To W. T. Thiselton-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

1
The year is established by the relationship between this letter and the letter from W. T. Thiselton-Dyer, 16 July 1878.
2
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.
3
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.
4
Thalia species are native to the Americas and Africa; no other species of the genus was recorded as being sent from Kew.

Manuscript Alterations and Comments

1.2 & I … week:] interl
1.3 that of] interl
2.1 motile] above del ‘sensitive,’
2.1 (so … up.) 2.2] interl
2.4 the] after del ‘wh’
2.4 under] after del ‘wh’
3.1 I] after del ‘This’
3.2 besides T. dealbata] interl

Please cite as “DCP-LETT-11605,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-11605