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. From 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. Inseetivorous Plants.— 
These are green plants which, 
by a special mechanism, en- 
trap and digest small insects. 
The British representatives Fic. 43.—MisTLEeroE aTTacHED 
are: By Havstor1a (a) TO BRANCH 
. oF A TREE (5), BoTH SEEN IN 
(a) Drosera (three species), SECTION. 
the sundew, a bog-plant. 
(6) Pinguicula (four species), the butterwort, 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. Small 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 
19 
