The Life and Letters of Darwin, Volume 2 HTML version

Climbing And Insectivorous Plants
[My father mentions in his 'Autobiography' (volume i.) that he was led to take up the
subject of climbing plants by reading Dr. Gray's paper, "Note on the Coiling of the
Tendrils of Plants." ('Proc. Amer. Acad. of Arts and Sciences,' 1858.) This essay seems to
have been read in 1862, but I am only able to guess at the date of the letter in which he
asks for a reference to it, so that the precise date of his beginning this work cannot be
In June 1863 he was certainly at work, and wrote to Sir J.D. Hooker for information as to
previous publications on the subject, being then in ignorance of Palm's and H. v. Mohl's
works on climbing plants, both of which were published in 1827.]
Down [June] 25 [1863].
My dear Hooker,
I have been observing pretty carefully a little fact which has surprised me; and I want to
know from you and Oliver whether it seems new or odd to you, so just tell me whenever
you write; it is a very trifling fact, so do not answer on purpose.
I have got a plant of Echinocystis lobata to observe the irritability of the tendrils
described by Asa Gray, and which of course, is plain enough. Having the plant in my
study, I have been surprised to find that the uppermost part of each branch (i.e. the stem
between the two uppermost leaves excluding the growing tip) is CONSTANTLY and
slowly twisting round making a circle in from one-half to two hours; it will sometimes go
round two or three times, and then at the same rate untwists and twists in opposite
directions. It generally rests half an hour before it retrogrades. The stem does not become
permanently twisted. The stem beneath the twisting portion does not move in the least,
though not tied. The movement goes on all day and all early night. It has no relation to
light for the plant stands in my window and twists from the light just as quickly as
towards it. This may be a common phenomenon for what I know, but it confounded me
quite, when I began to observe the irritability of the tendrils. I do not say it is the final
cause, but the result is pretty, for the plant every one and a half or two hours sweeps a
circle (according to the length of the bending shoot and the length of the tendril) of from
one foot to twenty inches in diameter, and immediately that the tendril touches any object
its sensitiveness causes it immediately to seize it; a clever gardener, my neighbour, who
saw the plant on my table last night, said: "I believe, Sir, the tendrils can see, for
wherever I put a plant it finds out any stick near enough." I believe the above is the
explanation, viz. that it sweeps slowly round and round. The tendrils have some sense, for
they do not grasp each other when young.
Yours affectionately,