Requests that DO examine enclosed microscope slides of Acropera ovules, to confirm CD's opinion that females are non-functional.
Can DO comment on disagreement between Robert Brown and John Lindley over the number of Acropera carpels?
O. Heer's Atlantis theory vs CD's hypothesis of a migration north during warm periods.
Down Bromley Kent
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.— 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.
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. 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; & 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?
I am glad to hear from Hooker that you are going to consider O. Heer: his Atlantis-map seems to me very wild.— 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.—
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
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.—
- f1 3333.f1The year is given by the reference to CD's work on the ovules of Acropera. His observations were included in Orchids, which was published in May 1862.
- f2 3333.f2See letter to J. D. Hooker, 25 November .
- f3 3333.f3CD had been investigating the pollination mechanism of Acropera since October (see letters to J. D. Hooker, 15 October , 18 October , and 27 October ). In Orchids he related how he `had given up the whole case as inexplicable' when it occurred to him that `although no instance of the separation of the two sexes was known in Orchids, yet that Acropera might be a male plant.' (Orchids, p. 206). He further suggested that several species of Catasetum were male forms and that Monachanthus, Myanthus, and Cycnoches exhibited a variety of sexual forms (ibid., pp. 237--47, 269).
- f4 3333.f4CD described the results of his microscopic examination of the ovules of Acropera, and his reasons for concluding that the flower was a male form, in Orchids, pp. 207--10.
- f5 3333.f5See Lindley 1853, p. 174, Link 1849, and Brown 1831.
- f6 3333.f6The letter from Oliver has not been found; see, however, the letters to J. D. Hooker, 25 November , and to Daniel Oliver, 7 December .
- f7 3333.f7To account for the European character of the flora of Madeira and for the presence of American forms, Oswald Heer had proposed that Madeira, the Canaries, Porto Santo, and the Azores were the remnants of a sunken land-mass, or `Atlantis', that in the Tertiary period had been connected by a land-bridge to America and Europe (Heer 1857). CD had long been critical of attempts to explain geographical distribution by postulating former land-bridges (see especially Correspondence vol. 6, letters to Charles Lyell, 16 [June 1856] and 25 June ). Oliver's critique of Heer's work was published in the Natural History Review (Oliver 1862a).
- f8 3333.f8CD postulated that during a pre-glacial warm period, northern temperate forms lived at latitudes further north and nearer to the pole than at present, and were able to migrate freely across the almost continuous land between western Europe and eastern America via Siberia (Origin, pp. 369--70; see also Correspondence vol. 7, letter to Asa Gray, 11 August ).