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Darwin Correspondence Project

To WTThiselton-Dyer   14 July [1878]1

Down, | Beckenham, Kent. | Railway Station | Orpington. S.E.R.

July 14th

My dear Dyer

Thalia dealbata was sent me from Kew— it has flowered & after looking casually at the flowers, they have driven me almost mad & I have worked at them for a week:— it is as grand a case as that of Catasetum.2

Pistil vigorously motile, (so that whole flower shakes when pistil suddenly coils up.) when excited by a touch the two filaments produced laterally & transversely across the flower (just over the nectar) from one of the petals or modified stamens. It is splendid to watch the phenomenon under a weak power when a bristle is inserted into a young flower which no insect has visited. As far as I know Stylidium is sole case of sensitive pistil & here it is the pistil & stamens.3 In Thalia cross-fertilisation is ensured by the wonderful movement, if bees visit several flowers.

I have now relieved my mind & will tell the purpose of this note—viz if any other species of Thalia besides T. dealbata shd. flower with you, for the love of Heaven & all the Saints, send me a few in tin-box with damp moss,4

Your insane friend | Ch. Darwin


The year is established by the relationship between this letter and the letter from W. T. Thiselton-Dyer, 16 July 1878.
A plant of Thalia dealbata (powdery alligator-flag) had been sent to CD from the Royal Botanic Gardens, Kew, on 3 July 1877 (Outwards book, Archives, Royal Botanic Gardens, Kew). On 7 July 1878, CD began to investigate the mechanism developed by the flower to ensure cross-fertilisation (see letter to Francis Darwin, 7 [July 1878]. For CD’s remarks on the similar mechanism in plants in the orchid genus Casasetum, see Orchids 2d ed., p. 179.
Stylidium is the genus of trigger plants; the column (fused male and female organs) is elongated and bent, with a trigger-like action when touched.
Thalia species are native to the Americas and Africa; no other species of the genus was recorded as being sent from Kew.


Orchids 2d ed.: The various contrivances by which orchids are fertilised by insects. By Charles Darwin. 2d edition, revised. London: John Murray. 1877.


Movement and sensitivity of flower parts; relationship to cross-fertilisation.

Letter details

Letter no.
Charles Robert Darwin
William Turner Thiselton-Dyer
Sent from
Source of text
Royal Botanic Gardens, Kew (Thiselton-Dyer, W. T., Letters from Charles Darwin 1873–81: 135–6)
Physical description
ALS 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 11605,” accessed on 30 November 2023,