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From William Trelease   26 March 1882

Madison, Wis.,

Mar. 26, 1882.

Dear Sir:

I wish to thank you for your kind and encouraging letter of Jan. 28, which was the more gratifying to me because quite unexpected.1

The origin of heterostylism is a subject that I should much like to study if I were so situated as to be able to carry out the necessary experiments. While studying Oxalis violacea I had planned a series of crossing experiments on the variable O. stricta.2 I see no reason why one with the proper facilities could not by the aid of selection and skillful crossing produce long, mid, and short styled forms in time, in a manner analogous to that in which I fancy the three forms have become fixed in nature. The difference in so minute a morphological character as the size of the pollen, and in such a physiological character as the sterility of illegitimate unions would, I suppose, be beyond the power or endurance of most men.3 If three such forms could be formed they ought to retain variability enough to allow of the production from them of forms like those of O. violacea and in a manner analogous to that in which I think the latter have been produced naturally.

Unfortunately I am moving from place to place a great deal, and it may be a long time before I settle where I can have the necessary time and facilities for such work, though if the opportunity ever comes I shall do what I can. If the forms indicated could be produced by artificial selection I think one might reasonably infer that natural selection might have worked in a similar way, though more slowly; in which case the value of crossing would be so important a factor as to explain the sterility of illegitimate unions, or any other physiological peculiarities.

I was very much interested in learning of the third form of Fritz Müller’s Pontederia.4

Once more thanking you for your kind letter, I am | Very respectfully yours, | Wm. Trelease.

1
CD’s letter has not been found, but see the letter from William Trelease, 14 January 1882 and n. 1.
2
In his study of Oxalis violacea (violet wood-sorrel), Trelease found only two stylar forms, both of which were characterised by two sets of stamens of different lengths; he concluded that the dimorphism was derived from an earlier trimorphic state (see Trelease 1882, p. 18). Oxalis stricta (yellow wood-sorrel) has both heterostylous and homostylous forms. Both species are native to North America.
3
CD referred to crosses made using pollen of the same form of flower in dimorphic or trimorphic plant species as illegitimate, and those fertilised by pollen of a different form as legitimate (see ‘Three forms of Lythrum salicaria’, p. 186).
4
Trelease had compared the case of Oxalis violacea with that of a species of Pontederia (pickerel-weed) described by Fritz Müller (F. Müller 1871). Müller had at first found only two forms but had recently discovered a third; he described it in a now missing letter to CD of 2 December 1881 (see letter to Fritz Müller, 4 January 1882 and n. 4; see also F. Müller 1883).

Please cite as “DCP-LETT-13743,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-13743