To M. J. Berkeley   7 April [1855]

Down Farnborough Kent

April 7th

My dear Sir

I hope that you will forgive my troubling you & begging a great favour.— I saw the other day at Kew your very curious specimen of Peas affected by pollen,1 as described by Wiegmann2 & Gærtner.—3 I am going to plant in 2 or 3 days a bed with 41 reputed varieties of Peas to see how far they really differ (& of course I shall observe whether any of the Peas are affected by chance hybridisation)4 & I want very much a dozen of the curious brown Peas, or Pois sans Parchemin. I have sent to London for this var. but have today received a white smallish Pea, called the Sugar Pea. Now I write to know whether you happen to have a few of the brown peas, & could spare me a dozen to plant, & if you can whether you wd. be so kind as to send me them per Post.—

I have been reading straight through Gærtner which for me, a very poor German scholar has been a gigantic task.5 As I know from your excellent abstract that you have read it carefully,6 I shd. very much like to know (& my notes from your Abstract are hardly copious enough for me to tell) whether you were at all puzzled by any expressions on the fertility of Hybrids: he is never weary of stating that hybrids, though fertile, invariably produce a less number of seeds than the pure parents; yet every now & then there occur expressions which make me suspect that the author has misgivings on this head: moreover he always ranks lessened fertility as a less important character in Hybrids than variability &c &c.— It has struck me that it wd. be not a little difficult to ascertain the normal number of seeds in so many pure species, & with a strong impression on the less fertility of Hybrids, a person might easily deceive himself.— In the table7 the surprising number of times, he gives, (i a), as the degree of fertility, so very close to (K), & yet the fewness of times, he gives actually (K), (& nevertheless shows how beautifully graduated the sterility in all the lower degrees is) strikes me as rather odd.—8

Lastly I cannot understand how it is, that he does give (K) or normal fertility in some few cases in the Table (as in Lobelia cardanalifulgens & reverse; Lychnis diurna & vespertina; malva mauritiano-sylvestris; Verbascum Lychnitis albo-pyramidatum), yet in the text seems to disregard these examples;—at least he often repeats (as at p. 102) that fertility in hybrids never equals that of the pure species.

If this point occurred to you, & if (as is very probable) the subject has not gone out of your mind, I shd. be extremely glad to hear what you think. Though in truth I have much cause to apologise for writing at such length; & though it is but a poor excuse, I assure you I had no intention whatever of asking your opinion on this head when I began to write.

Pray believe me | My dear Sir | Yours very sincerely | Charles Darwin

Did any of your Peas cross each other without artificial aid? Wiegmann’s & some of Gærtner’s Peas having crossed of themselves seems to me an extraordinary part of this extraordinary case.9

Have you ever corresponded with Gærtner, & do you know his address?10 If I can get no light from you, or from relooking over whole book, I shd very much like to venture to write, & ask him on the above point, & indeed on two or three others.—11 What an admirable Book it appears: but did you observe what endless errors in the References.—

1
CD believed he had seen the peas described by Berkeley in Gardeners’ Chronicle and Agricultural Gazette, no. 25, 24 June 1854, p. 404, and also mentioned biefly in Berkeley 1850–1 (see n. 6, below). These peas were a different colour from the normal peas of the mother plant, an effect that Berkeley ascribed to the direct action of the pollen of the other parent on the outer coating of the ovule. However, CD had been misled by inaccurate labelling at Kew (see letter to J. D. Hooker, 13 April [1855]).
2
Wiegmann 1828. A copy is in the Darwin Library–Down. CD recorded having read the work early in 1844 (Correspondence vol. 4, Appendix IV, 119: 13a), but he may have reread it in conjunction with his study of Gärtner 1849. Wiegmann 1828 is also mentioned in Berkeley 1850–1.
3
Gärtner 1849, pp. 497–9. CD’s copy of Gärtner 1849, in the Darwin Library–CUL, is heavily annotated. On the cover is written: ‘When read Make Abstract; & read over abstract of Koelreuter & make [interl] abstract of Herbert. & look over Portfolio | When finished read Berkeley Criticisms on..’ On the title-page, CD wrote: ‘I think began Sept 15th/54’. Stuck to the back cover is a note dated October 1855 that reads, in part: ‘This work is abstracted & abstract distributed, except the Bundle herein enclosed. *The abstract has been carefully compared with those of all Köelreuter & Herbert &c &c &c [added pencil]’. The abstracts of Gärtner 1849, Kölreuter 1761–6, and Herbert 1837 are in a substantial memorandum book (DAR 116).
4
CD had several projects in mind, one of which was to ascertain whether varieties of pea plants kept their distinguishing features when grown in conditions that allowed free crossing between the plants. In his Questions & experiments notebook, p. 8 (Notebooks), he wrote: ‘In the nurseries, when *seed of [interl] the varieties of Cabbages, peas, beans, as raised, do the Seedsmen select at all from the plants? If not, I am surprised [’plan‘ del] such plants do not degenerate,—as the Bees will mingle the infinitesimal varieties which must occur.— [reverse question mark] is it [interl] not these infinitesimal varieties, which counterbalance each other?’ See also letter to William & Julius Fairbeard, [October 1855 – May 1856]. Arend Friedrich August Wiegmann had made the point in Wiegmann 1828, pp. 14, 26, and 34–5, that the peas to be used for crossing experiments needed to be planted far away from other peas (noted by CD in his Questions & experiments notebook, p. 13v. (Notebooks)). Similarly, Wiegmann claimed that peas hybridised readily with other genera, a point which Karl Friedrich von Gärtner seemed to confirm (see Natural selection, pp. 69–71). A copy of John Cattell’s seed catalogue for 1855, extensively marked by CD, is in DAR 46.2: 1, and the tabulations of the results of CD’s experiments on peas and other vegetables are in DAR 46.2: 3–31, 37–41.
5
CD recorded that he reread Gärtner 1849 in June 1855 (DAR 116 (ser. 5): 1), although his abstract of the work was only completed in October (see n. 3, above).
6
Berkeley 1850–1, a review of Gärtner 1849. CD’s annotated copy of the first section of the review is in the Darwin Library–CUL.
7
Gärtner 1849, pp. 684–728. On p. 684, CD wrote in pencil: ‘(Get Hooker to read over this list)’. Another note, also in pencil, reads: ‘There are important facts [‘not’ del] in this Table not noticed in my abstract on results.’
8
CD had carefully studied Gärtner’s table of hybrid crosses between plants (Gärtner 1849, pp. 684–728). He extracted certain figures from the table and discussed them in detail, paying particular attention to the way in which Gärtner had categorised degrees of fertility in the offspring (DAR 116 (ser. 2): 1–9 and (ser. 3): a–f). Gärtner listed ten categories ranging from complete infertility (a) to complete fertility (k). As CD noted in the letter, Gärtner only rarely gave a ‘k’ rating to hybrids.
9
It was ‘extraordinary’ to CD because he believed that papilionaceous plants such as peas, beans, and clover were difficult to cross. See Questions & experiments notebook, pp. 7, 15 (Notebooks), in which he expressed his idea that the structure of the flower impeded cross-fertilisation. CD described his opinion in Natural selection, pp. 68, 71.
10
Gärtner had died in 1850.
11
In an undated, unbound slip associated with CD’s notes on Gärtner 1849 (DAR 116), CD made a ‘List of cases in which Gærtner affixes (K)’. To this he added in pencil: ‘Ask Author Look in Index to see whether he considers any of them vars.’

Manuscript Alterations and Comments

1.3 described by] ‘by’ over ‘in’
2.9 in Hybrids] interl
2.11 so many] above del ‘the’
2.13 yet] interl
2.15 all the] interl
2.15 is)] parenthesis over comma
3.1 fertility] ‘fe’ over illeg
3.2 reverse;] semicolon over colon
3.5 (as at p. 102)] interl
4.1 (as] parenthesis over comma
6.2 some of] interl
7.4 endless] after del ‘an’

Please cite as “DCP-LETT-1662,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-1662