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Darwin Correspondence Project

To Robert Caspary   21 February [1866]1

Dear Sir

I hope you will excuse the liberty which I take in begging a favour of you. You read a paper at the Amsterdam Hort: Congress on cases like that of Cytisus Adami. Would you have the kindness to tell me where this has been, or will be, published? and if you have a spare copy I should be grateful for it.2 If you do not intend to publish it I beg you not to take the trouble to answer this note as I shall understand your silence.

I am very much interested in this subject which I hope you will receive as some excuse for my troubling you.3

With very sincere respect I beg leave to remain | Dear Sir | yours faithfully | Ch. Darwin

Down Bromley, Kent | Feb. 21st.


The year is established by the relationship between this letter and the letter from Robert Caspary, 25 February 1866.
Caspary delivered the paper on Cytisus adami (now +Laburnocytisus adamii) and other hybrids that he believed were produced by grafting at the International Congress of Botany and Horticulture held at Amsterdam from 7 to 12 April 1865 (Caspary 1865a). CD had read a notice of the paper in the Gardeners’ Chronicle, 29 April 1865, p. 386 (see Correspondence vol. 13, letter to J. D. Hooker, [1 May 1865], and letter from M. T. Masters, 12 July 1865). The paper appeared in Bulletin du Congrès International de Botanique et d’Horticulture réuni à Amsterdam (1865): 65–80; CD’s offprint of the paper, bound with an annotated handwritten English translation, is in the Darwin Pamphlet Collection–CUL.
CD had long been interested in Cytisus adami (now +Laburnocytisus adamii), a hybrid produced by grafting a scion of Cytisus purpureus (a synonym of Chamaecytisus purpureus, purple broom) onto a stock of Laburnum anagyroides (the common yellow laburnum). See Correspondence vols. 4–6, 10, and 11. Unlike most grafts, which preserve the floral character of the scion, +L. adamii has branches of purplish-yellow flowers, which regularly revert to those of both parent species (Bean 1970–88, 2: 510–11). CD had tried to propagate the hybrid by seed, and to produce the hybrid by crossing, but without success (see Correspondence vol. 6, letter to J. D. Hooker, 8 September [1856], and Correspondence vol. 10, letter to Daniel Oliver, 24 July [1862]). CD discussed the plant in Variation 1: 387–97, 405–11, and 2: 37, 364–5, noting the ‘extraordinary fact’ that two distinct species could ‘unite by their cellular tissue, and subsequently produce a plant bearing leaves and sterile flowers intermediate in character between the scion and stock, and producing buds liable to reversion; in short, resembling in every important respect a hybrid formed in the ordinary way by seminal reproduction’ (Variation 1: 390). He argued that the plant was a graft-hybrid, and not a product of sexual union, citing Caspary 1865a and other information obtained from Caspary’s letters (Variation 1: 388–9). Because it displayed both fusion and reversion of characters, +L. adamii served to illustrate the similarity of asexual and sexual modes of reproduction, an important aspect of CD’s theory of pangenesis (see Variation 1: 411, 2: 364–5, and Olby 1985, pp. 76–80).


Bean, William Jackson. 1970–88. Trees and shrubs hardy in the British Isles. 8th edition, fully revised by D. L. Clarke and George Taylor. 4 vols. and supplement. London: John Murray.

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Olby, Robert. 1985. Origins of Mendelism. 2d edition. Chicago and London: University of Chicago Press.

Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.


Requests copy of paper read at Amsterdam Horticultural Congress, on graft-hybrids like that of Cytisus adami [see 5018].

Letter details

Letter no.
Charles Robert Darwin
Johann Xaver Robert (Robert) Caspary
Sent from
Source of text
Yale University: Beinecke Rare Book and Manuscript Library (GEN MSS MISC Group 1559 F-2)
Physical description
LS(A) 3pp

Please cite as

Darwin Correspondence Project, “Letter no. 5012,” accessed on 3 June 2023,

Also published in The Correspondence of Charles Darwin, vol. 14