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Darwin Correspondence Project

From Asa Gray   [27 and 29 August] and 2 September [1861]1

to carry down the pollinia, taken from one flower on the point of a fine needle, to the stigma of another flower, have failed,—the pollinia lodging above the stigma or over on the dorsal face.2 I enclose a spike of S. cernua.

Sept. 2d. That Drosera filiformis should show no sensitiveness is perhaps not remarkable, for it is not well arranged for fly-catching.3 But I have got some D. rotundifolia, & tried it with atoms of fresh fish laid on the viscid tips, but I could detect no movement either immediate or later. Yet I could see that some of the leaves had their bristles turned inwards and had been catching flies. I have been to-day into the country and have brought in some fres⁠⟨⁠h⁠⟩⁠ D. rotundifolia, to try again to-morrow.

The most marked diœcio-dimorphous flowers I know are in Rubiaceæ, and the most familiar cases are in Houstonia (Oldenlandia, but the old name & genus will be restored) specially our H. purpurea and the everywhere common H. cærulea, and Mitchella repens. Spermacoce virginiana & Diodia teres, also show it. I have no data for a list; but the cases are numerous. I will make any observations you will indicate next spring.4

What you say of Mill well accords with what Prof. Henry of Smithsonian Instn. says of your investigations., your method, &c,—and he is the best judge of the logic of investigation I know of.5

CD annotations

1.1 to carry … to-morrow. 2.6] crossed ink
3.2 Oldenlandia] underl red crayon
4.1 What … know of. 4.3] crossed ink


The date is established by CD’s statement in the letter to Asa Gray, 17 September [1861], that he had just received Gray’s letter ‘of Augt 27th & 29th & Sept 2d’.
CD had asked Gray, in his letter of 21 July [1861], to ‘have a look at Spiranthes’ in order to confirm his description of the orchid’s flower structure. Gray had apparently found differences in the sexual parts of American species of Spiranthes. See also letter to Asa Gray, 17 September [1861].
CD had suggested that Gray might like to observe the sensitivity of Drosera leaves to substances placed on them (see letter to Asa Gray, 17 February [1861]). The thread-leaved sundew, D. filiformis, is common in wet, sandy, coastal areas from Massachusetts southward. See also letter to Asa Gray, 21 July [1861].
CD had asked Gray whether he knew of any dimorphic plants in which the two flower forms occur on separate plants living commingled in the same area (see letter to Asa Gray, 5 June [1861]). In his Manual of the botany of the northern United States, Gray defined the term ‘diœciously dimorphous’ in the section describing the Rubiaceae, stating that in ‘several genera, such as Mitchella, Oldenlandia, &c., the flowers, although perfect, are of two sorts in different individuals’, one with ‘exserted’ (protruded) stamens and short styles and the other ‘included’ stamens and long styles (A. Gray 1856, p. 171 n.). The term had first been defined in Torrey and Gray 1838–43, 1: 38. See also letter from Asa Gray, 11 October 1861.
See the letter to Asa Gray, 21 July [1861], in which CD mentioned that John Stuart Mill considered CD’s reasoning in Origin to be ‘in the most exact accordance with the strict principles of logic.’ The physicist, Joseph Henry, was the secretary and director of the Smithsonian Institution in Washington, DC. Diodia teres is a synonym of Hexasepalum teres.


Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.


Gives some observations on the sensitivity of Drosera species and comments on cases of "dioecio-dimorphism".

Letter details

Letter no.
Asa Gray
Charles Robert Darwin
Sent from
Source of text
DAR 110 (ser. 2): 76
Physical description
inc †

Please cite as

Darwin Correspondence Project, “Letter no. 3242,” accessed on 5 February 2023,

Also published in The Correspondence of Charles Darwin, vol. 9