To Daniel Oliver 11 September 1
Down. | Bromley. | Kent. S.E.
My dear Sir
I was pleased to see your handwriting again, & sincerely hope that you are quite recovered from your long illness. Take warning from me & do not work too hard.— Very many thanks for information about P. ciliata & var.—2 I was sure it could not be an ordinary variety; it differed too much & I was utterly perplexed what to do about it.—3 I shd. have much liked to have seen P. farinosa, but I well knew that you could not send it, else you would have done so.—4
I hate changing work & I have so many irons in the fire that I have stopped looking after Dionæa.— I return your nice sketches which make me quite envious. I do not of course mean to attempt any minute work at structure; merely a few functional observations relatively to Drosera (which alas I have resolved to put off for another year, for I have amused myself too long over Primulas & Orchids).—5
I have made out very little on Dionæa: merely that the leaf behaves very differently when a fly, or only bit of cork & nothing is caught.— When a fly is caught much acid mucous is poured out as in Drosera. And the leaf must absorb so as to perceive when it has caught a fly— The “tortoises” seem to be the secretors & absorbers & appear to me to be strictly homologous with the glands in Drosera.— It is odd that meat, flies, sol. of C. of ammonia, will not excite movement or secretion; the sensitive filament must be touched to set all in action. The sensitiveness of the filament is prettily adapted: drop of water falling on them, or strong wind through pipe produces no effect; but a touch by a woman’s Hair held with one inch length free will suffice. There is a pretty difference with Drosera: the latter does not care for a single rough touch with even a needle, but a weight left on the gland of of a grain will excite movement; & this is good for plant, for it has to clasp an insect when resting on & sticking to the gland: it would be lost labour to Drosera to close when merely touched by large insect.— In Dionæa, a far lighter single touch by mere hair causes movement; but a much greater weight, if put on delicately, may be left on the filament, without exciting movement than with Drosera.—
But I must not run on. | Pray believe me | Yours very sincerely | Charles Darwin
Has put Drosera off while amusing himself with Primula and orchids.
Dionaea is prettily adapted to weight detection.
Please cite as
Darwin Correspondence Project, “Letter no. 3251,” accessed on 24 October 2016, http://www.darwinproject.ac.uk/DCP-LETT-3251