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?