hy 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 ar