From Thomas Henry Farrer   17 May 1868

3 Gloucester Terrace | Regent’s Park.

17 May/68

My dear Mr Darwin

Will you think me very presumptuous or very troublesome if, having spent a Sunday morning with your fascinating book over a handful of Fly Orchises I venture to raise a question about a statement in it which I cannot verify. You say that the pollinia of this Orchis when removed do not bend down as they do in Orchis mascula &c but that the original bend in the caudicle answers the same purpose.1 They certainly do not bend so quickly or so obviously, but with a good many I have tried I think they certainly do bend.

Taking them out with a needle and putting it down at once so that it may not be turned I find that the distance of the caudicle at the point (a) from the needle, which at first is considerable, always diminishes after a few minutes until the exterior angle of the caudicle at (a) rests upon the needle.2 I think too, but am not sure, that whilst the angle which the base of the caudicle makes with the needle diminishes the pollen mass turns upwards so as to keep it perpendicular to the needle. The result is that when the needle is again inserted into a flower, the side of the pollen mass nearest to the point of the needle will just catch the stigma, which it would not have done in its original position.

I may be & probably am all wrong—but I know you do not despise weak vessels. Pray do not trouble yourself to answer.

By the way, as I am writing, I will mention what my brother told me the other day after reading your book, though I daresay you know it already.3 He used in young & evil days to see a good deal of dog fanciers—and he says that it was a fixed idea with them that there was a constant tendency in most of the fancy breeds of dogs to revert to a lightish brown or liver colour—e.g. that in the case of black & tan terriers, which are always bred for the black & tan colour, there would generally be one wholly brown pup in every litter. He speaks of their impressions and only to a small extent of his own experience.

Believe me | Very truly yours | T H Farrer

Charles Darwin Esq FRS

[Enclosure]

diagram
1
CD discussed the bending of the caudicle of the pollinium in Orchis mascula in Orchids, pp. 15–16; he discussed the double bend in the caudicle of the fly ophrys, Ophrys muscifera, and the inability of the caudicle to bend from that position, in Orchids, pp. 55–6. In Orchids 2d ed., p. 46, CD wrote: ‘I formerly thought that it [the caudicle] was incapable of any movement, but have been convinced by Mr. T. H. Farrer of my error.’ CD also noted Farrer’s observations in ‘Fertilization of orchids’, p. 144 (Collected papers 2: 141). Ophrys muscifera is a synonym of Ophrys insectifera.
2
CD’s diagram in Orchids, p. 15, shows that when the pollinium is extracted from Orchis mascula by a long narrow instrument like a needle or, in his case, a pencil, the viscid disc at the base of the caudicle of the pollinium sticks to the surface of the pencil so that the caudicle is perpendicular to the pencil. Over time, the caudicle bends from its base so that it becomes almost parallel to the pencil.
3
Farrer refers to Variation, and to either William James Farrer or Frederick Willis Farrer, his brothers.

Please cite as “DCP-LETT-6178,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-6178