My dear Sir

I have just rec^d your letter of Aug. 2^nd & am as usual astonished at the number of interesting points which you observe. It is quite curious how by coincidence you have been observing the same subjects that have lately interested me.²

Your case of the Notylia is quite new to me; but it seems analogous with that of Acropera, about the sexes of which I blundered greatly in my book.³ I have got an Acropera now in flower & have no doubt that some insect with a tuft of hairs on its tail removes by the tuft the pollinia, & inserts the little viscid cap & the long pedicel into the narrow stigmatic cavity, & leaves it there with the pollen-masses in close contact with, but not inserted into, the stigmatic cavity. I find I can thus fertilize the flowers; & so I can with Stanhopea, & I suspect that this is the case with your Notylia.⁴ But I have lately had an orchid in flower, viz. Acineta, which I could not any how fertilize.⁵ D^r Hildebrand lately wrote a paper shewing that with some orchids the ovules are not mature & are not fertilized until months after the pollen-tubes have penetrated the column; & you have independently observed the same fact, which I never suspected in the case of Acropera.⁶ The column of such orchids must act almost like the Spermatheca of insects. Your Orchis with 2 leaf-like stigmas is new to me; but I feel guilty at your wasting your valuable time in making such beautiful drawings for my amusement.⁷

Your observations on those plants being sterile which grow separately or flower earlier than others are very interesting to me. They w^d be worth experimenting on with other individuals: I shall give in my next book several cases of individual plants being sterile with their own pollen. I have actually got on my list Escholtzia for fertilizing with its own pollen, though I did not suspect it w^d prove sterile, & I will try next summer.⁸ My object is to compare the rate of growth of plants raised from seed fertilized by pollen from the same flower & by pollen from a distinct plant & I think from what I have seen I shall arrive at interesting results.⁹ D^r Hildebrand has lately described a curious case of Corydalis cava, which is quite sterile with its own pollen, but fertile with pollen of any other individual plant of the species.¹⁰ What I meant in my paper on Linum about plants being dimorphic in function alone was that they sh^d be divided into two equal bodies functionally but not structurally different.¹¹ I have been much interested by what you say on seeds which adhere to the valves being rendered conspicuous: you will see in the new Edit. of the origin why I have alluded to the beauty & bright colours of fruit;¹² after writing this, it troubled me that I remembered to have seen brilliantly coloured seed, & your view occurred to me. There is a species of Peony in which the inside of the pod is crimson & the seeds dark purple. I had asked a friend to send me some of these seeds, to see if they were covered with any thing which c^d prove attractive to birds.¹³ I rec^d some seeds the day after receiving your letter; & I must own that the fleshy covering is so thin that I can hardly believe it w^d lead birds to devour them; & so it was in an analogous case with Passiflora gracilis.¹⁴ How is this in the cases mentioned by you? The whole case seems to me rather a striking one.

I wish I had heard of Mikania being a leaf-climber before your paper was printed; for we thus get a good gradation from M. scandens to Mutisia with its little modified leaf-like tendrils.¹⁵ I am glad to hear that you can confirm (but render still more wonderful) Haeckel’s most interesting case of Liriope: Huxley told me that he thought that the case w^d somehow be explained away.¹⁶

As for Agassiz & his glaciers in the valley of the Amazons, it seems to me sheer madness, as it does likewise to Lyell; the evidence being wholly insufficient.¹⁷ Prof. Asa Gray tells me that A. started with the determination to prove that the whole world had been covered with ice in order to annihilate all Darwinian views.¹⁸

I hope I have not troubled you with this long letter & believe me yours very sincerely

Charles Darwin