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To John Denny   9 July 1872

Down, | Beckenham, Kent.

July 9. 1872

Dear Sir

I have read with great interest yr two articles at the Congress, published in the Gardener’s Chron., copies of which I owe to the kindness of some one with the initial “D”, perhaps to you.1 I have thought that you wd perhaps excuse my asking you a question. Is the D. of Cornwall Pelargonium fertile with its own pollen, as well as with that of the 2 or 3 vars mentioned by you, whilst it is sterile with other reputed vars? Or is the Duke sterile with its own pollen & fertile only with certain vars? This latter fact is highly remarkable & wd deserve to be published in full detail—i.e. the number of trials on father’s & mother’s side &c. But the former case wd be quite new, & in my opinion of the highest importance. Might I also ask whether you have repeatedly tried to fertilize other vars of the Ivy-leaved Pelarg., besides Peltatum-elegans, with pollen of the Zonal, & have always failed; whilst, as I understand, you have succeeded easily with var. peltatum.2 Very few such cases have been recorded, & here again I hope to see full details hereafter published.3

Your statement that the transmittance of characters from either parent depends in large part on strength of constitution is quite new to me;4 & it wd be very interesting to discover whether the same rule holds with other families of plants. With respect to transmittance of character, when both parents are of equally good constitution, I shd expect from what little I know that different rules wd hold in difft families.5 If you are not already acquainted with Gärtner’s 2 works, you wd find them valuable & interesting.6

I hope that you will forgive the liberty I have taken in troubling you, & I remain with much respect | Dear Sir | yours faithfully | Charles Darwin

LS(A)

1
The Gardeners’ Chronicle, 29 June 1872, pp. 871–2, and 6 July 1872, pp. 904–10, published a report on the Birmingham Horticultural Congress; in the report, Denny’s paper ‘The relative influence of parentage in flowering plants’ was printed in two parts (Denny 1872a). The copies CD received have not been found in the Darwin Archive–CUL.
2
Denny had artificially fertilised pelargoniums in order to obtain evidence of the relative influence of the male (or pollen) parent and the female (or seed) parent on the resulting progeny (Denny 1872a). His purpose was to help horticulturists produce new cultivars by throwing light on whether the parental influence was the same when crossing varieties as when crossing species, despite the difficulty of distinguishing between species and varieties among the large number of pelargonium cultivars. Denny concluded that his experiments on crossing pelargoniums showed that the male parent had most influence on the progeny when the two parents were constitutionally equally strong. The experiments also revealed inexplicable ‘antipathies and affinities’ (p. 904); antipathies were exemplified by apparent varieties, including ‘Duke of Cornwall’, ‘Dr Muret’, and all the doubles that sprang from ‘Beauté de Suresnes’, which were fertile only with one another but not with other varieties, and affinities by the crossing of supposed distinct species as when the pollen of a zonal pelargonium fertilised a variety of ivy-leaved pelargonium Denny referred to as Peltatum elegans. Peltatum elegans was a nursery-bred plant, whose origin is now obscure, first put out in 1865 (Wilkinson 2007, pp. 166–7); horticulturists’ use of binomial nomenclature often signified a garden variety, rather than the botanical convention of genus and species.
3
In Denny 1872a, p. 904, Denny had stated: ‘My notes would furnish innumerable examples in support of the theories I have founded upon them, did time admit of my going further into detail.’
4
See Denny 1872a, p. 872. See also n. 2, above.
5
CD probably refers to the cross-breeding experiments described in Variation 1: 305–411.
6
CD’s heavily annotated copies of Gärtner 1844 and Gärtner 1849 are in the Darwin Library–CUL (see Marginalia 1: 248–98). Instances of sterility, especially between varieties, were of great importance to CD because he believed that they provided the clearest evidence of evolutionary gradation from varieties to species. For the significance he placed on Karl Friedrich von Gärtner’s experiments on crossing Verbascum, see Correspondence vol. 9, letter to J. D. Hooker, 28 September [1861] and nn. 11 and 12.

Manuscript Alterations and Comments

1.1 read] in CD’s hand above del ‘great’

Please cite as “DCP-LETT-8403,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-8403