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Darwin Correspondence Project

To J. D. Hooker   27 October [1861]

Down Bromley Kent

Oct 27.

My dear Hooker

Acropera is a beast—stigma does not open; everything seems contrived that it shall not be anyhow fertilised. There is something very odd about it, which could only be made out by incessant watching on several individual plants.1

I never saw the very curious flower of Canna; I shd say pollen was deposited where it is, to prevent inevitable self-fertilisation: you have no time to try smallest experiment, else it wd. be worth while to put pollen on some stigmas, (supposing that it does not seed freely with you).— Anyhow insects would probably carry pollen from flower to flower, for Kurr states that tube formed by pistil stamen & “nektar-blatt” secretes (I presume internally) much nectar;2 thanks for sending me this curious flower.

Now I want much some wisdom; though I must write at considerable length, your answer may be very brief. (You did me a wonderful good turn in telling me to trace down the vessels in Malaxis.—)3 In R. Brown’s admirable paper in Linn. Transacts,4 he suggests (& Lindley cautiously agrees) that flower of Orchids consists of 5 whorls, the inner whorl of the two whorls of anthers being all rudimentary, & when the Labellum presents ridges, 2 or 3 of the anthers of both whorls being combined with it.5 In the ovarium there are six bundles of vessels. R. Brown judged by transverse sections. It occurred to me after what you said to trace the vessels longitudinally & I have succeeded well.6

Look at my diagram (which please return for I am transported with admiration at it), which shows the vessels which I have traced, one bundle to each of 15 theoretical organs & no more.7 You will see the result is nothing new, but it seems to confirm strongly R. Brown, for I have succeeded (perhaps he did, but he does not say so) in tracing the vessels belonging to each organ in front of each other to the same bundle in the ovarium: thus, the vessels going to lower sepal, to side of Labellum, & to one stigma (when there are two) all distinctly branch from one ovarian bundle. So in other cases, but I have not completely traced (only seen) that going to Rostellum.— But here comes my only point of novelty; in all orchids, as yet looked at, (even one with so simple a labellum as in Gymnadenia & Malaxis) the vessels on the two sides of the labellum are derived from the bundle which goes to lower sepal, as in Diagram. This leads me to conclude that Labellum is always a compound organ. Now I want to know, whether it is conceivable that the vessels coming from one main bundle should penetrate an organ, (the labellum) which receives its vessels from another main bundle? does it not imply that all that part of the labellum which is supplied by vessels coming from a lateral bundle must be part of a primordially distinct organ, however closely the two may have become united? It is curious in Gymnadenia to trace the middle anterior bundle in the ovarium, when it comes to orifice of nectary it turns & runs right down it, then comes up the opposite side & runs to apex of Labellum, whereas each side of nectary is supplied by vessels coming from the bundles coming from the lower sepals: hence even the thin nectary is essentially, I infer, tripartite; hence its tendency to bifurcation at its tip. This view of the Labellum always consisting of 3 organs (I believe 4, when thick as in Mormodes at base) seems to me to explain its great size; & tripartite form, compared with the other petals. Certainly if I may trust vessels, the simple Labellum of Gymnadenia consists of three organs soldered together.—

Forgive me for writing at such length; a very brief answer will suffice.

I am desperately interested in subject; the destiny of whole human race is as nothing to the course of vessels of Orchids.—

Your insane friend | C. Darwin

What plant has most complex single stigma & pistil: the most complex, I, in my ignorance, can think of is in Iris: I want to know whether anything beats in modification the rostellum of Catasetum.8 Tomorrow I mean to be at Catasetum— Hurrah. What species is it? it is wonderfully different from that which Veitch sent me—which was C. saccatum: a gardener here thinks it is Cat. globigerum?9 According to the vessels an Orchid-flower consists of 3 sepals & 2 petals free; & of a compound organ (the labellum) consisting of one petal & of 2 (or 3) modified anthers; & of a second compound body consisting of 3 pistils, one normal anther & 2 modified anthers often forming the sides of the clinandrum.—10

Footnotes

See letters to J. D. Hooker, 15 [October 1861] and 18 October [1861].
Kurr 1833, p. 26. Canna is briefly mentioned in Orchids in the discussion of the pollen-masses of orchids. A member of a family allied to orchids, Canna is fertilised, according to CD, by its pollen being ‘deposited on the pistil, close beneath the stigma’ (Orchids, p. 324).
Hooker’s letter has not been found, but see the letters to J. D. Hooker, 4 October [1861] and 13 October [1861].
Brown 1831, pp. 696–701. There is a copy of the paper in the Darwin Pamphlet Collection–CUL. Brown published a preliminary description of the structure of orchid flowers in Brown 1810, 1: 310.
Lindley 1853, pp. 183–3a. John Lindley illustrated his description with a diagram that CD modified for inclusion in Orchids (see Orchids, p. 292).
See letters to J. D. Hooker, 4 October [1861] and 6–7 October [1861]. In Orchids, pp. 290–1, CD explained the importance of the spiral vessels in making out the homologies of orchids: As spiral vessels are developed at a very early period of growth, which always gives much value to an organ in making out homologies; and as they are apparently of high functional importance, … it appeared to me, guided also by the advice of Dr. Hooker, to be worth while to trace upwards all the spiral vessels from the six groups surrounding the ovarium.
The diagram has not been found. The one associated with this letter (dated 22 October [1861] by Francis Darwin) in ML 2: 274 was probably enclosed with the letter to J. D. Hooker, 8 November [1861]. The lost diagram probably resembled that included in the letter to J. D. Hooker, 10 November [1861].
CD awarded Catasetum, with its ‘wonderfully modified’ sensitive rostellum, ‘the palm of victory’ for perhaps being the ‘highest’ form of orchid (see Orchids, pp. 333–5).
In Orchids, p. 214 n., CD thanked James Veitch, the Chelsea nurseryman, for supplying him with his first specimen of Catasetum saccatum. The gardener CD refers to may be Mr Horwood, the gardener of CD’s neighbour George Turnbull. CD thanked Horwood in Orchids, p. 158 n., for helping him with some of his observations. C. globiflorum is not discussed in Orchids.
See letter to J. D. Hooker, 10 November [1861], and Orchids, pp. 291–4.

Summary

Acropera anatomy puzzling. Malaxis anatomy deciphered.

Letter details

Letter no.
DCP-LETT-3301
From
Charles Robert Darwin
To
Joseph Dalton Hooker
Sent from
Down
Source of text
DAR 115: 122
Physical description
8pp †

Please cite as

Darwin Correspondence Project, “Letter no. 3301,” accessed on 19 April 2019, http://www.darwinproject.ac.uk/DCP-LETT-3301

Also published in The Correspondence of Charles Darwin, vol. 9

letter