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Fertilisation of Cypripediums.—As the sexes of Orchids form a subject of considerable interest, I beg to forward you the accompanying specimens of Cypripedium insigne.¹ Of this I have several plants, all however originally derived from the same piece, but in spite of numerous attempts, I have uniformly failed to fertilise the flowers. The seed-vessel swells and the flower fades as usual, but no seed is produced. It appears to me that my plant produces a male flower only, and is not hermaphrodite. Have any others of your correspondents made a similar observation? I enclose a flower of Cypripedium insigne and two barren seed-vessels, to which the pollen of C. barbatum and C. venustum was applied this year. To prove that the pollen masses of the plant in question are good, I send also a seed-vessel of C. barbatum, fertilised with the pollen of one of the same flowers of C. insigne, and which is full of seeds. A. D. B.²
[The specimens forwarded appeared on examination to be perfectly formed as regards their stamens and pistils, but perfectly destitute of ovules. On forwarding them to Mr. Darwin, that gentleman kindly favoured us with the following remarks. EDS.:—
From the remarkable fact lately ascertained by Dr. Hildebrand,³ that with many Orchids the ovules do not become developed until many weeks or even months have elapsed after the pollen-tubes have penetrated the stigma, it is not a little difficult to ascertain whether any Orchis is exclusively a male plant, that is, whether the female organs have aborted. Of course there is no difficulty in ascertaining the rudimentary condition of the pollen, and so ascertaining that a plant is a female. The explanation of the sterility of the seed-capsules in the Cypripediums sent to me I have little doubt lies in the circumstance of their having been fertilised by pollen taken from the same plant or seedling. I now know of a long series of cases in which various Orchids are absolutely sterile when impregnated by their own pollen (proved, however, to be in itself effective), but which can be easily impregnated by pollen taken from other individuals of the same species, or from distinct species. These facts strike me as most remarkable under a physiological point of view, and they point to the necessity of an occasional or regular union between distinct individuals of the same species. Ch. Darwin.]

¹ Lady's-slipper orchid. See Correspondence vol. 15, pp. 182-4.

² A.D.B. has not been identified.

³ Friedrich Hildebrand (1835-1915), German botanist.