My dear Sir.

As I have lately given Hooker such a frightful amount of trouble & as you have looked at ovules of male Lychnis, will you be so kind, (the next time you have your compound microscope out) as to look at the ovules of Acropera, (sent on glass slides by this post, & to be thrown away when looked at.) which I found, after writing to Hooker lower down in the ovarium.—² Please first look at ovules of Maxillaria & Orchis, which resemble those of all the several orchids, (including ovaria of buds) which I have examined. Now see what a vast difference the ovules, (or rather mere empty membranous fringes to the placentæ) of Acropera present. These fringes positively lie on the same ridges or placentæ which carry the true pulpy ovules in all other orchids.— You will see them also in a transverse section.— I have examined 6 specimens of Acropera; & all the ovules on whole length of the 3 placentæ were in this condition. Why I want you so much to look at these ovules & give me your opinion is that I have never before looked at an ovule; and I have reason to believe that if I can trust these observations, I shall make out sexes of Catasetum, Myanthus &c.— Though I know nothing about ovules, the difference is most conspicuous between the placentæ of Acropera & of all (except Catasetum) other orchids.³

Besides this difference in the ovules, the stigmatic chamber of Acropera is so small that pollen-masses can hardly be forced in; the surface is but little viscous, & the stigmatic utriculi are very different from those of every other orchid except Catasetum in being empty.— From these several reasons I cannot avoid belief that the Acropera flowers of two species which I have examined are males.⁴ Will you inform me whether all the several flowers of Acropera luteola sent me by Hooker came from same plant??

One other point in the ovaria of Acropera has surprised me; but unless you have carefully attended to orchids, you will perhaps not be able to express an opinion: Lindley & Link say ovarium consists of 6 carpels Brown says of three;⁵ & that three of the divisions have no homological signification. Now to my surprise I see three irregular double rows of hyaline projections, running parallel to the ovules, & belonging to the three divisions of the ovarium, which do not carry ovules: you will see a few in the transverse sections & on the dissected longitudinal fragments. What can they be? it seems to me to favour Lindley’s & Link’s view.— According to Brown they lie on the midribs of his 3 carpellary leaves: according to Lindley, they would be, I suppose, representatives of ovules.

Pray forgive my writing at such length & believe me | Yours very sincerely | C. Darwin

Is it not a rather interesting fact that you have observed in Lychnis viz ovules in the male plant?⁶

I am glad to hear from Hooker that you are going to consider O. Heer: his Atlantis-map seems to me very wild.—⁷ The view, which I give in Origin of migration by north during old warmer period seems to me much simpler & agrees better with geological facts.—⁸

P.S. I should have said that ovules of the Orchis have been in spirits: ovules of Maxillaria would have been equally plain & opake had they been in spirits; spirits make no difference to the rudimentary ovules of Acropera.— I sh^d. have imagined that the rudimentary condition of ovules & stigmatic utriculi of Acropera might have been due to culture or bad conditions, had I found any other orchids in this condition; & had not solid edges of stigmatic chamber not been so much contracted.

With respect to 6 divisions of ovarium of Orchis, are there any Monocots. with 6 carpels & only 3 pistils? I suppose not, otherwise Brown would not so have objected to Lindley’s view.—