because of] continued secretion. Why not sprinkle fresh plaster of Paris and make impenetrable crust? (637/1. The suggestion that the stigma should be covered with a crust of plaster of Paris, pierced by a hole to allow the pollen-tubes to enter, bears a resemblance to Miyoshi's experiments with germinating pollen and fungal spores. See "Pringsheim's Jahrbucher," 1895; "Flora," 1894.) You might modify experiment by making little hole in one lower corner, and see if tubes find it out. See in my future paper on Linum pollen and stigma recognising each other. If you will tell me that pollen smells the stigma I will try and 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! Read Asa Gray in 2nd Review of my Orchis book on pollen of Gymnadenia penetrating rostellum. 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. I saw, and was interested by, abstract of your Drosera paper (637/2. A short note on the irritability of Drosera in the "Trans. Bot. Soc. Edin." Volume VII.); we have been at very much the same work.
LETTER 638. TO J. SCOTT. Down, February 16th [1863].
Absence from home has prevented me from answering you sooner. I should think that the capsule of Acropera had better be left till it shows some signs of opening, as our object is to judge whether the seeds are good; but I should prefer trusting to your better judgment. I am interested about the Gongora, which I hope hereafter to try myself, as I have just built a small hot-house.
Asa Gray's observations on the rostellum of Gymnadenia are very imperfect, yet worth looking at. Your case of Imatophyllum is most interesting (638/1. A sucker of Imatophyllum minatum threw up a shoot in which the leaves were "two-ranked instead of four-ranked," and showed other differences from the normal.--"Animals and Plants," Edition II., Volume I., page 411.); even if the sport does not flower it will be worth my giving. I did not understand, or I had forgotten, that a single frond on a fern will vary; I now see that the case does come under bud-variation, and must be given by me. I had thought of it only as proof [of] inheritance in cryptogams; I am much obliged for your correction, and will consult again your paper and Mr. Bridgeman's. (638/2. The facts are given in "Animals and Plants," Edition II., Volume I., page 408.) I enclose varieties of maize from Asa Gray. Pray do not thank me for trusting you; the thanks ought to go the other way. I felt a conviction after your first letter that you were a real lover of Natural History.
If you can advance good evidence showing that bisexual plants are more variable than unisexual, it will be interesting. I shall be very glad to read the discussion which you are preparing. I admit as fully as any one can do that cross-impregnation is the great check to endless variability; but I am not sure that I understand your view. I do not believe that the structure of Primula has any necessary relation to a tendency to a dioecious structure, but seeing the difference in the fertility of the two forms, I felt bound unwillingly to admit that they might be a step towards dioeciousness; I allude to this subject in my Linum paper. (638/3. "Linn. Soc. Journal," 1863.) Thanks for your answers to my other queries. I forgot to say that I was at Kew the other day, and I find that they can give me capsules of several Vandeae.
LETTER 639. TO J. SCOTT. Down, March 24th [1863].
Your letter, as every one you have written, has greatly interested me. If you can show that certain individual Passifloras, under certain known or unknown conditions of life, have stigmas capable of fertilisation by pollen from another species, or from another individual of its own species, yet not by its own individual pollen (its own individual pollen being proved to be good by its action on some other species), you will add a case of great interest to me; and which in my opinion would be quite worth your publication.