go Elementary Botany 



either of these plants, we find that their upper surfaces are 

 covered with glandular hairs which, when touched, exude a few 

 drops of a sticky liquid which adheres to the fingers, and will 

 be drawn out into a fine thread. 



If an insect settles upon the leaf it becomes arrested, and 

 gradually the leaf folds over, enclosing it. It thus remains 

 closed for a short time, and on opening again there is found 

 merely the outer shell of the insect, all the nutritive part having 

 been absorbed by the plant. The leaf seems to contain a sub- 

 stance analogous to, if not identical with, the pepsine of the 

 animal stomach, which possesses the power of rendering nitro- 

 genous substances soluble. Other carnivorous plants have the 

 same power of absorbing organic food materials by their leaves 

 in various ways. 



7. In some cases the leaves act as organs of support. — 

 We have already seen that parts of the leaf may be converted 

 into tendrils (figs. 93 and 104), thus twining round the organ of 

 support and sustaining the stem. In the Tropaeolum the leaf- 

 stalk itself twines and supports the plant. 



Parasites.— It has been noted (page 34) that some plants 

 obtain their food through the medium of others. Such plants 

 are known as parasites. We may divide them under three 

 heads. 



(a) Semi-Parasites. — These can obtain some food from the 

 soil, but not sufficient to enable them to grow in a luxuriant 

 manner. 



If some seeds of Yellow Rattle be allowed to germinate in 

 earth they will grow, but the plants will not be fully developed. 

 If, however, the seeds be sown amongst some grass, strong, well- 

 developed Rattles will be obtained. The Rattle sends its roots 

 into the roots of the grass and draws sap out of them, which is 

 afterwards elaborated in its own leaves. 



{b) Green parasites. — Mistletoe (fig. 61s) is a type of this 

 class. It cannot obtain any nourishment for itself out of the 

 soil, and has to depend entirely upon the tree into whose stem 

 it sends its roots. At the same time its leaves contain chloro- 

 phyll, and hence it can decompose the carbon dioxide of the 

 atmosphere, and assimilate food for itself. 



