236 



TEXTBOOK OP BOTANY 



branched. The thorns of the black locust are merely 

 stipules ; and similar thorns are borne by various acacias 

 and euphorbias (Fig. i4i),' especially by species that Hve 

 in warm, dry regions. A tendril, too, may be a branch, a 

 root, a leaf, or part of a leaf. Sometimes, as in some rela- 

 tives of the sweet pea, a whole leaf develops into a tendril. 

 More commonly, as in the peas, sweet pea, and vetches, 



the tendrils are merely some of 

 the last leaflets, the lower parts 

 of each leaf being of the ordinary 

 form. In some Indian grasses, 

 the midrib grows out beyond the 

 blade in the form of a tendril. 

 Sometimes stipules become ten- 

 drils, as in various species of 

 Smilax. Sometimes, as in Clema- 

 tis and in climbing varieties of 

 Tropaeolum (the common "nas- 

 turtium"), the leaf-stalk acts as 

 a tendril, still bearing at its 

 outer end a blade of the usual 

 form. 



252. Insect-Catching Leaves. 

 — The leaves of a few plants 

 have taken on very odd forms 

 that make them traps for in- 

 sects. These plants, although they have chlorophyl and 

 can manufacture carbohydrates for themselves, use the softer 

 parts of the insects' bodies for food. Such use of animal 

 food is possible to but few green plants, most of which, as 

 we have seen, can use the materials of animals' bodies only 

 after they have been broken down, mainly by the action of 

 bacteria, into much simpler substances. 



Among the best known of the insect-catching plants is the 

 " pitcher plant " of Canada and the eastern United States 



Fig. 141. — Euphorbia splen- 

 dens, a plant whose stipules 

 take the form of thorns. 



