Plants That Feed on Insects. 21 
nitrogeneous matter, the two lobes retain their inwardly con- 
cave form until they re-expand. The re-expansion, when no 
organic matter is enclosed, varies according to circumstances, 
a leaf in one instance being fully re-expanded in thirty-two 
hours. 
But the lobes, when soluble nitrogeneous matter is included, 
instead of remaining concave, thus containing within a con- 
cavity, slowly press closely together throughout their entire 
breadth, and as this takes place the margins gradually become 
a little everted, so that the spikes, which at first intercrossed, 
at last project in two parallel rows. So firmly do they become 
pressed together that, if any large insect has been caught, a 
corresponding projection is clearly visible on the outside of 
the leaf. When the two lobes are thus completely closed, 
they resist being opened, as by a thin wedge driven with 
astonishing force between them, and are generally ruptured 
rather than yield. If not ruptured, they close again with 
quite a loud flap. The slow movement spoken of, excited 
by the absorption of diffused animal matter, suffices for its 
final purpose, whilst the movement brought on by the touch- 
ing of one of the sensitive filaments is rapid, and thus indis- 
pensable for the capturing of insects. 
Leaves remain shut for a longer time over insects, especially 
if the latter are large, than over meat. In many instances 
where they have remained for a long period over insects 
naturally caught, they were more or less torpid when they 
reopened, and generally so much so during many succeeding 
days that no excitement of the filaments caused the least 
movement. Vigorous leaves will sometimes devour prey 
several times, but ordinarily twice, or, quite often, once is 
enough to render them unserviceable. 
What purpose the marginal spikes, which form so conspicu- 
ous a feature in the appearance of the plant, subserve was 
unknown until the genius of Darwin solved the mystery. It 
was he that showed that elongated spaces between the spikes, 
varying from one-fifteenth to one-tenth of an inch in breadth 
