For the part relating to Verbascum see the "Variation of Animals and Plants," Edition II., 1875, Volume II., page 83. The point is that the white and yellow flowered plants which occur in two species of Verbascum are undoubted varieties, yet "the sterility which results from the crossing of the differently coloured varieties of the same species is fully as great as that which occurs in many cases when distinct species are crossed."
The sterility of the long-styled form (B) of Linum grandiflorum, with its own pollen is described in "Forms of Flowers," Edition II., page 87: his conclusions on the short-styled form (A) differ from those in the present letter.)
September 28th [1861].
I am going to beg for help, and I will explain why I want it.
You offer Cypripedium; I should be very glad of a specimen, and of any good-sized Vandeae, or indeed any orchids, for this reason: I never thought of publishing separately, and therefore did not keep specimens in spirits, and now I should be very glad of a few woodcuts to illustrate my few remarks on exotic orchids. If you can send me any, send them by post in a tin canister on middle of day of Saturday, October 5th, for Sowerby will be here.
Secondly: Have you any white and yellow varieties of Verbascum which you could give me, or propagate for me, or LEND me for a year? I have resolved to try Gartner's wonderful and repeated statement, that pollen of white and yellow varieties, whether used on the varieties or on DISTINCT species, has different potency. I do not think any experiment can be more important on the origin of species; for if he is correct we certainly have what Huxley calls new physiological species arising. I should require several species of Verbascum besides the white and yellow varieties of the same species. It will be tiresome work, but if I can anyhow get the plants, it shall be tried.
Thirdly: Can you give me seeds of any Rubiaceae of the sub-order Cinchoneae, as Spermacoce, Diodia, Mitchella, Oldenlandia? Asa Gray says they present two forms like Primula. I am sure that this subject is well worth working out. I have just almost proved a very curious case in Linum grandiflorum which presents two forms, A and B. Pollen of A is perfectly fertile on stigma of A. But pollen of B is absolutely barren on its own stigma; you might as well put so much flour on it. It astounded me to see the stigmas of B purple with its own pollen; and then put a few grains of similar-looking pollen of A on them, and the germen immediately and always swelled; those not thus treated never swelling.
Fourthly: Can you give me any very hairy Saxifraga (for their functions) [i.e. the functions of the hairs]?
I send you a resume of my requests, to save you trouble. Nor would I ask for so much aid if I did not think all these points well worth trying to investigate.
My dear old friend, a letter from you always does me a world of good. And, the Lord have mercy on me, what a return I make.
LETTER 602. TO J.D. HOOKER. Down, October 4th [1861].
Will you have the kindness to read the enclosed, and look at the diagram. Six words will answer my question. It is not an important point, but there is to me an irresistible charm in trying to make out homologies. (602/1. In 1880 he wrote to Mr. Bentham: "It was very kind of you to write to me about the Orchideae, for it has pleased me to an extreme degree that I could have been of the least use to you about the nature of the parts."-- "Life and Letters," III., page 264.) You know the membranous cup or clinandrum, in many orchids, behind the stigma and rostellum: it is formed of a membrane which unites the filament of the normal dorsal anther with the edges of the pistil. The clinandrum is largely developed in Malaxis, and is of considerable importance in retaining the pollinia, which as soon as the flower opens are quite loose.
The appearance and similarity of the tissues, etc., at once gives suspicion that the lateral membranes of the clinandrum are the two other and rudimentary anthers, which in Orchis and Cephalanthera, etc., exist as mere papillae, here developed and utilised.