My dear Mr Darwin

Many thanks for your kind note— Such a convert as D^r Asa Gray must be a real pleasure.¹ What strikes me so much is the way in which your doctrine accounts for & gives a vera causa of structure—so that one can almost imagine the progress of its varied development. And I find that one never passes a flower especially if it has something peculiar in form, or appendages without asking whether these are not due to crossing by insects.

I have just read & re-read with great interest Hildebrands book—² It is an excellent framework of the subject & very suggestive. Does he not go too far in suggesting that the marginal florets of many Compositæ have lost their stamens, because, as the stamens come to perfection before the pistils, and the marginal flowers open first, the stamens of the latter would be often useless?³ If there were but one flower head on a plant & but one plant in a district this might be so— But considering the infinite number of flower heads & plants contemporaneous with & suceeding one another, within any district; and considering too the probable advantage of crossing with other plants, there can be very few male florets on any plant which would not advantageously give pollen for some capable females.

Hildebrand has a capital description of Viola Tricolor, which would almost do for V. Cornuta.⁴ But in the latter the spur & anther-tails are much longer, & I think that these tails are of much use—, since when agitated by the proboscis of the insect in the spur they shake the stiff anther tube, & make the pollen fall out on the back of the lower extremity of the proboscis. It is something like the effect of the anther tails in Erica⁵ when a bee shaking the flower, jars them against the corolla.

But I will not say more about Viola, until I can get some more flowers of V. Odorata.⁶

What a long story I have written, when I only meant to thank you— Mrs Wedgwood tells me you will be in Queen Anne Street soon & I hope there to see you⁷

Believe me | Sincerely yours | T H Farrer

C Darwin Esq FRS