From George Henry Kendrick Thwaites   17 February 1863

Peradenia, Ceylon

17th Feby 1863

My dear Mr. Darwin,

It gives me very sincere pleasure to be able to gratify the wishes expressed in your welcome and interesting letter of the 29th. Decr.1 and let me, in the first place, thank you for the information respecting the dimorphism of Cinchona. I shall not fail to act upon it when our plants come into flower.2

Dimorphism would appear to be common in the Rubiaceæ, & there would seem to be every degree of it as regards development of stamens & pistil in the respective flowers: In the genus Discospermum the ♂ flowers are always barren, though the ovary contains about 2 abortive ovules in each loculis, & it must have been from the examination of one of these that the genus Diplospora (synonymous with Discospermum) was constituted; The ovary of the ♀ flower contains several ovules.3

I send you in weak spirits the two forms of flowers of Limnanthemum Indicum, Enum.—p. 2054 (hand Grisebr)—L. Kleinianum & L. Wightianum, Grisebr.)5 The pollen is alike in both forms diagram and I find the same number of ovules (70–80) in the ovaries of both. I have not had an

incomplete6

CD annotations

1.1 It gives … flower. 1.4] crossed ink; ‘General Cinchona’ added blue crayon; ‘Keep gradation’ added red crayon; ‘On into Dioiceous’ added blue crayon
2.3 In … constituted; 2.6] scored brown crayon
2.6 The ovary … ovules. 2.7] ‘more in Cinchona, as it does not follow at all [the two forms that [illeg] render [same] plants wd [illeg del] diœcious]’7 added ink
3.1 I send … had an 3.4] crossed pencil
Top of letter: ‘The meaning of different positions of anther in Sethia, is to [over ‘the’] rake short anther on proboscis; whereas body wd be dusted by long-anthers.—’ ink, del pencil; ‘Rubiaceæ’ pencil; ‘Limnanthemum’ pencil, del pencil
1
In his letter to Thwaites of 29 December [1862] (Correspondence vol. 10), CD asked for examples of bud-variation; CD was writing a draft of chapter 11 of Variation, ‘On bud-variation, and on certain anomalous modes of reproduction and variation’ (Variation 1: 373–411), which he began on 21 December 1862 (Correspondence vol. 10, Appendix II). CD was seeking information on the question of whether introduced flowers from different climates were particularly apt to produce bud-variations. CD also asked Thwaites to repeat the names of the two genera (Sethia and Limnanthemum) that he had mentioned in an earlier letter as being dimorphic (Correspondence vol. 10, letter from G. H. K. Thwaites, 15 May 1862), and requested him to send specimens of the different forms (see n. 5, below, and letter to G. H. K. Thwaites, 30 March [1863]).
2
In his letter to Thwaites of 15 June [1862] (Correspondence vol. 10), CD noted that some trees of the genus Cinchona had long pistils and others had short pistils. CD stressed the probable importance of reciprocal pollination between the two forms of Cinchona, in order to get good seed and seedlings. He asked Thwaites, who was superintendent of the Peradeniya botanic gardens, Ceylon, to experiment with crossing the two forms, adding: ‘The growth of Cinchona is so important for Mankind, that I am sure you will excuse my making this suggestion.’ Cinchona was a source of quinine, which was widely used to treat malaria. In his letter to Thwaites of 29 December [1862] (ibid.), CD confirmed what he had previously written regarding dimorphism in Cinchona, adding that he now had ‘proof that some of these dimorphic plants are absolutely sterile with their own-form pollen’.
3
Cinchona, Discospermum, and Diplospora are all members of the family Rubiaceae. Thwaites’s information on dimorphism in Rubiaceae is cited in Forms of flowers, p. 286.
4
The reference is to Enumeratio plantarum Zeylaniae: an enumeration of the Ceylon plants (Thwaites 1858–64).
5
CD had asked Thwaites to send him specimens of dimorphic plants (see n. 1, above). Limnanthemum indicum, L. kleinianum, and L. wightianum were named by the German botanist August Heinrich Rudolph Grisebach (Grisebach 1845, p. 139); L. kleinianum and L. wightianum are synonyms for L. indicum (Index Kewensis). CD’s notes on these specimens are in DAR 110: B9–10; see also Forms of flowers, p. 116.
6
For an indication of the contents of the missing portion of the letter, see CD’s annotations, and the letter to G. H. K. Thwaites, 30 March [1863].
7
CD noted that, as one of the two forms of Discospermum was always barren, the species appeared to be strictly dioecious, and did not come within his definition of heterostyly (see Forms of flowers, p. 286).

Please cite as “DCP-LETT-3994,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-3994