Dear Sir.

The well known interest which you take in the fertilisation of Orchids, has induced me to forward you the enclosed copy of a paper contributed by me to the New Zealand Institute; in which I have attempted to describe the singular contrivances in our species of Pterostylis.¹ I thought, too, that the regret you express, in your book on the subject, at not being able to examine any species with an irritable labellum,² might be advanced as an additional excuse for the liberty I have taken in sending you an account of a mode of fertilisation depending entirely on this irritability.

My observations, and the experiments I have made, seem to me to fully warrant the conclusions I have arrived at in my paper. I should much like, however, if it would not be trespassing too much on your good nature, to have your opinion on the subject.³ Do you not think that the Australian Genus Calæna, in which the labellum is even more irritable than in Pterostylis, is likely to be fertilised in an analogous manner? I have not seen recent specimens, but the plant is so nearly allied to Pterostylis that this view seems highly probable

If it would be of any use to you I should be happy to forward you specimens of our Orchidea or to procure you any information in my power.

I remain | Yours very faithfully | Thos. F. Cheeseman

Charles Darwin Esq F.R.S....