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Darwin Correspondence Project

From John Denny   12 July 1872

Stoke Newington

July 12th. 1872

Dear Sir

Thinking you might be interested in the subject I endeavoured to treat of I took the liberty of forwarding you my paper.1

In reply to your queries, the Duke of Cornwall Pelargonium is fertile with its own pollen.

With regard to the Ivy leaved sections, I have repeatedly tried to fertilize other varieties besides Peltatum Elegans, but have invariably failed to do so.2

Others besides myself have (of late) obtained hybrids from Peltatum Elegans, but have also failed to do so from other varieties

Mr. Grieve has succeeded in obtaining a golden variegation in the foliage of Peltatum Elegans, by employing the pollen of a gold & bronze bi-color.3

To ascertain whether the transmittance of character, under certain conditions, differs in different families of plants, requires the accumulation of data my paper advocates; and for this object, as well as for the discussion of the subject, of the influence of parentage, in all its branches, and bearings, I should like to see a really working society formed.

I have not seen Gärtners works, & I fear they are in German.4

My experiments upon the Pelargoniums have been conducted with more than ordinary care, & that you may be able to judge of this fact, I take the further liberty of forwarding you a number or two of “The Florist”, which contain a detailed account of my mode of procedure.5

I am just now endeavouring to fertilize Peltatum Elegans with the pollen of the wild blue geranium, & there are signs of my having succeeded but which I fear are but delusive; to succeed in such a cross would be most interesting6

From Chiswick I have received a communication informing me, that in a number of seedling grapes raised—from careful cross-fertilization, my theory of the pre-potence of the male parent—is fully borne out.7

I have also received other interesting communications upon the subject of my paper.8

In Orchids I think you have carried out a series of experiments,—& therefore could give us some valuable information.9

I shall continue my experiments on the Pelargonium—& if time, upon other flowers, & should be happy with your permission to inform you of any results that appear to me worthy of special notice.

Thanking you for your note, | Believe me to remain | Dear Sir | Yours faithfully | John Denny

P.S. There is no need to return the numbers of the Florist


See letter to John Denny, 9 July 1872 and n. 2. The extensive cross-breeding of pelargoniums by florists and nurserymen, especially in the early nineteenth century, and the consequent problem of distinguishing hybrids from species and varieties, made pelargonium classification (and the subsequent identification of old cultivars) difficult. Both botanists and horticulturists began to group pelargoniums into named sections in order to make recognition easier, but the two classificatory systems differed in their method of ordering. From 1860, William Harvey’s division of the genus into fifteen sections became the accepted standard for botanists. Horticulturists, however, continued to base their sections on appearance and use, regardless of whether a plant was a species or a hybrid, with some plants appearing in more than one section. What horticulturists termed the ivy-leaved section was not popular among breeders until the production of some attractive hybrids in the early 1870s. See Wilkinson 2007, pp. 8–11, 70–1, 160–7, 251–66, and D. Miller 1996, pp. 25–9.
Denny may refer to Peter Grieve’s new strain produced by fertilising a variety of an ivy-leaved pelargonium with the pollen of a zonal; this was reported on in Gardeners’ Chronicle, 8 June 1872, p. 762. CD had asked about such crosses in his letter to Denny of 9 July 1872. ‘Bicolor’ usually refers to pelargoniums with two colours in the upper petals of the flower, but Denny appears to use it to denote the colouring of the foliage. Zonal pelargoniums are so called because their leaves are divided into two colour zones. Pelargonium peltatum and Pelargonium zonale (from which all zonal pelargoniums derive) belong to the same botanical section Ciconium (see D. Miller 1996, p. 160). Denny specialised in breeding zonal pelargoniums (Wilkinson 2007, p. 177).
CD had recommended that Denny read Gärtner 1844 and Gärtner 1849 (see letter to John Denny, 9 July 1872 and n. 6).
Denny’s article ‘On cross-breeding pelargoniums’ was published in three parts in the Florist (Denny 1872b). CD’s annotated copies are in the Darwin Pamphlet Collection–CUL.
The wild blue geranium, Geranium pratense, is commonly known as the meadow cranesbill. Pelargoniums were originally thought to belong to the same genus as geraniums, but in 1792 the botanist Charles L’Héritier separated them into two distinct genera of the family Geraniaceae. Geraniums are native to Europe; pelargoniums, native to South Africa, were not introduced into Europe until the seventeenth century. (W. J. Webb 1984, pp. 7–9.) It is possible that Denny was attempting to produce a blue-flowered pelargonium (Wilkinson 2007, p. 178).
For Denny’s theory of the prepotence of the male (or pollen) parent, see Denny 1872b, p. 50, and the letter to John Denny, 9 July 1872 and n. 2. The communication from Chiswick may have come from Archibald Barron, superintendent of the Royal Horticultural Society’s garden at Chiswick, or from William Turner Thiselton-Dyer, recently appointed professor at the Royal Horticultural Society. Barron had special charge of the vines at Chiswick. See Fletcher 1969, pp. 215–20.
These communications might have included information from the editors of the Journal of the Royal Horticultural Society, Miles Joseph Berkeley and Thiselton-Dyer, about the relative size of pollen-grains in different varieties affecting whether fertilisation occurs or not. The editors may have communicated with Denny before publishing this information at the end of the version of Denny 1872a that was reprinted in their journal (Denny 1872d, p. 24).
CD’s experiments aimed to show that the floral morphology of most orchids prevented self-fertilisation (see Orchids, especially pp. 249–65). CD had therefore studied prepotency of pollen from a separate individual within the same species, or even from a separate flower on the same plant, but had not looked at hybrids from the perspective that interested Denny, namely which parent’s characteristics dominated the hybrid.


Fletcher, Harold R. 1969. The story of the Royal Horticultural Society 1804–1968. London: Oxford University Press for the Royal Horticultural Society.

Gärtner, Karl Friedrich von. 1844. Versuche und Beobachtungen über die Befruchtungsorgane der vollkommeneren Gewächse und über die natürliche und künstliche Befruchtung durch den eigenen Pollen. Pt 1 of Beiträge zur Kenntniss der Befruchtung der vollkommeneren Gewächse. Stuttgart: E. Schweizerbart.

Gärtner, Karl Friedrich von. 1849. Versuche und Beobachtungen über die Bastarderzeugung im Pflanzenreich. Mit Hinweisung auf die ähnlichen Erscheinungen im Thierreiche, ganz umgearbeitete und sehr vermehrte Ausgabe der von der Königlich holländischen Akademie der Wissenschaften. Stuttgart: E. Schweizerbart.

Miller, Diana. 1996. Pelargoniums: a gardener’s guide to the species and their cultivars and hybrids. London: B. T. Batsford.

Orchids: On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing. By Charles Darwin. London: John Murray. 1862.

Webb, William J. 1984. The Pelargonium family: the species Pelargonium, Monsonia, and Sarcocaulon. London and Dover, N.H.: Croom Helm.

Wilkinson, Anne. 2007. The passion for pelargoniums: how they found their place in the garden. Stroud: Sutton Publishing.


Replies to CD’s queries. Duke of Cornwall Pelargonium is fertile with its own pollen. Has failed to produce hybrids from other varieties besides P. peltatum and P. elegans. Sends numbers of the Florist which contain an account of his mode of procedure ["On cross-breeding pelargoniums" Florist & Pomologist (1872): 10, 34, 50].

Reports a confirmation of his theory of the prepotence of the male parent.

Letter details

Letter no.
John Denny
Charles Robert Darwin
Sent from
Stoke Newington
Source of text
DAR 162: 159
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 8407,” accessed on 30 March 2020,

Also published in The Correspondence of Charles Darwin, vol. 20