, hold it fast, and ultimately digest it and absorb its 

 juices. In the Venus's-flytrap (Dionaea sp.), another carnivorous 

 plant found in some parts of this country, the leaves have two sensi- 

 tive lobes provided with marginal hairs. If an insect lights on a 

 leaf, the two lobes close over it and the insect is trapped. After its 

 prey is digested, the lobes of the leaf open up and the plant is ready 

 for action again. 



Symbiosis 



The process of living together for mutual advantage is called 

 symbiosis. Plants may join forces as may animals, or in some 

 instances, plants with animals. Lichens, for example, illustrate this 



