these same leaves, and still more by those as yet not expanded. On one
plant all six leaves had caught their prey; and on several plants very
many leaves had caught more than a single insect. On one large leaf I
found the remains of thirteen distinct insects. Flies (Diptera) are
captured much oftener than other insects. The largest kind which I have
seen caught was a small butterfly (Caenonympha pamphilus); but the Rev.
H.M. Wilkinson informs me that he found a large living dragon-fly with
its body firmly held by two leaves. As this plant is extremely common
in some districts, the number of insects thus annually slaughtered must
be prodigious. Many plants cause the death of insects, for instance the
sticky buds of the horse-chestnut (Aesculus hippocastanum), without
thereby receiving, as far as we can perceive, any advantage; but it was
soon evident that Drosera was [page 3] excellently adapted for the
special purpose of catching insects, so that the subject seemed well
worthy of investigation.

The results have proved highly remarkable; the more important ones
being--firstly, the extraordinary

FIG. 1.* (Drosera rotundifolia.) Leaf viewed from above; enlarged four
times.

sensitiveness of the glands to slight pressure and to minute doses of
certain nitrogenous fluids, as shown by the movements of the so-called
hairs or tentacles;

* The drawings of Drosera and Dionaea, given in this work, were made
for me by my son George Darwin; those of Aldrovanda, and of the several
species of Utricularia, by my son Francis. They have been excellently
reproduced on wood by Mr. Cooper, 188 Strand. [page 4]