Loddigesii, which will bear testimony to the veracity of the remarks I have ventured to lay before you.
LETTER 632. TO J.D. HOOKER. Down, 18th [November 1862].
Strange to say, I have only one little bother for you to-day, and that is to let me know about what month flowers appear in Acropera Loddigesii and luteola; for I want extremely to beg a few more flowers, and if I knew the time I would keep a memorandum to remind you. Why I want these flowers is (and I am much alarmed) that Mr. J. Scott, of Bot. Garden of Edinburgh (do you know anything of him?) has written me a very long and clever letter, in which he confirms most of my observations; but tells me that with much difficulty he managed to get pollen into orifice, or as far as mouth of orifice, of six flowers of A. Loddigesii (the ovarium of which I did not examine), and two pods set; one he gathered, and saw a very few ovules, as he thinks, on the large and mostly rudimentary placenta. I shall be most curious to hear whether the other pod produces a good lot of seed. He says he regrets that he did not test the ovules with chemical agents: does he mean tincture of iodine? He suggests that in a state of nature the viscid matter may come to the very surface of stigmatic chamber, and so pollen- masses need not be inserted. This is possible, but I should think improbable. Altogether the case is very odd, and I am very uneasy, for I cannot hope that A. Loddigesii is hermaphrodite and A. luteola the male of the same species. Whenever I can get Acropera would be a very good time for me to look at Vanda in spirits, which you so kindly preserved for me.
LETTER 633. TO J. SCOTT.
(633/1. The following is Darwin's reply to the above letter from Scott. In the first edition of "Fertilisation of Orchids" (page 209) he assumed that the sexes in Acropera, as in Catasetum, were separate. In the second edition (page 172) he writes: "I was, however, soon convinced of my error by Mr. Scott, who succeeded in artificially fertilising the flowers with their own pollen. A remarkable discovery by Hildebrand (633/2. "Bot. Zeitung," 1863 and 1865.), namely, that in many orchids the ovules are not developed unless the stigma is penetrated by the pollen-tubes...explains the state of the ovarium in Acropera, as observed by me." In regard to this subject see Letter 608.)
Down, November 12th, 1862.
I thank you most sincerely for your kindness in writing to me, and for [your] very interesting letter. Your fact has surprised me greatly, and has alarmed me not a little, for if I am in error about Acropera I may be in error about Catasetum. Yet when I call to mind the state of the placentae in A. luteola, I am astonished that they should produce ovules. You will see in my book that I state that I did not look at the ovarium of A. Loddigesii. Would you have the kindness to send me word which end of the ovarium is meant by apex (that nearest the flower?), for I must try and get this species from Kew and look at its ovarium. I shall be extremely curious to hear whether the fruit, which is now maturing, produces a large number of good and plump seed; perhaps you may have seen the ripe capsules of other Vandeae, and may be able to form some conjecture what it ought to produce. In the young, unfertilised ovaria of many Vandeae there seemed an infinitude of ovules. In desperation it occurs to me as just possible, as almost everything in nature goes by gradation, that a properly male flower might occasionally produce a few seeds, in the same manner as female plants sometimes produce a little pollen. All your remarks seem to me excellent and very interesting, and I again thank you for your kindness in writing to me. I am pleased to observe that my description of the structure of Acropera seems to agree pretty well with what you have observed. Does it not strike you as very difficult to understand how insects remove the pollinia and carry them to the stigmas? Your suggestion that the mouth of the stigmatic cavity may become charged with viscid matter and thus secure the pollinia, and that the pollen-tubes may then protrude, seems very ingenious and new to me; but it would be very anomalous in orchids, i.e.