To G. H. K. Thwaites   30 March [1863]1

Down. | Bromley. | Kent. S.E.

March 30th

My dear Mr Thwaites

I thank you most cordially for the specimens which have interested me exceedingly.2 The Sethia is a beautiful case of what I shall call “reciprocal dimorphism”: unfortunately all the anthers were knocked off the long-styled, so I could not compare pollen, except from a bud in which pollen was not mature, & I dare not trust my measurements.3 If you were to watch insects visiting these flowers I would wager that you would see body dusted by long stamens, & probosis by short anthers; & the object of unequal length of the alternate stamens is to get pollen on to proboscis from more than a pair of anthers; in short to rake them. I judge this from what I have seen in Lythrum.4 Are there any Lythraceæ in Ceylon; you would be likely to find three forms, reciprocally related in sexual functions, in this order; & with two kinds of pollen in each flower. If you observe any more facts, I shd. be grateful for information & specimens. I have also been very glad to see the Limnanthemum: it, also, is a very pretty case.5 I have got a hot-house: could I grow it? & if so, could you send me seed?6

Any flower with half anther of one colour & half of other colour (if not due to abortion of one set) probably indicates dimorphism or trimorphism.—7

I much wish to experiment on one plant in each order.— Sethia I presume is a tree.

I will soon send you a little paper on dimorphism of Linum.—8

Thank you for telling me about Discospermum; it is an important fact.—9

You have hit the nail on the head in supposing that I am interested about galls (& what curious ones those are that you have sent me!); but I unfortunately know hardly anything about them; nor do I know where I can find any full account. The subject is most curious, & I have often reflected on it, & at one time thought I would attempt a series of experiments. It is truly wonderful what a change a little poison or irritation has effected, & effected in so diversified a manner.—10

With respect to the curious specimens, which you so kindly have sent me of Gomphia & Lasemia, I do not know what to think.11 Are they not the effect of insect puncture or disease, like those we see on our Birch-trees? I shd. fear to class them with what gardeners’ call “sports” or bud variation. Can you illuminate me?

With cordial thanks | Dear Thwaites | Yours very sincerely | C. Darwin

1
The year is established by the relationship between this letter and the letter from G. H. K. Thwaites, 17 February 1863.
2
At CD’s request, Thwaites had sent CD specimens of the dimorphic flowers of Sethia acuminata (a synonym of Erythroxylum moonii) and Limnanthemum indicum (a synonym of Nymphoides indica, water snowflake) with his letter to CD of 17 February 1863. See also letter to J. D. Hooker, [29 March 1863].
3
A note in DAR 110: B28, dated 29 March 1863, records CD’s observations on Thwaites’s dried Sethia specimens. CD published his observations, including an estimate of the relative size of pollen from the two forms of flower, in Forms of flowers, p. 122.
4
CD had begun experimenting on the trimorphic plant Lythrum salicaria in 1862 (see Correspondence vol. 10); he repeated this explanation of the purpose of the two lengths of stamens in Sethia in Forms of flowers, p. 122.
5
CD’s undated observational notes on these specimens are in DAR 110: B9–10. He published his observations in Forms of flowers, p. 116.
6
Thwaites sent CD seed of Limnanthemum with his letter of 8 June 1863.
7
CD had begun to consider the possibility that the occurrence of differently coloured anthers or pollen in the same or in different flowers of the same species might be ‘a safe guide to dimorphism’ (see Correspondence vol 10, letter to J. D. Hooker, 22 [August 1862] and n. 14).
8
CD’s paper, ‘Two forms in species of Linum’, was read before the Linnean Society on 5 February 1863. It was published in the number of the Journal of the Proceedings of the Linnean Society (Botany) that was issued on 13 May 1863 (General index to the Journal of the Linnean Society, p. vi). However, CD obtained a number of offprints of the paper in mid-April for distribution to those he thought would be interested; Thwaites’s name appears on CD’s presentation list (see Correspondence vol. 11, Appendix IV).
10
Thwaites apparently discussed this subject in the missing portion of his letter to CD of 17 February 1863. CD discussed galls in a section of Variation dealing with the ‘direct and definite action of the external conditions of life’ (Variation 2: 282–4). He observed of the specimens Thwaites sent him: ‘some were as symmetrical as a composite flower when in bud, others smooth and spherical like a berry; some protected by long spines, others clothed with yellow wool formed of long cellular hairs, others with regularly tufted hairs’ (Variation 2: 282).
11
In his letter to Thwaites of 29 December [1862] (Correspondence vol. 10), CD had asked Thwaites for instances of what he termed ‘bud-variations’. The part of Thwaites’s reply dealing with this subject has not been found (see letter from G. H. K. Thwaites, 17 February 1863); however, it appears that Thwaites provided specimens of Lesemia and Gomphia exhibiting what he considered to be ‘bud-variations’.

Manuscript Alterations and Comments

1.7 of the alternate stamens] interl
1.10 in sexual functions,] interl
1.11 more] above del ‘unus’
1.14 seed?] ‘?’ over ‘:’
2.1 Any flower … trimorphism.— 2.2] added
2.1 anther] after del ‘stam’

Please cite as “DCP-LETT-4067,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-4067