To Fritz Müller   20 September [1865]1

Down. | Bromley. | Kent. S.E.

Sep. 20.

My dear Sir

I am very much obliged for your interesting letter written in such wonderfully good English about climbing plants.2 The case of Haplolophium is new to me & I am glad to have seen the tendril of Strychnos.3 I do not suppose I shall attend any more to climbing plants, but I shd like to hear if you ever meet with 2 species of the same genus, twining in opposite directions4   I should further like much to hear whether any twiners can ascend thick trunks.5 How wonderfully rich you are in climbing plants! As I see you know much more about plants than I do, I sent off by the post yesterday a German copy of my Orchis book & two papers on Dimorphism.6 The latter will I think interest you & perhaps one Chapter, for instance that on Catasetum in my Orchis book wd be worth your reading to shew how perfect the contrivances are.7 Your remarks on the spines in Acasta are quite new to me & seem very probable.8 In my last letter I alluded to Anelasma; I am not sure, but I think I speculated on the relation of the branching filaments to cement tubes, but rejected the idea on account of the apparent continuity of the filaments with the outer membrane of the Capitulum.9 Perhaps I may have made some mistake for your view now seems to me probable.10 My specimen unfortunately had been removed out of the Sharks flesh.

The difficulty which you quote from A. Agassiz on the embryology of the Echinodermata is quite beyond me & I shd think wd be just the subject for you.11 Any how the difficulty is quite as great to L. Agassiz on his views of classification as to us on descent & modification, & that is some comfort.12

Does it not often strike you that Natural History is rendered extremely interesting by such views as we both hold. This frequently occurred to me when reading your work. I am sorry to say my health keeps so weak that I am not able to do any scientific work. If you write again I shd very much like to hear whether you intend to remain long at Desterro & how you like your new home   I have always heard the Island is most beautiful13   Have you ever read my Journal of Researches or Travels & if not wd you like to have a copy.14

With sincere respect, | My dear Sir | yours very faithfully | Ch. Darwin

LS

1
The year is established by the relationship between this letter and the letter from Fritz Müller, 12 August 1865.
2
See letter from Fritz Müller, 12 August 1865 and n. 1, and letter from Fritz Müller, [12 and 31 August, and 10 October 1865]. CD had not yet received Müller’s second letter on twining plants of 31 August 1865 (see letter to Fritz Müller, 17 October [1865]).
3
The information on Haplolophium and Strychnos is contained in the section of the 12 August 1865 letter from Fritz Müller that was later published by CD in the Journal of the Linnean Society (Botany) 9 (1866): 344–9 (see Müller 1865b and letter from Fritz Müller, [12 and 31 August, and 10 October 1865] and n. 1; see also the letter from Fritz Müller, 12 August 1865 and n. 11). Müller included drawings of some of the climbing plants he described in his letters to CD (see letter to Fritz Müller, 17 October [1865]), and some of these were reproduced in Müller 1865b. He also sent CD specimens of Haplolophium, Strychnos, and Caulotretus; these are in DAR 142: 44–6.
4
In ‘Climbing plants’, p. 20, CD had noted that there was no known instance of two species of the same genus twining in opposite directions. CD added the information he received from Müller on this topic to Climbing plants 2d ed., p. 36 n. (see letter from Fritz Müller, [12 and 31 August, and 10 October 1865] and nn. 16–18).
5
CD’s observations on twiners ascending the trunks of trees are in ‘Climbing plants’, pp. 21–2 (see letter from Fritz Müller, [12 and 31 August, and 10 October 1865] and n. 19).
6
CD refers to Bronn trans. 1862, ‘Two forms in species of Linum’, and ‘Three forms of Lythrum salicaria’; the last is on trimorphism.
7
Catasetum is discussed in chapter 6 of Orchids, pp. 211–85 (Bronn trans. 1862, pp. 130–53). For more on pollination in Catasetum, see Correspondence vol. 12, letter from Hermann Crüger, 21 January 1864, and letter to Daniel Oliver, 17 February [1864].
8
The letter from Müller of 12 August 1865 is incomplete. The section of the letter containing Müller’s observation on spines in the barnacle Acasta has not been found. Acasta, classified by CD as a subgenus of Balanus, is a barnacle usually found attached to sponges (see Living Cirripedia (1854), pp. 176–7; for the modern classification, see Newman 1996, pp. 502–3). CD had described the cirri in many species of Acasta as remarkable because of the existence of spines on the fourth pair of cirri (Living Cirripedia (1854), p. 306). Müller’s observation almost certainly concerned his discovery of a species of sponge-dwelling Balanus, Balanus armatus, that had spines on the third pair of cirri. In a letter to Max Johann Sigismund Schultze of 10 November 1864, Müller had discussed his observations on this species (the letter is published in Möller ed. 1915–21, 2: 58). Müller’s description of B. armatus was published in Müller 1867; an English version appeared the next year (Müller 1868a). In the article, Müller referred to the spines as an example of analogous variation similar to the air-breathing apparatus in some crabs that he had observed earlier (Müller 1867, pp. 344–5, and Müller 1868a, pp. 404–5; see also letter to Fritz Müller, 10 August [1865] and n. 5).
9
In Living Cirripedia (1851), pp. 169–80, CD had noted that he found neither cement nor cement glands in Anelasma squalicola, but concluded that the organism probably became attached in the first instance in the normal way, that is by cement glands, but then was ‘retained in its place, by being so deeply imbedded in the shark’s body, and perhaps by the root-like branched filaments’ (ibid., p. 174). CD eventually concluded that the filaments were not modified cement ducts but originated in the outer membrane, which he described as continuous from the capitulum (the main body of the barnacle, which remained on the exterior of the host) to the peduncle (the stalk-like portion, which became embedded at the site of attachment); see ibid., pp. 173, 380–1, and pl. IV, figs. 2 and 3. CD did not encounter Rhizocephala when he worked on barnacles, but, after reading Müller 1864, he had suggested to Müller that Anelasma might represent a connecting link between Rhizocephala and other cirripedes (see letter to Fritz Müller, 10 August [1865] and n. 7). CD evidently reconsidered the origin of the branched filaments of Anelasma, seeing them as an intermediate stage between the cement ducts of other cirripedes and the root-like tubes in Rhizocephala.
10
Müller’s observations on the relation between branched filaments in Anelasma and the root-like tubes of Rhizocephala are in the missing section of the letter from Fritz Müller, 12 August 1865 (see letter from Fritz Müller, 10 October 1865). Since Müller would not have received CD’s letter of 10 August [1865] when he wrote his own letter to CD on 12 August 1865, it appears that the possibility of Anelasma as a connecting link occurred to each of them independently. When Für Darwin (Müller 1864) was translated into English, some additional material was added, including Müller’s hypothesis on the relation of branched filaments to cement ducts and root-like tubes (see enclosure to letter from Fritz Müller, 22 April 1868, Calendar no. 6140, and Dallas trans. 1869, pp. 135–40).
11
The section of Müller’s letter of 12 August 1865 in which he discussed Alexander Agassiz’s observations on echinoderm embryology has not been found. Agassiz’s letter to Müller, 9 March 1865, which contains these observations, is reproduced in Winsor 1976, pp. 189–94. In Origin, p. 449, CD had argued that two groups of animals that passed through similar embryonic stages did so because they shared a common ancestor, and concluded: ‘community in embryonic structure reveals community of descent’. The problem Agassiz raised was the similarity in the larvae of sea urchins and brittle stars (Echinoids and Ophiurans). Agassiz pointed out that there was nothing in the adult forms to suggest any affinity and moreover that if they did share a common ancestor it was surprising that there were no connecting links in the fossil record, given that, with few exceptions, one would expect their skeletons to be well-preserved. Müller admitted in his reply (letter from Fritz Müller to Alexander Agassiz, 29 June 1865, in Möller ed. 1915–21, 2: 64–7) that the case was a real difficulty for Darwinian theory (see Winsor 1976, pp. 152–4 and passim, for a more detailed analysis of the case).
12
CD refers to Louis Agassiz and probably to his ‘Essay on classification’ (J. L. R. Agassiz 1857–62, vol. 1), in which Agassiz based his system of classification on embryological as well as adult morphological similarities. In Origin, p. 449, CD had referred to Agassiz’s belief that it was a law of nature that ‘ancient and extinct forms of life should resemble the embryos of their descendants, —our existing species’. The existence of similar larval forms in apparently disparate adult genera was therefore no more explicable within Agassiz’s system based on ‘prophetic’ (embryonic) types (see Winsor 1976, pp. 146–8) than within a Darwinian one based on common descent. CD’s annotated presentation copy of J. L. R. Agassiz 1857–62, vol. 1, is in the Darwin Library–CUL; see also Marginalia 1: 9–11.
13
Destêrro (now called Florianópolis) is on Santa Catarina Island, just off the coast of south-eastern Brazil (Columbia gazetteer of the world).
14
CD refers to the Journal of researches. While on the Beagle voyage, CD travelled down the eastern coast of South America, stopping in Rio de Janeiro and exploring parts of the interior of Brazil (see Journal of researches, pp. 21–43).

Manuscript Alterations and Comments

1.1 written … English 1.2] interl in CD’s hand

Please cite as “DCP-LETT-4895,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-4895