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Darwin Correspondence Project

To T. F. Cheeseman   9 September [1873]1

Down, | Beckenham, Kent.

Sept 9th

Dear Sir

I thank you for having sent me your extremely interesting paper.— I can entertain no doubt that your explanation is as correct, as your account is clear.2

The case is strictly analogous, though the result effected by very different means, as in Cypripedium;—not as I incorrectly described it at first but as described by H. Müller viz. that the insect is forced from the inflexed rim of the labellum to crawl out by the 2 apertures close to the anthers & stigma.—3 Your case is much more curious.—4

With my best thanks | I remain | Dear Sir | Yours faithfully | Ch. Darwin

I tried Cypripedium with a minute bee & saw the whole process, as you did with your orchid.—


The year is established by the relationship between this letter and the letter from T. F. Cheeseman, 27 June 1873.
Cheeseman had sent CD a copy of his article ‘On the fertilisation of the New Zealand species of Pterostylis’ (Cheeseman 1872). See letter from T. F. Cheeseman, 27 June 1873 and nn. 1 and 3.
CD had originally suggested that Cypripedium, with its slipper-like shape, was fertilised by an insect inserting its proboscis through slits in the labellum and thereby brushing against the sticky pollen of the anthers and transferring it to the stigma (see Orchids, pp. 271–5). In Orchids 2d ed., pp. 230–1, CD adopted Hermann Müller’s explanation that small bees entered the labellum at the top and, unable to escape by this route, were forced to exit via the small slits near the anthers and stigma (see H. Müller 1873, p. 76).
Cheeseman observed that the labellum of Pterostylis trullifolia (now Diplodium trullifolium) sprang up to close the flower when triggered by an insect landing on it. The trapped insect could crawl out only through a narrow passage where it came into contact with the pollen masses at the top of the column. On being trapped in another plant, the insect deposited this pollen on the adhesive stigma before collecting more pollen as it exited the flower. CD added Cheeseman’s description of the fertilisation mechanism of Pterostylis trullifolia to Orchids 2d ed., pp. 86–8.


Thanks TFC for his extremely interesting paper ["On the fertilisation of the New Zealand species of Pterostyles", Trans. & Proc. N. Z. Inst. 5 (1872): 352–7]. Has no doubt his explanation [of the fertilisation mechanism] is correct. The case is analogous to that of the Cypripedium though TFC’s case is much more curious.

Letter details

Letter no.
Charles Robert Darwin
Thomas Frederick Cheeseman
Sent from
Source of text
Auckland War Memorial Museum Library - Tāmaki Paenga Hira (T. F. Cheeseman Papers MS-58)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9048,” accessed on 13 December 2017,

Also published in The Correspondence of Charles Darwin, vol. 21