Dear Sir

I thank you for your very interesting letter;² I must answer as briefly as I can, for I have a heap of other letters to answer. I strongly advise you to follow up & publish your observations on the pollen-tubes of orchids; they promise to be very interesting.³ If you could prove what I only conjectured (from state of utriculi in Rostellum & in stigma of Catasetum & Acropera) that the utriculi somehow induce or are connected with penetration of pollen-tubes you will make an important physiological discovery.⁴ I will mention, as worth your attention (& what I have anxiously wished to observe, if time had permitted & still hope to do) viz the state of tissues or cells of stigma in an utterly sterile hybrid, in comparison with the same in fertile parent-species: to test these cells, immerse stigmas for 48 hours in spirits of wine; I sh^d. expect in hybrids that the cells would not show coagulated contents. It would be interesting discovery to show difference in female organs of hybrids & pure species. Anyhow it is worth trial & I recommend you to make it & publish if you do.—⁵

The pollen-tubes directing themselves to stigma is also very curious; though not quite so new; but well worth investigation when you get Cattleya &c in flower.—⁶ I say not so new; for remember small flower of Viola & Oxalis; or better, see Bibliography of Nat. Hist. Review Part VIII. p. 419—(Oct 1862) for quotation from M. Baillon, on pollen tubes finding way from anthers to stigma in Helianthemum.⁷ I sh^d. doubt gum getting solid from continued secretion. Why not sprinkle fresh Plaister of Paris & make impenetrable crust?⁸ You might modify experiment by making little hole on one lower corner, & see if tubes find it out.— See in my future paper on Linum pollen & stigma recognising each other.—⁹ If you will tell me that pollen smells the stigma I will try & believe you; but I will not believe the Frenchman (I forget who) who says that Stigma of Vanilla actually attracts mechanically by some unknown force the solid pollen-masses to it!¹⁰

Read Asa Gray in 2^d Review of my Orchis Book on pollen of Gymnadenia penetrating rostellum;¹¹ I can, if you like, lend you these Reviews; but they must be returned.— R. Brown, I remember, says pollen-tubes separate from grains before the lower ends of tubes reach ovules.—¹² I saw, & was interested by, abstract of your Drosera paper:¹³ we have been at very much same work.—

With respect to bud-variation: perhaps it would give you the least trouble first to send me mere list. I have devoted whole Chapter to subject.¹⁴ Perhaps it will be best to specify cases which interest me most—variation by modified buds as bulbs or tubers—or underground as suckers—anything on inheritance from seed of the varying buds—, whether parents are crossed plants, & whether the variation is case of Reversion. Of course the more marked the variation is so much better. I do not care for mere zoned leaves, unless something unusual about them.

I have hitherto just alluded to every case of change in colour in flower, especially if accompanied by any other change. M^r Salter & M^r Rivers are aiding me.—¹⁵

With respect to Ferns I am so ignorant that I hardly know what to do. Am I right in supposing (probably I am wrong) that a spore (whether spore be unfertilised ovule or bud) from a variagted branch produces a thallus, & this produces the two sexual individuals & from their union a variegated fern is produced; if so, the case would not come under variation independent of sexual union. Please briefly illuminate my ignorance.—¹⁶

M^r. Bridgman sent me his paper.—¹⁷

Asa Gray has sent me a few white & red seed of N. England Popping very small seeded maize;¹⁸ shall you experiment on this; if so these would be good to cross with some large kind of different colour.— Shall I send??

Yesterday I had very kind letter from M^r I. Anderson Henry, of Hay Lodge, Trinity offering to try any experiment for me.¹⁹ I have suggested peloric flowers & pollen of short stamens of Pelargonium.—²⁰ Please tell me in strict confidence whether you think him a good observer; from his short papers, I say to you in confidence that I doubt it.—²¹ You will see that it is of paramount importance for me not to waste time in suggesting experiments &c & asking for information from an inaccurate observer.—

Excuse this hurried letter. | Dear Sir | Yours very faithfully | Chs. Darwin

I hardly know what to say on your view of male & female organs & variability.—²² I must think more over it. But I was amused by finding the other day in my Portfolio devoted to Bud-variation, a slip of paper dated June 1860, with some such words as these “May not permanence of grafted buds be due to the two sexual elements, derived from different part not having come into play?”²³ I had utterly forgotten, when I read your paper, that any analogous notion had ever passed through my mind—nor can I now remember, but the slip shows me that it had.—