Insectivorous Plants | Page 3

the roots.
During the summer of 1860, I was surprised by finding how large a
number of insects were caught by the leaves of the common sun-dew
(Drosera rotundifolia) on a heath in Sussex. I had heard that insects
were thus caught, but knew nothing further on the subject.* I
* As Dr. Nitschke has given ('Bot. Zeitung,' 1860, p. 229) the

bibliography of Drosera, I need not here go into details. Most of the
notices published before 1860 are brief and unimportant. The oldest
paper seems to have been one of the most valuable, namely, by Dr.
Roth, in 1782. There is also an interesting though short account of the
habits of Drosera by Dr. Milde, in the 'Bot. Zeitung,' 1852, p. 540. In
1855, in the 'Annales des Sc. nat. bot.' tom. iii. pp. 297 and 304, MM.
Groenland and Trcul each published papers, with figures, on the
structure of the leaves; but M. Trcul went so far as to doubt whether
they possessed any power of movement. Dr. Nitschke's papers in the
'Bot. Zeitung' for 1860 and 1861 are by far the most important ones
which have been published, both on the habits and structure of this
plant; and I shall frequently have occasion to quote from them. His
discussions on several points, for instance on the transmission of an
excitement from one part of the leaf to another, are excellent. On
December 11, 1862, Mr. J. Scott read a paper before the Botanical
Society of Edinburgh, [[page 2]] which was published in the
'Gardeners' Chronicle,' 1863, p. 30. Mr. Scott shows that gentle
irritation of the hairs, as well as insects placed on the disc of the leaf,
cause the hairs to bend inwards. Mr. A.W. Bennett also gave another
interesting account of the movements of the leaves before the British
Association for 1873. In this same year Dr. Warming published an
essay, in which he describes the structure of the so-called hairs, entitled,
"Sur la Diffrence entre les Trichomes," &c., extracted from the
proceedings of the Soc. d'Hist. Nat. de Copenhague. I shall also have
occasion hereafter to refer to a paper by Mrs. Treat, of New Jersey, on
some American species of Drosera. Dr. Burdon Sanderson delivered a
lecture on Dionaea, before the Royal Institution published in 'Nature,'
June 14, 1874, in which a short account of my observations on the
power of true digestion possessed by Drosera and Dionaea first
appeared. Prof. Asa Gray has done good service by calling attention to
Drosera, and to other plants having similar habits, in 'The Nation' (1874,
pp. 261 and 232), and in other publications. Dr. Hooker, also, in his
important address on Carnivorous Plants (Brit. Assoc., Belfast, 1874),
has given a history of the subject. [page 2]
gathered by chance a dozen plants, bearing fifty-six fully expanded
leaves, and on thirty-one of these dead insects or remnants of them

adhered; and, no doubt, many more would have been caught afterwards
by 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]
secondly, the power possessed by the leaves of rendering soluble or
digesting nitrogenous substances, and of afterwards absorbing them;
thirdly, the changes which take place within the cells of the tentacles,
when the glands are excited in various ways.
It