To J. D. Hooker   4 April [1866]1

Down—

April 4th.

My dear Hooker

We have had G. Henslow here for two days & are very much pleased with him: there is something very engaging about him.—2

Many thanks about the Bonatea & the Water-lilies & about the Cucumber case.3 Ask Mr Smith whether by any odd chance he has ever seen a bud with blended character arising from junction of stock & graft.—4

I will not forget about orchids; but it is not likely we shall have any to send you.— It was really very good in you to write about Pangenesis; for all such remarks lead one to see what points to bring out clearly.—5 I think you do not understand my notions on Pangenesis

Firstly.— I do not suppose that each cell can reproduce the whole species. The essence of my notion is that each cell, by throwing off an atom or gemmule (which grows or increases under proper conditions) reproduces the parent-cell & nothing more; but I believe that the gemmules of all the cells congregate at certain points & form ovules & buds & pollen-grains.6 I daresay they may congregate within a preexisting cell, passing through its walls like contents of pollen-tubes into embryonic sack; & it was partly on this account that I wished to learn about first appearance of buds.—7 When you speak of “a single detached cell of Begonia becoming a perfect plant”; I presume you do not mean that each cell, when separated by the knife, will grow; but that a fragment of a leaf will produce buds at apparently every & any point;8 if you mean more, I shd. be specially grateful for information.—

Secondly.— I do not suppose that gemmules are preserved in each species of all its preexisting states up to the “irrepressible monad”; but am forced to admit that wonderfully many are thus preserved & are capable of development, judging from reversion; but reversion does not go to such astounding lengths as you put it.9

Thirdly. I do not suppose that a cell contains gemmules of any future state; but only that when a cell is modified by the action of the surrounding cells or of the external conditions, that the so modified cell throws off similarly modified atoms of its contents or gemmules which reproduce the modified cell.—10

I have made a memorandum to ask you, (for I am very curious on subject,) when we meet, what R. Brown & Griffith predicted:11 I conjecture such cases would come under what I call “correlation” in the Origin.—12 I am not surprised that you think Pangenesis is only a statement of the concrete; so now it almost appears to me; yet I declare it has been nothing less than revelation to me as clearing away mist & connecting various classes of facts. The key-stone of the view is that the reproductive organs do not form the reproductive male & female elements,—only collect them (i.e. the gemmules of each separate cell) by some mysterious power in due proportions & fit them for mutual action & separate existence.—

If any remarks or sneers on this subject occur to you, for the love of Heaven, make a memorandum that I may sometime hear them.—

Ever yours affect. | C. Darwin

1
The year is established by the reference to George Henslow’s visit (see n. 2, below), and by the discussion of CD’s hypothesis of pangenesis.
2
Emma Darwin’s diary (DAR 242) records that Henslow arrived at Down on 2 April 1866.
3
No letter from Hooker containing information on these plants has been found. In Variation 1: 403, CD states that Hooker had informed him of an observation made by John Smith (1798–1888),the retired curator of the Royal Botanic Gardens, Kew, that the development of the ovary in the South African orchid Bonatea speciosa ‘could be effected by mechanical irritation of the stigma’. CD had previously studied dried specimens of B. speciosa (Orchids, p. 304 n.). For CD’s interest in the plant, see Orchids, pp. 302–5, and Correspondence vol. 13, letter from Roland Trimen, 13 December 1865, n. 1. CD was interested in waterlilies as possible exceptions to his view that it was necessary for individuals to cross at least occasionally (see letter from Robert Caspary, 25 February 1866 and n. 13). On the cucumber case, see the letter to J. D. Hooker, [5 April 1866] and n. 2.
4
CD refers either to John Smith (1798–1888), or to John Smith (1821–88), curator of the Royal Botanic Gardens, Kew. CD was interested in the effect of stock on scion tissue for its bearing on his theory of pangenesis. See letter to Robert Caspary, 21 February [1866] and n. 3.
5
The letter from Hooker on pangenesis has not been found. CD’s theory of the transmission and development of hereditary characters was published in the chapter headed ‘Provisional hypothesis of pangenesis’ in Variation 2: 357–404. He had discussed his hypothesis with Thomas Henry Huxley at the end of May 1865, enclosing a thirty-page draft of the chapter (see Correspondence vol. 13, letters to T. H. Huxley, 27 May [1865] and 30 May [1865]). For more on CD’s ideas on heredity and generation, which developed over a thirty-year period, see Kohn 1980, Hodge 1985, and Olby 1985. On CD’s hypothesis of pangenesis, see Geison 1969 and Endersby 2003.
6
In Variation 2: 358, CD states that his hypothesis of pangenesis involves the supposition that ‘every separate atom or unit, reproduces itself’. On the mutual affinity and aggregation of gemmules in buds and sexual elements, see ibid., pp. 374, 380–1.
7
See Variation 2: 387–8.
8
In Variation 2: 379, CD remarked that with certain kinds of plants even a minute fragment of a leaf would reproduce the whole plant. CD referred specifically to ‘a leaf of a Begonia’ in Variation 2d ed., 2: 374.
9
CD described the dormancy of gemmules, and reversion, in Variation 2: 374, 398–402, adding, ‘but there is no reason to suppose that all dormant gemmules would be transmitted and propagated for ever’ (p. 402).
10
On variability resulting from modifications of gemmules, see Variation 2: 394–7.
11
CD refers to Robert Brown and probably to William Griffith; however, the predictions alluded to have not been identified. CD had read some of Brown’s works (see Correspondence vol. 4, Appendix IV, and Marginalia 1: 94). CD had also read William Griffith’s Journals of travels in 1859 on Hooker’s recommendation; it contains numerous botanical observations and speculations (Griffith 1847–8; see Correspondence vol. 4, Appendix IV).
12
CD discussed ‘correlation of growth’ in Origin, pp. 143–50: he wrote, ‘the whole organisation is so tied together during its growth and development, that when slight variations in any one part occur, and are accumulated through natural selection, other parts become modified’ (p. 143). CD gave numerous examples of correlated variability in Variation, and discussed correlation in detail in chapter 25 (2: 319–38).

Manuscript Alterations and Comments

2.1 Bonatea & the] interl
2.1 case. Ask 2.2] altered from ‘case: ask’
2.2 ever] interl
4.2 (which] after ‘of its contents’ interl and del
4.3 or increases] interl
4.3 reproduces] after del ‘& finally’
4.6 tubes] above del ‘grains’
5.3 are capable] ‘are’ interl
6.2 of the external 6.3] ‘of the’ interl
6.3 similarly] after del ‘a’
6.3 atoms … or 6.4] interl
7.4 now] interl
7.6 of the view] interl
7.9 mutual action &] interl
8.1 or sneers] interl

Please cite as “DCP-LETT-5046,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-5046