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Darwin Correspondence Project

From Hermann Crüger   21 January 1864


21 Janry 1864.

Dear Sir

I am sending off by this mail a small box containing a bottle with various curiosities concerning the impregnation of Orchids. There are flowers of Coryanthes, Stanhopea, Gongora & Catasetum. Further the insects which visit them a large humble bee & a very brilliantly colored Euglossa I believe.1 Further flowers of Schomburgkia & the Epidendrum mentioned in former letters which does not open & notwithstanding is always impregnated.2 One Coryanthes flower has the bee in the position it takes when forcing its way out.3 To fill up I have added some flowers of Norantea.4

With the humblebees with the pollinia of Catasetum on their back I have been unfortunate   I had three, two I tried to preserve dry which would not succeed, & the third which I put into Rum lost its pretty appendage, as happened also with one with the same organ on its back from Coryanthes.—5 The notes I have taken on these things I have incorporated into a paper on the subject which you will find in the same box.6 I have added a few remarks on the morphology of Orchids & the bearing the whole has on theory.7 I have also added a few sketches, illustrative of the subject.8 You will do with this paper what you think proper, if you think it worth publishing, it would perhaps best go to the “Natural History Review” which has some good botanists amongst its editors.9 If you think it is not fit for publication, I am still content. You will find perhaps that it is too full of Germanisms. I believe that the facts communicated in the paper are interesting although the deductions may be not approved of by all your countrymen.—

While reperusing the other day your book on Orchids,10 I recollected that bees in Germany where certain orchids are very common suffer from a disease called the “Kolbenkrankheit” “club disease” which consists of their body being beset with pollen masses to such an extent as to impede their movements. Does this disease not exist in England?—11 One of the stalks of the Epidendron sent bears flowers which I recommend to your attention, the stigmatic cavity is quite terminal surrounded besides the anthers by five lobes of the column.12 I am very sorry I did not see these flowers at an earlier stage.— In the observation of our orchids much remains to be done with regard to their insects, as the greater number of them live high up in the air the subject has its great practical difficulties   I do not think we know the insect which impregnates Stanhopea grandiflora.—13

I have failed in my experiments with native Ficus.14 Although I had them in very tight cambric bags the insects have found means to penetrate. I have not begun too late, as they were quite rudimentary & completely covered by their bracts when I tied the Bags on. But they contain much fewer insects than those which were not covered. The insects which perform the act of caprification appear not well known, the insect book I have refer the insect of the European Figs to Cynips, ours certainly do not belong to that Genus.15 I think all our Figs have their own insects, & some of them several species. In general I have had occasion again to verify what I advanced formerly that exotic figs have no insects & produce no good seeds.—16

From the paper I send you will find that some of my former notions about Catasetum were incorrect & that you had hit the thing exactly.17 I have looked in all these plants for nectar such as it is generally defined but I find none. I do not know if I wrote you in answer to your last,18 the surgeon you mention must be my friend Bradford,19 but he is certainly mistaken when he says that Catasetum tridentatum, ie the male flower bears seed.20 I consider it simply impossible for reasons specified in my paper. Monachanthus is in my opinion, as I said formerly the female form of both Catasetum & Myanthus, & it will be found that the Catasetum form, if really found on the same spike with Myanthus is the transition from Myanthus to Monachanthus.—

I forgot to tell you that I am getting a layer made for you of Norantea, which I intend to send to Kew, where you can claim it when arrived.21 I have seedlings but they take too much time to come to flower   a layer will flower in 2–3 years.—

Have you seen the paper by Mohl I refer to in my essay?22 I have lately examined the flowers of Ruellia clandestina   the small ones behave certainly as Mohl indicates in that class of dimorphic flowers he treats of.23 We have another Ruellia which does not flower now, but it also bears dimorphic flowers. I shall watch it. In General, as far as I can collect your ideas have not had the reception among German botanists which I thought I had a right to expect.24 But the younger men are nearly all given to specialities, & the older such as Mohl & others belong to the “Parti de resistance”. You will perceive that I have frankly accepted your theory, as the one which connects better than any other phenomena hitherto unconnected. On the other hand I differ from you in the explanation of the Orchidean flower, & perhaps from all living botanists.25 In general I am afraid the present generation of Botanists are shy of discussions of a theoretical description.—

I have addressed the box to the Messrs G. Dunlop & Co in Southampton,26 I know from experience that if not addressed to the care of somebody there things are apt to be lost. The bottle contains a larger humblebee, which sometimes visits Catasetum etc, but which is more timid than the other, & driven away by it. The Euglossa I find appears to have a longer tongue in the living state, how is this to be accounted for?27 If my time & money were not fully taken up by the “Amabilis”28 I should like to learn a little more about insects, I wish somebody would take up the subject in this island, there is no end of variety of them.— I need not tell you again that I am as heretofore quite at your disposal if you should like to have some other things from this island for your studies. I hope you will receive the box & contents in safety, & to learn from you how it pleases you.

Very sincerely yours | H Crüger

CD annotations

5.5 that Catasetum … paper. 5.7] double scored red crayon
Top of first page: circle, red crayon


In ‘Fertilization of orchids’, p. 154 (Collected papers 2: 151), CD said that Crüger had sent him ‘specimens of the bees, belonging to three species of Euglossa, which he saw gnawing the inside of the labellum’ of Catasetum. CD sent Crüger’s bee specimens to the British Museum for deposit, and evidently for identification (see letter to Frederick Smith, [c. 17 February 1864?]). See also n. 3, below.
See Correspondence vol. 11, letters from Hermann Crüger, 23 February 1863 and 23 April 1863. CD discussed Crüger’s information about the self-pollination of unopening flowers (later called cleistogamic flowers) in his letter to the Journal of Horticulture and Cottage Gardener, [17–24 March 1863] (Correspondence vol. 11), in ‘Fertilization of orchids’, pp. 152, 158–9 (Collected papers 2: 149, 155–6), and in Orchids 2d ed., p. 147. See also Correspondence vol. 11, letter to Hermann Crüger, 25 May [1863], and letter to John Scott, 24 March [1863].
CD mentioned Crüger’s Coryanthes specimen with the bee still within the flower in an addition to Origin 4th ed., p. 230; this passage (ibid., pp. 229–31) recounted Crüger’s observation of Coryanthes pollination from Crüger 1864 in a section entitled: ‘Cases of special difficulty on the theory of natural selection’ (ibid., pp. 224–32). CD also mentioned the Euglossa specimens sent by Crüger in his discussion of Coryanthes in ‘Fertilization of orchids’, p. 157 (Collected papers 2: 153–4), and in Orchids 2d ed., p. 175. See also letter to Daniel Oliver, 17 February [1864] and n. 11.
Crüger had discussed the pollination and form of Norantea, a member of the Marcgraviaceae, in his letter of 8 August 1863 (Correspondence vol. 11). CD had already expressed an interest in observing members of the Marcgraviaceae in his letter to Daniel Oliver, 28 March [1863] (Correspondence vol. 11).
Crüger had observed pollinia of Catasetum attaching to a bee’s back while it gnawed on the labellum of a male flower; he speculated that they were then deposited on the stigma of a female flower when the bee was similarly attracted to the labellum (see Crüger 1864, p. 129; Crüger’s observation confirmed CD’s account of Catasetum pollination in Orchids, pp. 211–13, 234–5 (see letter to Daniel Oliver, 17 February [1864] and nn. 9 and 10). The pollination of Coryanthes was described in Crüger 1864, p. 130 (see n. 3, above, and Orchids 2d ed., pp. 173–6, for CD’s published discussions of Coryanthes pollination).
CD communicated the paper (Crüger 1864) to the Linnean Society, where it was read on 3 March 1864 (see letter to Daniel Oliver, 17 February [1864]). See DAR 70: 144 and DAR 70: 145 for CD’s two annotated copies of Crüger 1864; both copies have portions cut out of them. Another heavily annotated copy is in CD’s unbound issue of the Journal of the Linnean Society (Botany) 8 (no. 31) in the Darwin Library–CUL.
Crüger argued that the adaptations and the rarity of the necessity for self-pollination that he found in orchids supported CD’s theory of transmutation, noting ‘the harmony into which it has brought so many branches of natural history hitherto unconnected’ (Crüger 1864, p. 131). For his discussion of the relation of the form of the orchid flower and its ‘history of development’ to theory, see ibid., pp. 132–5.
Crüger’s sketches included a bee, its position in a female Catasetum flower while pollinating it, and sketches of stages of development in Catasetum tridentatum (see Crüger 1864, plate 9).
See n. 6, above. The botanists on the editorial board of the Natural History Review in 1864 were Daniel Oliver and Frederick Currey, a mycologist. Crüger may also be referring to the naturalist Edward Perceval Wright. CD referred the paper to Oliver, who passed it on to George Bentham, the president of the Linnean Society (see letter from Daniel Oliver, 18 February 1864).
In Cross and self fertilisation, pp. 418–38, CD included a chapter entitled ‘The habits of insects in relation to the fertilisation of flowers’; he discussed the pollination habits of bees that he had observed, but did not mention the condition described by Crüger.
In Crüger 1864, p. 131, Crüger wrote that, in the Epidendreae, the highly viscous stigma was usually situated ‘immediately below the pollen-bed’, facilitating self-pollination. CD referred to Crüger’s observation of self-pollination in the Epidendreae in ‘Fertilization of orchids’, p. 152 (Collected papers 2: 149), and Orchids 2d ed., p. 147. See n. 2, above.
Crüger observed an insect visiting a Stanhopea and caught it with the pollen-mass on its back, but did not think that it pollinated the flower; he noted that S. grandiflora rarely bore seeds (Crüger 1864, p. 130). CD attempted to pollinate Stanhopea himself later in the year (see letter to J. D. Hooker, 3 November [1864]); he mentioned his and Crüger’s assessments of Stanhopea pollination in ‘Fertilization of orchids’, p. 153 (Collected papers 2: 150), and Orchids 2d ed., p. 171.
Crüger was already convinced that figs (Ficus) required insects for pollination, but had agreed to attempt an experiment suggested by CD to verify this (see Crüger 1851 and Correspondence vol. 11, letter from Hermann Crüger, 23 April 1863).
Caprification, a method of promoting the pollination and ripening of cultivated figs, entails hanging branches of caprifig, a wild fig, on cultivated fig trees. Gall-wasps, including the genus Cynips, then emerge from the galls of the caprifig and fly to the cultivated fig to lay eggs, carrying pollen with them.
See n. 14, above.
See Crüger 1864, p. 127. In his letter of 23 February 1863 (Correspondence vol. 11), Crüger expressed the opinion that Catasetum tridentatum and Myanthus barbatus were distinct species. CD had argued in Orchids, pp. 236–48, and ‘Three sexual forms of Catasetum tridentatum that Myanthus barbatus, Monachanthus viridis, and Catasetum tridentatum were, respectively, the hermaphrodite, female, and male forms of the same plant. For CD’s references to Crüger’s conclusion, see ‘Fertilization of orchids’, p. 154 (Collected papers 2: 151), and Orchids 2d ed., pp. 197, 200, and 202. See also letter to Daniel Oliver, 17 February [1864] and nn. 6–10.
This letter has not been found.
In his letter of 31 July 1863 (Correspondence vol. 11), Edward Bradford disputed CD’s claims about Catasetum tridentatum, informing him that when collecting and cultivating orchids in Trinidad, he had found a dried specimen of the fruit with seeds. See Orchids 2d ed., pp. 187–8.
Layering was a method of propagating plants that involved pegging down shoots, runners, or stolons to a soil surface; adventitious roots and new plants then developed. Joseph Dalton Hooker offered to send CD a Norantea specimen before Crüger’s arrived (see letter from J. D. Hooker, 9 [March] 1864).
Mohl 1863 (see Crüger 1864, p. 131). CD did read Hugo von Mohl’s paper on the small, unopening flowers (later called cleistogamic); Mohl claimed that these self-pollinating flowers contradicted CD’s assertion in Orchids, p. 359, that ‘nature … abhors perpetual self-fertilisation’ (see Mohl 1863, p. 325, and Correspondence vol. 11, letter to Daniel Oliver, 28 [November 1863]). There is an annotated copy of Mohl 1863 in the Darwin Pamphlet Collection–CUL.
For Mohl’s discussion of Ruellia clandestina, see Mohl 1863, pp. 310–11, 327.
For another report to CD on the reception of Origin in Germany, see Correspondence vol. 11, letter from Friedrich Rolle, 26 January 1863. See also Junker 1989.
While Crüger admired CD’s work on orchids, he differed from CD on some points of orchid morphology, particularly on the nature of the labellum; see Crüger 1864, pp. 132–5, for his description of orchid morphology and its relation to theoretical considerations of development. See also n. 7, above.
George Dunlop & Company were general agents and shipping agents to two Royal Mail steam-packet companies (Post Office directory of Hampshire, Dorsetshire, and Wiltshire 1867). Emma Darwin asked her son William, who lived in Southampton, to send for the parcel and forward it by rail to the Down postman (letter from Emma Darwin to W. E. Darwin, [15 February 1864], in DAR 219.1: 79).
See Crüger 1864, p. 131. The genus Euglossa is composed of bees from tropical South America that have a proboscis considerably longer than their body.
Amabilis: ‘Worthy of love’.


Collected papers: The collected papers of Charles Darwin. Edited by Paul H. Barrett. 2 vols. Chicago and London: University of Chicago Press. 1977.

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 27 vols to date. Cambridge: Cambridge University Press. 1985–.

Cross and self fertilisation: The effects of cross and self fertilisation in the vegetable kingdom. By Charles Darwin. London: John Murray. 1876.

Crüger, Hermann. 1851. Ueber Befruchtung bei den Orangen. Botanische Zeitung 9: 57–63, 73–80.

Crüger, Hermann. 1864. A few notes on the fecundation of orchids and their morphology. [Read 3 March 1864.] Journal of the Linnean Society (Botany) 8 (1865): 127–35.

‘Fertilization of orchids’: Notes on the fertilization of orchids. By Charles Darwin. Annals and Magazine of Natural History 4th ser. 4 (1869): 141–59. [Collected papers 2: 138–56.]

Junker, Thomas. 1989. Darwinismus und Botanik. Rezeption, Kritik und theoretische Alternativen im Deutschland des 19. Jahrhunderts. Stuttgart: Deutscher Apotheker Verlag.

Mohl, Hugo von. 1863. Einige Beobachtungen über dimorphe Blüthen. Botanische Zeitung 21: 309–15, 321–8.

Orchids 2d ed.: The various contrivances by which orchids are fertilised by insects. By Charles Darwin. 2d edition, revised. London: John Murray. 1877.

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.

Origin 4th ed.: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. 4th edition, with additions and corrections. By Charles Darwin. London: John Murray. 1866.

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.

Post Office directory of Hampshire, Dorsetshire, and Wiltshire: Post Office directory of Hampshire, Dorsetshire, and Wiltshire. Post Office directory of Dorsetshire, Wiltshire, and Hampshire, including the Isle of Wight. London: Kelly & Co. 1848–75.

‘Three sexual forms of Catasetum tridentatum’: On the three remarkable sexual forms of Catasetum tridentatum, an orchid in the possession of the Linnean Society. By Charles Darwin. [Read 3 April 1862.] Journal of the Proceedings of the Linnean Society (Botany) 6 (1862): 151–7. [Collected papers 2: 63–70.]


Sends his MS of orchid paper ["A few notes on the fecundation of orchids and their morphology", J. Linn. Soc. Lond. (Bot.) 8 (1865): 127–35] for CD to send to an editor.

CD was right about Catasetum sexes.

Ficus experiments fail.

Letter details

Letter no.
Hermann Crüger
Charles Robert Darwin
Sent from
Source of text
DAR 161: 278
Physical description
4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 4394,” accessed on 23 October 2021,

Also published in The Correspondence of Charles Darwin, vol. 12