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Darwin Correspondence Project

From G. H. K. Thwaites   24 September 1863

Peradenia, Ceylon

24th Sept 1863

My dear Darwin,

Very very many thanks for the capital photograph of your excellent self;1 I value it greatly; it recalls to my memory so vividly and pleasantly the delightful day I spent with you and our dear friends Hooker and Harvey at Nuneham many years ago.2

I am glad you were pleased with the flowers of the Cassia:3 my friend Mr. Glenie is so delighted at having been able to communicate something to interest you that he promises to observe carefully the changes that take place in the flowers of the different species of Cassia during the time they are expanded.4 With reference to another species of Cassia (C. Roxburghii, DC.)5 he writes me “We have been examining the C. Roxburghii of late carefully, and find in it, as well as in C. Fistula, a peculiarity though not of the same marked nature, in the anthers.— The 3 upper appear to be abortive;—the middle 4 open by pores only; the lower 3 (the longest) open by pores and by clefts at the base of the lobes”

I will collect for you and send you as soon as I can, flowers of all the Cassias and other Cæsalpinieæ I can get here. It seems likely to me that the careful study of the differences inter se of the closely allied forms or species of one group, and the comparison of these with corresponding differences in other groups, will be one of the modes of iluminating the law which has operated in bringing about these differences, whether it be that of natural selection or of a law operating with it or independently of it; for such a vast period of time seeming to be a necessary element in the process, there would appear to be slight hope of direct experiment (in selection) leading to any result beyond what we see in the races of dogs, or of other domestic animals producing fertile crosses. But do these fertile crosses between very dissimilar races shew any tendency to degenerate or disappear after a certain number of generations? The mixed race here, between the Portuguese and Cinghalese, are not a healthy set of people judging from those I have had anything to do with, and they certainly will not compare in symmetry or good looks with either of the original races.

Believe me always | My dear Darwin | Most sincerely yours | G. H. K. Thwaites.

CD annotations

1.1 Very … ago. 1.4] crossed pencil
On cover: ‘Grdation | Cassiapencil 6


At Thwaites’s request, CD had sent a photograph of himself with his letter to Thwaites of 29 July [1863].
Joseph Dalton Hooker and William Henry Harvey. CD and Thwaites first met at the annual meeting of the British Association for the Advancement of Science held in Oxford in 1847 (see Correspondence vol. 5, letter to G. H. K. Thwaites, 10 December 1855); during the meeting an excursion was made to Nuneham, a beauty spot near Oxford (see Correspondence vol. 4, letter to J. S. Henslow, [26 September 1849]).
The flower of Cassia fistula enclosed in the letter from G. H. K. Thwaites, 8 June 1863, had been collected by Samuel Owen Glenie; Thwaites also sent CD Glenie’s covering letter describing the specimen.
Thwaites enclosed with this letter a packet containing a pressed flower, labelled ‘Cassia Roxburgii, DC.’. The flower is in DAR 48: 74. ‘DC’ is the botanical abbreviation for Augustin Pyramus de Candolle, who named Cassia roxburghii in 1825 (Candolle and Candolle 1824–73, 2: 489).


Candolle, Augustin Pyramus de and Candolle, Alphonse de. 1824–73. Prodromus systematis naturalis regni vegetabilis, sive enumeratio contracta ordinum generum specierumque plantarum huc usque cognitarum, juxta methodi naturalis normas digesta. 19 vols. Paris: Treuttel & Würtz [and others].

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 26 vols to date. Cambridge: Cambridge University Press. 1985–.


Sends information on the flowers of Cassia roxburghii; will send flowers of all the species of Cassia for CD to study with a view to discovering the law which operates to bring about the differences.

Letter details

Letter no.
George Henry Kendrick Thwaites
Charles Robert Darwin
Sent from
Source of text
DAR 48: 74
Physical description
4pp † enc

Please cite as

Darwin Correspondence Project, “Letter no. 4303,” accessed on 23 October 2019,

Also published in The Correspondence of Charles Darwin, vol. 11