Volume Ii Part 28 (2/2)

1875, Volume I., page 184, Darwin was the first to make substantial additions to the conclusions deducible from the course of the vessels in relation to the problem of the morphology of these plants. Eichler gives Darwin's diagram side by side with that of Van Tieghem without attempting to decide between the differences in detail by which they are characterised.)

I find that the great Bauer does not draw very correctly! (602/3. F.

Bauer, whom Pritzel calls ”der grosste Pflanzenmaler.” The reference is to his ”Ill.u.s.trations of Orchidaceous Plants, with Notes and Prefatory Remarks by John Lindley,” London, 1830-38, Folio. See ”Fertilisation of Orchids,” Edition II., page 82.) And, good Heavens, what a jumble he makes on functions.

LETTER 603. TO J.D. HOOKER. Down, October 22nd. [1861].

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.

I never saw the very curious flower of Canna; I should say the pollen was deposited where it is to prevent inevitable self-fertilisation.

You have no time to try the smallest experiment, else it would 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 the tube formed by pistil, stamen and ”nectarblatt” secretes (I presume internally) much nectar. Thanks for sending me the curious flower.

Now I want much some wisdom; though I must write at considerable length, your answer may be very brief.

(FIGURE 8.--FLORAL DIAGRAM OF AN ORCHID. The ”missing bundle” could not be found in some species.)

In R. Brown's admirable paper in the ”Linnean Transacts.” (603/4. Volume XVI., page 685.) he suggests (and Lindley cautiously agrees) that the flower of orchids consists of five whorls, the inner whorl of the two whorls of anthers being all rudimentary, and when the labellum presents ridges, two or three of the anthers of both whorls [are] combined with it. 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, and I have succeeded well. Look at my diagram [Figure 8] (which please return, for I am transported with admiration at it), which shows the vessels which I have traced, one bundle to each of fifteen theoretical organs, and no more. 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 the lower sepal, to the side of the labellum, and 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 the rostellum. But here comes my only point of novelty: in all orchids as yet looked at (even one with so simple a labellum as Gymnadenia and Malaxis) the vessels on the two sides of the labellum are derived from the bundle which goes to the lower sepal, as in the diagram. This leads me to conclude that the 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 the orifice of the nectary it turns and runs right down it, then comes up the opposite side and runs to the apex of the labellum, whence each side of the nectary is supplied by vessels from the bundles, coming from the lower sepals.

Hence even the thin nectary is essentially, I infer, tripart.i.te; hence its tendency to bifurcation at its top. This view of the labellum always consisting of three organs (I believe four when thick, as in Mormodes, at base) seems to me to explain its great size and tripart.i.te form, compared with the other petals. Certainly, if I may trust the 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 the subject: the destiny of the whole human race is as nothing to the course of vessels of orchids...

What plant has the most complex single stigma and 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.

To-morrow 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.

According to the vessels, an orchid flower consists of three sepals and two petals free; and of a compound organ (its labellum), consisting of one petal and of two (or three) modified anthers; and of a second compound body consisting of three pistils, one normal anther, and two modified anthers often forming the sides of the clinandrum.

LETTER 604. TO JOHN LINDLEY.

(604/1. It was in the autumn of 1861 that Darwin made up his mind to publish his Orchid work as a book, rather than as a paper in the Linnean Society's ”Journal.” (604/2. See ”Life and Letters,” III., page 266.) The following letter shows that the new arrangement served as an incitement to fresh work.)

Down, October 25th [1861?]

Mr. James Veitch has been most generous. I did not know that you had spoken to him. If you see him pray say I am truly grateful; I dare not write to a live Bishop or a Lady, but if I knew the address of ”Rucker”?

and might use your name as introduction, I might write. I am half mad on the subject. Hooker has sent me many exotics, but I stopped him, for I thought I should make a fool of myself; but since I have determined to publish I much regret it.

(FIGURE 9.--HABENARIA CHLORANTHA (Longitudinal course of bundles).)

(605/1. The three upper curved outlines, two of which pa.s.sing through the words ”upper sepal,” ”upper petal,” ”lower sepal,” were in red in the original; for explanation see text.)

LETTER 605. TO J.D. HOOKER.

(605/2. The following letter is of interest because it relates to one of the two chief difficulties Darwin met with in working out the morphology of the orchid flower. In the orchid book (605/3. Edition I., page 303.) he wrote, ”This anomaly [in Habenaria] is so far of importance, as it throws some doubt on the view which I have taken of the labellum being always an organ compounded of one petal and two petaloid stamens.” That is to say, it leaves it open for a critic to a.s.sert that the vessels which enter the sides of the labellum are lateral vessels of the petal and do not necessarily represent petaloid stamens. In the sequel he gives a satisfactory answer to the supposed objector.)

Down, November 10th, [1861].

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