To Daniel Oliver   28 [November 1863]1

Down

28th

Dear Oliver

Your note has interested me much.—2 But I cannot look to notes on Fumitories, have not near strength enough.3 These plants are fertile in large degree without insect but are all (or nearly all) manifestly adapted to visits of insects,4 which favour & increase their fertility— But I must write no more.—

I shall be very curious to read sometime Hugo von Mohl on the little flowers.5 I did some work on them & on violets this summer.6

You may rely that perfect flowers of violets except V. tricolor are fertile only when visited by insects: I marked flowers visited by Bees & prevented Bees visiting others &c—7 The imperfect flowers are of course fertile without insect-visits—

Yours very sincerely | C. Darwin

How curious about the pods.—8

The hydrostatic movement must be sometime like that of the pollinia in orchids.—9

1
The date is established by the relationship between this letter and the letter from Daniel Oliver, 27 November 1863.
3
See letter from Daniel Oliver, 27 November 1863 and nn. 8–10. CD’s botanical notes on Fumariaceae, dated from 1857 to 1863, are in DAR 76: B13–21.
4
Oliver quoted this sentence in his review of works on dimorphic flowers ([Oliver] 1864b, p. 246). For CD’s observations on Fumariaceae, see the letter from Daniel Oliver, 27 November 1863 and n. 8.
5
CD began observing the small, unopening flowers (later called cleistogamic) of Oxalis and Viola during the spring of 1862 (see, for example, Correspondence vol. 10, letter to Asa Gray, 10–20 June [1862] and n. 24). He made additional observations in 1863 (see n. 6, below). CD commented on Mohl 1863 in his manuscript of ‘Three forms of Lythrum salicaria’ (DAR 27.2: 44a–b), with a shorter reference to his observations only appearing in the published version, p. 196 (Collected papers 2: 128). In Forms of flowers he also referred to Mohl’s observations on cleistogamy (pp. 314, 320–1, 330), only disagreeing with Mohl’s insistence that the open flowers on cleistogamous plants were sterile. There is an annotated copy of Mohl 1863 in the Darwin Pamphlet Collection–CUL.
6
For CD’s 1863 notes on Oxalis acetosella, see DAR 109: B6–7 and DAR 111: A46. For his 1863 notes on Viola, see DAR 111: A5–12. See also letter to Asa Gray, 31 May [1863] and n. 19.
7
Some of CD’s observations on Viola tricolor are preserved in DAR 111: A27. See also Cross and self fertilisation, pp. 123–8.
9
In Orchids, pp. 335–9, CD described the movement of some orchid pollinia, and the disc to which they are attached, when exposed alternately to air and water.

Manuscript Alterations and Comments

3.1 except V. tricolor] interl
3.3 The imperfect … insect-visits—] added

Please cite as “DCP-LETT-4350,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-4350