[page] 237

FERTILISATION OF ORCHIDS.

HAD Mr. Anderson¹ asked me two days ago for any facts illustrative of his case of unopened flowers of Cattleya crispa and Dendrobium cretaceum producing seed-capsules, I could have given no sort of information; nor can I now explain the fact. By an odd coincidence, yesterday I received a very interesting letter from Dr. Hermann Cruger,² the Director of the Botanic Garden at Trinidad, who informs me that certain native species, and native species alone, of Cattleya, Epidendrum, and Schomburghkia, "are hardly ever known to open their flowers, but which nearly always set fruit." In answer to Dr. Cruger, I have asked him to look at the seed or send me some, and inform me whether it appears good.

Will Mr. Anderson have the kindness to send me a few seeds produced by his unopened flowers?

I further asked Dr. Cruger whether these Orchids in their native haunts never open their flowers. I can hardly believe that this can be the case, seeing how manifestly adapted the structure of their organs of fructification is to the action of insects. But it is known that several plants, such as Violets, Campanulas, Oxalis, &c., produce two kinds of flowers: one sort adapted for self-fertilisation, and the other sort for fertilisation by insect agency or other means. In some cases the two kinds of flowers differ very little in structure; and it occurs to me as possible that something of this kind may occur with Orchids.

Dr. Cruger further informs me that with certain Orchids, as in those which do not open their flowers, the pollen-masses after a time become pulpy; and though remaining still in situ, emit their pollen-tubes, which reach the stigma, and thus cause fertilisation.

An excellent observer, Mr. J. Scott,³ of the Royal Botanic Gardens of Edinburgh, will, I am sure, permit me to state that he has been making similar observations, and has seen the pollen-tubes emitted from the pollen-masses whilst still in their proper positions.

These facts were all unknown to me when I published my small work on the Fertilisation of Orchids; but I ought, perhaps, to have anticipated their occurrence, for I saw the pollen-tubes emitted from the pollen within the anthers in the Bird's-nest Orchid, and likewise in monstrous flowers of the Man Orchis. This latter fact seems related to Mr. Anderson's remark, that flowers of an imperfect character, wanting a petal or sepal, had a great tendency to produce seed-capsules.⁴

These curious observations by Dr. Cruger, Mr. Anderson, and Mr. Scott, convince me that I have in my work underrated the power of tropical Orchids occasionally to produce seed without the aid of insects; but I am not shaken in my belief that their structure is mainly related to insect agency. With most British Orchids this conclusion may be looked on as established.

I will only add that since the publication of my work, a number of persons have set seed-capsules with various tropical Orchids.

CHARLES DARWIN, Down, Bromley, Kent.

¹ James Anderson (1831/2-1899), Scottish gardener and orchid specialist. Darwin refers to Anderson 1863.

² Hermann Crüger (1818-1864), German pharmacist and botanist. See Correspondence vol. 11.

³ John Scott (1836-1880), Scottish botanist.

⁴ Anderson 1863, p. 207.