To Asa Gray   16 September [1861]1

Down Bromley Kent

Sept. 16th

My dear Gray

In the whirl of your public affairs, science may be forgotten, or if not forgotten you may have no inclination to write. But if so inclined I shd. be very glad to have a little information on any cases of dimorphism, like that of Primula, & to be allowed to quote you.—2 To make sure that you may understand what I want to know: I give this beautiful diagram of the two forms of Primula.

diagram

I think I have made out their good or meaning clearly. The pollen of A is fitted for stigma of B & conversely. The individuals are divided into two sets or bodies, like the males & females of Quadruped; but both in Primula are hermaphrodites: but I will not enter on details, as I will soon send a paper to Linn. Soc.y.—3 I should be eminently glad to know of other analogous cases. Are the two forms ever borne on same plant? Thyme is a different case: as the one form is simply female, stamens having aborted; these females, however, I find to be the most productive of seed.4 Some of the species of Linum offer this case:

diagram

I am rather too late to experiment fairly; but I am almost sure that pollen of A is absolutely sterile on stigma of A: but good for stigma of B: whereas pollen of B is good for its own stigma B & for stigma of A.—5

This subject interests me much, so do help me if you can; for I have some very faint hopes that it may throw some light on Hybridisation;6 I have sown seeds of Primulas raised in very scanty numbers from stigmas fertilised by what I call a homomorphous union; ie by pollen from plant of same form.—

If you have looked at Spiranthes let me hear:7 but if your Spiranthes are like S. speciosa figured by Bauer:8 they are very different from our S. autumnalis; which by the way at Torquay I had the good luck to see Bees fertilise: I have almost finished my long Orchis paper,9 & then I must go back to my true work on Cocks & Hens, fowls & rabbits.10 Eheu Eheu, what much better fun observing is than writing.

By the way I have just been amusing myself in looking at Dionæa in aid of my Drosera work. How curious it is to see a fly caught & how beautiful are the adaptations compared with Drosera. But I must not run on about my hobby Horses.

Farewell | My dear Gray | Yours very sincerely | Charles Darwin

1
The year is given by the reference to CD’s statement that he will ‘soon send a paper’ on Primula to the Linnean Society of London (see n. 3, below).
2
CD had been actively studying what he called the ‘dimorphic condition’ of Primula since the spring of 1860 (see Correspondence vol. 8). Some of his notes and experimental records on Primula and other dimorphic plants are in DAR 108 and 111.
3
CD read his paper ‘On the two forms, or dimorphic condition, in the species of Primula, and on their remarkable sexual relations’ to the Linnean Society on 21 November 1861. See Collected papers 2: 45–63.
4
CD had studied thyme plants earlier in the summer and made notes on wild thyme growing near Torquay when visiting the area in July and August 1861 (see DAR 109: 18–20 and DAR 157a, p. 72).
5
CD referred only briefly to heterostyly in two Linum species in the Primula paper, stating that he intended to carry out further hybridisation experiments on the two forms (Collected papers 2: 62–3). His paper on this topic, ‘On the existence of two forms, and on their reciprocal sexual relation, in several species of the genus Linum’, was read to the Linnean Society in February 1863 (see Collected papers 2: 93–105). In this paper, CD stated that he had put some pollen from the short-styled plants on the stigmas of long-styled plants and, although ‘it was late in the season, namely September 15th’, ultimately obtained ‘six fine capsules’, which he planted the following spring (Collected papers 2: 94).
6
Sterility and hybridisation are discussed in the conclusion of the Primula paper (Collected papers 2: 61): The simple fact of two individuals of the same undoubted species, when homomorphically united, being as sterile as are many distinct species when crossed, will surprise those who look at sterility as a special endowment to keep created species distinct. Hybridizers have shown that individual plants of the same species vary in their sexual powers, so far that one individual will unite more readily than another individual of the same species with a distinct species. Seeing that we thus have a groundwork of variability in sexual power, and seeing that sterility of a peculiar kind has been acquired by the species of Primula to favour intercrossing, those who believe in the slow modification of specific forms will naturally ask themselves whether sterility may not have been slowly acquired for a distinct object, namely, to prevent two forms, whilst being fitted for distinct lines of life, becoming blended by marriage, and thus less well adapted for their new habits of life.
7
CD had asked Gray to examine the flower structure of American species of the orchid Spiranthes. See Correspondence vol. 8, letter to Asa Gray, 31 October [1860]; see also letters to Asa Gray, 11 April [1861] and 5 June [1861].
8
Bauer 1830–8.
9
CD was intending to publish his work on orchids in the journal of the Linnean Society of London. After the manuscript was finished, however, he decided to publish it as a small book (see letter to John Murray, 21 September [1861]).
10
CD refers to the manuscript he was preparing to support his view that there was extensive variation present in domesticated plants and animals on which both artificial and natural selection could operate. Variation appeared in two volumes in 1868.

Manuscript Alterations and Comments

3.2 it may] ‘it’ after del ‘I’
4.2 our] interl

Please cite as “DCP-LETT-3255,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-3255