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Darwin Correspondence Project

To John Denny   22 July 1872

Down, | Beckenham, Kent.

July 22 1872

My dear Sir

I thank you for yr kind & interesting letter, which has not been too long for me by a single word.1 In my opinion the peltatum case, after you have made some more experiments, wd be worth communicating by itself to the Linn. Soc. But I also strongly think that the other cases wd be well worth giving, with a statement that the parentage of the supposed vars. was not known. You cd state that you cd perceive no marked difference between the 2 sets of vars. which are mutually sterile; & it wd add greatly to the value of yr paper, if you cd get some botanist, whose name is known, to compare the vars & to say whether he cd detect any difference which appeared of specific value.2 Please to remark how strange a fact it is that forms, to all appearance mere vars, shd be mutually sterile, whilst other vars are mutually fertile.

I dare say not one of yr experiments has been vitiated by insects not having been excluded; but you might like to hear that the pollen of a pre-potent form will fertilize a stigma, already thickly coated with its own pollen: I know this experimentally, & in the case of Primula the second dose of pollen was put on after an interval of 24 hours—3 After a grain of pollen has remained on the stigma for about half a day, & all the contents have passed down the pollen-tube, I have found the detection of the shrunken envelope of the grain very difficult.

With my best hopes for the success of yr future observations believe me my dear Sir | yours very faithfully | Ch. Darwin

P.S. I was quite delighted to see the action of the Hort. Socy. about Dr Hooker.—4


There is no evidence that Denny sent a communication to the Linnean Society concerning what he took to be inter-species crosses between the ivy-leaved pelargonium, Peltatum elegans, and zonal pelargoniums. For Denny’s other cases, see the letter from John Denny, 20 July 1872 and n. 8.
See ‘Three forms of Lythrum salicaria’, p. 187 (Collected papers 2: 121).


Discusses the mutual sterility of some varieties of Pelargonium.

Letter details

Letter no.
Charles Robert Darwin
John Denny
Sent from
Source of text
Special Collections, Library, University of Otago (DeB MS 55)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 8423,” accessed on 21 May 2018,

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