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Darwin Correspondence Project

From W. T. Thiselton-Dyer   31 May 1874

10 Gloucester Road, Kew

May 31. 1874

My dear Mr Darwin

Some time ago you asked me to try the effect of syringing plants with sensitive flowers.1 Opuntia is one of these and as there are a good many in flower in the Cactus house I got Mr Smith the Curator to go with me this morning and experiment upon them.2 In its so to speak virgin state the flower has the stamens spread out with a greater or less divergence from the style—


They do not use syringes with a nose at Kew but produce a spray by placing a finger over the nozzle. Mr Smith who is an adept at this and who was much interested in trying the flowers, syringed them successively.

I confess I was astonished at the readines with which the lightest syringing we could give them elicited movement. The contraction was not instantaneous but there was always a perceptible interval of time—not more than a second or so perhaps—and then the stamens gradually moved towards the style.


We tried two species in particular O. polyacantha and O. monacantha3

You asked me about Stapelias—4 I cannot find anything about movement in their flowers. I should expect the parts to be quite stationary. Probably there is some provision for cross fertilization by the removal of the pollen masses which is not yet worked out. Asclepiadaceæ are a kind of analogue amongst Dicotyledons of Orchideæ amongst Monocotyledons.5

Prof. Oliver6 called my ⁠⟨⁠a⁠⟩⁠ttention the other day to the way in which plants capture insects sometimes by means of their flowers. He had an idea that the nectar poisoned them, mentioning the Oleander as one case in point.7 Ledum palustre,8 a specimen of which I inclose, he thought was another instance. Here however it seems to me that the insects are caught by the viscidity of the ovary and according to Weale, Linn. Journ. xiii pp. 48, 49 Gomphocarpus physocarpus capture⁠⟨⁠d⁠⟩⁠ insects which “got attached to the stigmatic glands and appeared unable to release themselves”9   Of course in this way the soil above the plant would get enriched with nitrogenous matters. But I suppose that the destruction of the insects is merely an accidental concomitant of the glutinousness which is brought about in connection with some other purpose

Meehan appears to have noticed the closing of the expanded lobes of the stigma in many Scrophulariaceæ and Bignoniaceæ—. He has lately observed it in Catalpa.10 If I can keep it in my recollection when Catalpa comes into flower I will try the effects of syringing

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

CD annotations

4.1 I cannot … themselves” 5.8] crossed pencil


Opuntia is the genus of paddle cacti. Thiselton-Dyer refers to John Smith (1821–88).
Opuntia polyacantha is the hairspine cactus or panhandle prickly pear; O. monacantha is the drooping prickly pear or Barbary fig.
See letter to W. H. Thiselton-Dyer, 4 April 1874 and n. 6.
Asclepiadaceae is now subsumed within the family Apocynaceae (milkweed). Orchideae is the largest tribe in the orchid subfamily, Orchidoideae. In milkweed and orchids the pollen is grouped into complex structures called pollinia. Dicotyledons have seeds with two embryonic leaves, and monocotyledons have one.
Nerium oleander has poisonous flowers.
Ledum palustre (now Rhododendron tomentosum) is marsh Labrador tea.
Gomphocarpus physocarpus (or Asclepias physocarpa, the balloonplant or swan plant) is described in James Philip Mansel Weale’s paper on fertilisation in the Asclepiadeae, published in the Journal of the Linnean Society (Weale 1870).
Thomas Meehan’s observations on Scrophulariaceae and Bignoniaceae were reported in the Proceedings of the Academy of Natural Sciences of Philadelphia 25 (1873): 277. Catalpa is a genus of spreading deciduous trees in the Bignoniaceae family, including C. bignonioides (Indian bean tree).


Movement in plants; effect of syringing on Opuntia plants that capture insects with their flowers.

Letter details

Letter no.
William Turner Thiselton-Dyer
Charles Robert Darwin
Sent from
London, Gloucester Rd, Kew, 10
Source of text
DAR 178: 93
Physical description
ALS 7pp †

Please cite as

Darwin Correspondence Project, “Letter no. 9478,” accessed on 3 February 2023,

Also published in The Correspondence of Charles Darwin, vol. 22