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Darwin Correspondence Project

To George Bentham   3 February [1862]1

Down Bromley Kent

Feb. 3d.

Dear Bentham

As you so kindly helped me before on Dimorphism, will you forgive me begging for a little further information, if in your power to give it.2

The case is that of the Melastomads with 8 stamens, on which I have been experimenting.3 I am perplexed by opposed statements: Lindley says the stamens which face the petals are sterile;4 Wallich says in Oxyspora paniculata, that the stamens which face the sepals are destitute of pollen:5 I find plenty of apparently good pollen in both sets of stamens in Heterocentron, Monochætum & Centradenia.6 Can you throw any light on this?

But there is another point on which I am more anxious for information: please look at enclosed miserable diagram:7 I find that the pollen of the yellow petal-facing stamens produce more than twice as much seed as the pollen of the purple sepal-facing stamens.8 This is exactly opposed to Lindley’s statement, viz that the petal-facing stamens are sterile. But I cannot at present believe that the case has any relation to abortion; it is hardly possible to believe that the longer & very curious stamens, which face the sepals in this Heterocentron are tending to be rudimentary, though their pollen applied to their own flowers produce so much less seed.— It is conformable with what we see in Primula that the sepal-facing anthers which in the plant seen by me, stood quite close on each side of the stigma should have been rendered less fitted to fertilise the stigma, than the stamens on the opposite side of the flower. Hence the suspicion has crossed me, that if many plants of the Heterocentron roseum were examined, half would be found with the pistil nearly upright, instead of being rectangularly bent down, as shown in the Diagram. Or, if position of pistil is fixed, that in half the plants the petal-facing stamens would bend down & in the other half of the plants the sepal-facing stamens would bend down as in the diagram.— I suspect the former case, as in Centradenia I find the pistil nearly straight.—9 Can you tell me? Can the name Heterocentron have any reference to such diversity? Would it be asking too great a favour to ask you to look at dried specimens of Heterocentron roseum (which would be best) or of Monchætum or any 8-stamened Melastomatid, of which you have specimens from several localities (as this would ensure specimens having been taken from distinct plants) & observe whether the pistil bends differently, or stamens differently in different plants.— You will at once see that if such were the fact, it would be a new form of dimorphism, & would open up a large field of enquiry with respect to the potency of the pollen in all plants which have two sets of stamens, viz longer & shorter.

Can you forgive me for troubling you at such unreasonable length? But it is such waste of time to experiment without some guiding light. I do not know whether you have attended particularly to Melastomas— if you have not, perhaps Hooker or Oliver may have done so.10

I should be very grateful for any information, as it will guide future experiments.

Yours very sincerely | C. Darwin

Do you happen to know when there are only 4 stamens, whether it is the petal- or sepal facers which are preserved? & whether in the 4-stamened forms the pistil is rectangularly bent or is straight?


The year is established by the relationship to the letter to J. D. Hooker, 9 February [1862], and to an observational note on Heterocentron roseum in DAR 205.8: 46, dated 3 February 1862. See also nn. 6 and 8, below.
Following the presentation of CD’s account of the two forms in Primula at a meeting of the Linnean Society of London on 21 November 1861, Bentham had provided CD with additional instances of dimorphism (see Correspondence vol. 9, letters from George Bentham, 26 November 1861 and 29 November 1861).
CD had begun crossing experiments on the Melastomataceae in October 1861, believing that plants of this family might exhibit a novel form of dimorphism. Although he continued to work on the family throughout 1862 and 1863, making extensive notes (see DAR 205.8), he reached no definite conclusion and did not publish on the subject (see Cross and self fertilisation, p. 298 n., and ML 2: 292–3).
N. Wallich 1830–1, 1: 78. There is a note by CD recording this reference in DAR 205.8: 61.
There are notes by CD recording his observations of the pollen of Heterocentron roseum (dated 28 October 1861), Monochaetum ensiferum (dated 15 January 1862), and Centradenia grandiflora and C. floribunda (dated 2 January [1862]) in DAR 205.8: 44, 22, and 16 v. He summarised his findings in the three genera mentioned here, together with Nathaniel Wallich’s findings in Oxyspora paniculata (bristletips), on the reverse of an experimental note dated 3 February 1862 (DAR 205.8: 46; see n. 8, below).
The diagram has not been located, but a diagram of Heterocentron roseum included in a note by CD dated 29 October 1861 labels petal- and sepal-facing anthers (DAR 205.8: 45). See also the diagram in the letter to Asa Gray, 16 February [1862].
CD refers to the results of his first pollination experiment with a melastomaceous plant, carried out on Heterocentron roseum between October 1861 and January 1862. The results of this experiment are recorded in a note dated 3 February 1862 (DAR 205.8: 46). See also letter to Asa Gray, 22 January [1862] and n. 13.
There is a note recording this observation, dated 2 January [1862], in DAR 205.8: 16 r.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 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.

Lindley, John. 1836. A natural system of botany; or, a systematic view of the organisation, natural affinities, and geographical distribution, of the whole vegetable kingdom; together with the uses of the most important species in medicine, the arts, and rural or domestic economy. 2d ed. London.

ML: More letters of Charles Darwin: a record of his work in a series of hitherto unpublished letters. Edited by Francis Darwin and Albert Charles Seward. 2 vols. London: John Murray. 1903.


Asks GB’s help to clear up discrepancies between his and John Lindley’s observations on pollination of Melastomataceae.

Letter details

Letter no.
Charles Robert Darwin
George Bentham
Sent from
Source of text
Royal Botanic Gardens, Kew (Bentham Correspondence, Vol. 3, Daintree–Dyer, 1830–1884, GEB/1/3: f. 694–6)
Physical description
ALS 6pp

Please cite as

Darwin Correspondence Project, “Letter no. 3437,” accessed on 23 June 2024,

Also published in The Correspondence of Charles Darwin, vol. 10