Ɛpsilon

From W. T. Thiselton-Dyer   6 December 1873

10 Gloucester Road, Kew

Dec 6. 1873

Dear Mr Darwin

Your Cassia is one well known in cultivation and it passes under the name of Cassia floribunda, Hort.1 It is curious how difficult it usually is to determine the species to which cultivated plants belong even when there is little reason to suspect that they have deviated materially from the stock originally introduced.

I asked Mr Bentham, who has made a special study of the genus, what he had done with C. floribunda and he told me that it came very near to C. lævigata, Willd. and was probably one of a series of garden hybrids between that and C. tomentosa, Linn. which have originated in France from whence we get the plant.2 It is no doubt what Lindley figured with rather paler flowers as C. Herbertiana in the Bot. Reg t. 1422.3

That the young leaves of the Cassia should respond to syringing is a most novel and striking fact.4

I wonder whether the closing of the flower of the Pimpernel and many others in cloudy weather is connected with the protection of their process of fertilisation from interference by rain.5

I was glad to look into the question of the Cassia because it is my business to know such things. Apart from that it is no small honour to make any contribution however small to the progress of your newest edifice

Believe me | Yours very truly | W. T. Thiselton Dyer

CD annotations

2.1 I asked … plant. 2.4] ‘The common Greenhouse Bush chiefly observed by me.—’ added ink
2.2 C. lævigata,] underl red crayon
2.3 C. tomentosa, 2.4] underl red crayon
Top of letter: ‘Name’ red crayon
1
See letter to W. T. Thiselton-Dyer, 4 December 1873. Cassia floribunda is now Senna floribunda.
2
George Bentham had published a revision of the genus Cassia in the Transactions of the Linnean Society of London (Bentham 1869). CD’s annotated copy is in the collection of unbound journals in the Darwin Library–CUL. Bentham had placed C. floribunda(a synonym of Senna floribunda) in synonymy with C. laevigata (now Senna septemtrionalis) and next to C. tomentosa (now S. multiglandulosa; see Bentham 1869, pp. 527–8), indicating that he considered the two species to be closely related.
3
John Lindley described Cassia herbertiana in Edwards’s Botanical Register 17 (1831): pl. 1422. CD added Thiselton-Dyer’s information on C. floribunda to Movement in plants, p. 369.
5
The scarlet pimpernel, Angalis arvensis, is sometimes known as poor man’s weather glass or shepherd’s clock because the flowers close in cloudy weather before rain.

Please cite as “DCP-LETT-9174,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-9174