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Darwin Correspondence Project

From Hermann Müller   25 January 1877


Jan 25. 77.

My dear Sir,

I am glad of being reminded by you of a considerable error of my book “Die Befruchtung”.1

When trying on Hottonia, I was not aware of the necessity of calculating the whole-average-numbers of seeds contained in a capsule from the average-numbers on the single plants in observation; but I was of opinion that I must not consider the fertility of the long-styled flowers legitimately fertilised, as greater than the fertility of the long-styled flowers illegitimately fertilised, unless every single long-styled plant legitimately fertilised yielded a greater average-number of seeds than every single long-styled plant illegitimately fertilised. Hence, the first of the former yielding a greater average-number than the first of the latter, the other of the former, on the contrary, yielding a smaller (although but little smaller) number than the other of the latter, I thought that any remarkable difference of their fertility was not proved by my observations.

The figures p. 351 are quite right, but the conclusion of “eben so hohe Fruchtbarkeit” p. 352 is to be corrected, and I will be very much obliged to you if you will be good enough and correct it in your review on the observations on heterostyled plants.2

Nothwithstanding this error, it is striking that the difference of fertility between legitimately and illegitimately fertilised plants is much smaller in the long-styled than in the short-styled form; and, as far as the small number of my observations permits any generalisation, the conclusion which I have drawn from the supposed equal fertility of legitimately and illegitimately fertilised long-styled plants of Hottonia, will, I think, be appliable to their, in comparison with the short-styled form, less differing fertility.

I have to return to you my hearty thanks for your kindly sending to me the second edition of your Work on Orchids, which always will remain the standard-work for every one who will explain structures of flowers.3 If any success has rewarded Hildebrand’s, Delpino’s etc., my brothers and my own attempts in this department of research, it is essentialy owing to the incitation and to the splendid model given to us by your work on Orchids.4 It has been with great delight that I have reviewed the many new observations made since the first edition.5

Believe me | Yours very sincerely | H. Müller.

CD annotations

5.1 I have … edition. 5.7] crossed pencil

Verso of last page: ‘I think I must say something about his view— | supported by Lythrum, but contradicted by *short-sty [interl] Primula, in above the short-styled form is most likely to receive own pollen is the more sterile—whilst in Pulmonaria the long-styled is the most likely to receive it is the more sterile & with Linum grandiflorum the long-styled always receives own pollen & is absolutely barren.—6 | Would it be worth while to give Table of relative [interl] fertility of the [illeg del] illegitimate union of each dimorphic species.— taking fert of short-styled as 100— that of Linum wd be 0— that of Hottonia wd be 180?7 | (Read letter)’ pencil


The letter from CD concerning Müller’s error in Die Befruchtung der Blumen durch Insekten (Fertilisation of flowers through insect agency; H. Müller 1873) has not been found; CD evidently pointed out a flaw in Müller’s experimental method (see n. 2, below).
CD had referred to the crosses of plants of the same form as ‘homomorphic’ unions and later as ‘illegitimate’ (see ‘Dimorphic condition in Primula, p. 87 (Collected papers 2: 55), and ‘Three forms of Lythrum salicaria, p. 187 (Collected papers 2: 121)). In his description of experiments with Hottonia palustris (water violet), Müller had concluded, ‘illegitime Kreuzung zwischen verschiedenen Stöcken der langgrifflegen Form bei Hottonia eben so hohe Fruchtbarkeit ergibt als legitime Kreuzungen’ (an illegitimate cross between different plants of the long-styled form in Hottonia results in just as great fertility as legitimate crosses; H. Müller 1873, p. 352). CD double-scored the passage in his copy. In Forms of flowers, p. 52, CD used Müller’s data on Hottonia, but followed his own practice of deriving mean numbers of seeds and included a table showing that the proportion of seeds legitimately produced to those illegitimately produced was as 100 to 85. In the English translation of Müller’s book (H. Müller 1883, p. 388), Müller added a footnote to his statement, noting the correctness of CD’s approach and giving the proportion of seed from the two types as CD had done.
Müller’s name is on CD’s presentation list for Orchids 2d ed. (Appendix IV).
Friedrich Hildebrand, Federico Delpino, and Fritz Müller had written many works on aspects of floral morphology that promoted cross-fertilisation; all had acknowledged CD’s pioneering role (see, for example, Hildebrand 1867, pp. 4–5, Delpino 1867, p. 4, and Fritz Müller 1868).
CD had added many further observations based on information received from Fritz and Hermann Müller, Hildebrand, and Delpino among others. CD listed relevant works published since the first edition in Orchids 2d ed., pp. vii–x.
In Forms of flowers, pp. 263–8, CD discussed Müller’s suggestion (H. Müller 1873, p. 352) that homostyled plants might have been rendered heterostyled from the effects of habit (Müller observed flies frequently carrying pollen from the long-styled form of Hottonia to the stigma of the same form), since some illegitimate unions were highly fertile, as in the case of long-styled Hottonia. CD concluded that differences in the degree of sterility of illegitimate unions in various species were incidental, following from changes gradually effected in their reproductive systems, in order that the sexual elements of the distinct forms should act perfectly on one another.
In Forms of flowers, pp. 188–243, CD did provide tables showing the fertility of illegitimate offspring of heterostyled plants.


Collected papers: The collected papers of Charles Darwin. Edited by Paul H. Barrett. 2 vols. Chicago and London: University of Chicago Press. 1977.

‘Dimorphic condition in Primula’: On the two forms, or dimorphic condition, in the species of Primula, and on their remarkable sexual relations. By Charles Darwin. [Read 21 November 1861.] Journal of the Proceedings of the Linnean Society (Botany) 6 (1862): 77–96. [Collected papers 2: 45–63.]

Forms of flowers: The different forms of flowers on plants of the same species. By Charles Darwin. London: John Murray. 1877.

Müller, Hermann. 1873. Die Befruchtung der Blumen durch Insekten und die gegenseitigen Anpassungen beider. Ein Beitrag zur Erkenntniss des ursächlichen Zusammenhanges in der organischen Natur. Leipzig: Wilhelm Engelmann.

Müller, Hermann. 1883a. The fertilisation of flowers. Translated and edited by D’Arcy W. Thompson. London: Macmillan and Co.

Orchids 2d ed.: The various contrivances by which orchids are fertilised by insects. By Charles Darwin. 2d edition, revised. London: John Murray. 1877.

‘Three forms of Lythrum salicaria’: On the sexual relations of the three forms of Lythrum salicaria. By Charles Darwin. [Read 16 June 1864.] Journal of the Linnean Society (Botany) 8 (1865): 169–96. [Collected papers 2: 106–31.]


Thanks CD for calling attention to a "considerable error" in his observations on Hottonia fertility [in Die Befruchtung der Blumen (1873)]. [See Forms of flowers, p. 52.]

Letter details

Letter no.
Heinrich Ludwig Hermann (Hermann) Müller
Charles Robert Darwin
Sent from
Source of text
DAR 110: A26–7
Physical description
ALS 3pp ††

Please cite as

Darwin Correspondence Project, “Letter no. 10815,” accessed on 13 July 2024,