INSECTIVOROUS PLANTS 



129 



is inefficient, and little or no starch is formed in the leaves. 

 The colour is a dull yellowish-green, and the chlorophyll 

 is probably on the verge of extinction. The branches 

 are repeatedly forked, and each branch bears at its 

 extremity two tough evergreen leaves, and no more. 

 The terminal bud between the leaves always bears an 

 inflorescence, which later on in the year is represented 

 in the female plants by a number of white viscous berries. 

 When these fall, vegetative growth is continued from 

 buds which develop in the axils of the two leaves, and in 

 this way a regular system of 

 forking results. Prom these 

 facts it is evident that the 

 mistletoe is well on its way to 

 become a colourless, leafless 

 parasite. In total parasites 

 both pigment and leaves 

 vanish or degenerate through 

 disuse. In Nature everything 

 which has outlived its useful- 

 ness tends, sooner or later, to 

 disappear. 



3. Insectivorous Plants. — 

 These are green plants which, 

 by a special mechanism, en- 

 trap and digest small insects. 

 The British representatives 

 are : 



(a) Drosera (three species), 

 the sundew, a bog-plant. 



(&) Pinguicula (four species), thebutterwort, a bog-plant. 



(c) Utricularia (four species), the bladderwort, a sub- 

 merged aquatic. 



(a) Drosera. — D. rotundifolia and D. longifolia (Fig. 44) 

 occur in peaty bogs. They are small rosette-plants, and 

 the leaves are furnished with a multitude of stalked glands 

 or tentacles, which are reddish in colour, and crowned each 

 with a glistening globule of gum. SmaU insects, chiefly 

 flies, attracted possibly by the coloured and glistening 

 tentacles, alight upon the leaf, and are held fast by the 

 gum, caught, as it were, in a kind of birdlime. The leaf 

 is sensitive, and the contact of the insect sends an impulse 

 through it ; the edges rise, the tentacles curl over towards 



Q 



Fig. 43. — Mistletoe attaohed 

 BY Haustohia (a) TO Branch 

 OF A Tbeb (6), Both seen in 

 Sbotioit. 



