160 The Romance of Wild Flowers 
The question naturally arises, Why should a plant 
develop a trait so characteristic of animal life, and 
so thoroughly opposed to the general notions of plant- 
life? The answer is to be found in the habitat of 
the plant. We have seen, in considering the Pea- 
tribe, that nitrogen is so hable to be washed out of 
the soil that we should scarcely expect to find much 
of it where a spring or the drainage from the moors 
above comes down unceasingly. In the latter case 
there would probably be a small percentage of nitrogen 
washed down, but the sphagnum would be most likely 
to secure it, and the Sundews have therefore given 
up competing for it through their roots, and instead 
have so modified their leaves that these organs are able 
to obtain it for them. It is a noteworthy fact that, 
though this carnivorous habit has been developed in 
plants belonging to families unrelated to each other, 
they all agree in the fact that they grow in bogs and 
ditches, or places where their roots are similarly 
steeped in water; and it is reasonable to suppose that 
this similarity of habitat has led the plants to adopt 
like means to obtain the necessary nutrition. Such a 
power could not be so well exercised if the specialisa- 
tion of the leaf-form were not correlated with a 
remarkable degree of sensitiveness. This exquisite 
sense is restricted to the glandular tips of the 
tentacles, and it is not until some portion of the 
insect has come into actual contact with this that 
the neighbouring tentacles know anything of the 
matter. But no sooner does the leg of a fly press 
through the globule of mucilage and touch the 
gland itself than the excitement is communicated 
through the tentacle to the leaf substance, and so to 
