More Letters of Charles Darwin Volume II

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Let me have a line about poor Henslow pretty soon.

(599/2. In a letter of May 18th, 1861, Darwin wrote again:--)

By the way, thanks about Beaton. I have now read more of his writings, and
one answer to me in "Cottage Gardener." I can plainly see that he is not
to be trusted. He does not well know his own subject of crossing.

LETTER 600. TO J.D. HOOKER.

(600/1. Part of this letter has been published in "Life and Letters,"
III., page 265.)

2, Hesketh Crescent, Torquay [1861].

...The beauty of the adaptation of parts seems to me unparalleled. I
should think or guess [that] waxy pollen was most differentiated. In
Cypripedium, which seems least modified, and a much exterminated group, the
grains are single. In all others, as far as I have seen, they are in
packets of four; and these packets cohere into many wedge-formed masses in
Orchis, into eight, four, and finally two. It seems curious that a flower
should exist which could, at most, fertilise only two other flowers, seeing
how abundant pollen generally is; this fact I look at as explaining the
perfection of the contrivance by which the pollen, so important from its
fewness, is carried from flower to flower. By the way, Cephalanthera has
single pollen-grains, but this seems to be a case of degradation, for the
rostellum is utterly aborted. Oddly, the columns of pollen are here kept
in place by very early penetration of pollen-tubes into the edge of the
stigma; nevertheless, it receives more pollen by insect agency. Epithecia
[Dichaea] has done me one good little turn. I often speculated how the
caudicle of Orchis had been formed. (600/2. The gradation here suggested
is thoroughly worked out in the "Fertilisation of Orchids," Edition I.,
page 323, Edition II., page 257.) I had noticed slight clouds in the
substance half way down; I have now dissected them out, and I find they are
pollen-grains fairly embedded and useless. If you suppose the pollen-
grains to abort in the lower half of the pollinia of Epipactis, but the
parallel elastic threads to remain and cohere, you have the caudicle of
Orchis, and can understand the few embedded and functionless pollen-grains.
I must not look at any more exotic orchids: hearty thanks for your offer.
But if you would make one single observation for me on Cypripedium, I
should be glad. Asa Gray writes to me that the outside of the pollen-
masses is sticky in this genus; I find that the whole mass consists of
pollen-grains immersed in a sticky brownish thick fluid. You could tell by
a mere lens and penknife. If it is, as I find it, pollen could not get on
the stigma without insect aid. Cypripedium confounds me much. I
conjecture that drops of nectar are secreted by the surface of the labellum
beneath the anthers and in front of the stigma, and that the shield over
the anthers and the form of labellum is to compel insects to insert their
proboscis all round both organs. (600/3. This view was afterwards given
up.) It would be troublesome for you to look at this, as it is always
bothersome to catch the nectar secreting, and the cup of the labellum gets
filled with water by gardener's watering.

I have examined Listera ovata, cordata, and Neottia nidus avis: the pollen
is uniform; I suspect you must have seen some observation founded on a
mistake from the penetration and hardening of sticky fluid from the
rostellum, which does penetrate the pollen a little.

It is mere virtue which makes me not wish to examine more orchids; for I
like it far better than writing about varieties of cocks and hens and
ducks. Nevertheless, I have just been looking at Lindley's list in the
"Vegetable Kingdom," and I cannot resist one or two of his great division
of Arethuseae, which includes Vanilla. And as I know so well the Ophreae,
I should like (God forgive me) any one of the Satyriadae, Disidae and
Corycidae.

I fear my long lucubrations will have wearied you, but it has amused me to
write, so forgive me.

LETTER 601. TO J.D. HOOKER.

(601/1. Part of the following letter is published in the "Life and
Letters," the remainder, with the omission of part bearing on the Glen Roy
problem, is now given as an example of the varied botanical assistance
Darwin received from Sir Joseph Hooker. For the part relating to Verbascum
see the "Variation of Animals and Plants," Edition II., 1875, Volume II.,
page 83. The point is that the white and yellow flowered plants which
occur in two species of Verbascum are undoubted varieties, yet "the
sterility which results from the crossing of the differently coloured
varieties of the same species is fully as great as that which occurs in
many cases when distinct species are crossed."

The sterility of the long-styled form (B) of Linum grandiflorum, with its
own pollen is described in "Forms of Flowers," Edition II., page 87: his
conclusions on the short-styled form (A) differ from those in the present
letter.)

September 28th [1861].

I am going to beg for help, and I will explain why I want it.

You offer Cypripedium; I should be very glad of a specimen, and of any
good-sized Vandeae, or indeed any orchids, for this reason: I never
thought of publishing separately, and therefore did not keep specimens in
spirits, and now I should be very glad of a few woodcuts to illustrate my
few remarks on exotic orchids. If you can send me any, send them by post
in a tin canister on middle of day of Saturday, October 5th, for Sowerby
will be here.

Secondly: Have you any white and yellow varieties of Verbascum which you
could give me, or propagate for me, or LEND me for a year? I have resolved
to try Gartner's wonderful and repeated statement, that pollen of white and
yellow varieties, whether used on the varieties or on DISTINCT species, has
different potency. I do not think any experiment can be more important on
the origin of species; for if he is correct we certainly have what Huxley
calls new physiological species arising. I should require several species
of Verbascum besides the white and yellow varieties of the same species.
It will be tiresome work, but if I can anyhow get the plants, it shall be
tried.

Thirdly: Can you give me seeds of any Rubiaceae of the sub-order
Cinchoneae, as Spermacoce, Diodia, Mitchella, Oldenlandia? Asa Gray says
they present two forms like Primula. I am sure that this subject is well
worth working out. I have just almost proved a very curious case in Linum
grandiflorum which presents two forms, A and B. Pollen of A is perfectly
fertile on stigma of A. But pollen of B is absolutely barren on its own
stigma; you might as well put so much flour on it. It astounded me to see
the stigmas of B purple with its own pollen; and then put a few grains of
similar-looking pollen of A on them, and the germen immediately and always
swelled; those not thus treated never swelling.

Fourthly: Can you give me any very hairy Saxifraga (for their functions)
[i.e. the functions of the hairs]?

I send you a resume of my requests, to save you trouble. Nor would I ask
for so much aid if I did not think all these points well worth trying to
investigate.

My dear old friend, a letter from you always does me a world of good. And,
the Lord have mercy on me, what a return I make.

LETTER 602. TO J.D. HOOKER.
Down, October 4th [1861].

Will you have the kindness to read the enclosed, and look at the diagram.
Six words will answer my question. It is not an important point, but there
is to me an irresistible charm in trying to make out homologies. (602/1.
In 1880 he wrote to Mr. Bentham: "It was very kind of you to write to me
about the Orchideae, for it has pleased me to an extreme degree that I
could have been of the least use to you about the nature of the parts."--
"Life and Letters," III., page 264.) You know the membranous cup or
clinandrum, in many orchids, behind the stigma and rostellum: it is formed
of a membrane which unites the filament of the normal dorsal anther with
the edges of the pistil. The clinandrum is largely developed in Malaxis,
and is of considerable importance in retaining the pollinia, which as soon
as the flower opens are quite loose.

The appearance and similarity of the tissues, etc., at once gives suspicion
that the lateral membranes of the clinandrum are the two other and
rudimentary anthers, which in Orchis and Cephalanthera, etc., exist as mere
papillae, here developed and utilised.

Now for my question. Exactly in the middle of the filament of the normal
anther, and exactly in the middle of the lateral membrane of the
clinandrum, and running up to the same height, are quite similar bundles of
spiral vessels; ending upwards almost suddenly. Now is not this structure
a good argument that I interpret the homologies of the sides of clinandrum
rightly? (602/2. Though Robert Brown made use of the spiral vessels of
orchids, yet according to Eichler, "Bluthendiagramme," 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 "Illustrations 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, tripartite; 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
tripartite 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 passing 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 assert 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].

For the love of God help me. I believe all my work (about a fortnight) is
useless. Look at this accursed diagram (Figure 9) of the butterfly-orchis
[Habenaria], which I examined after writing to you yesterday, when I
thought all my work done. Some of the ducts of the upper sepal (605/4.
These would be described by modern morphologists as lower, not upper,
sepals, etc. Darwin was aware that he used these terms incorrectly.) and
upper petal run to the wrong bundles on the column. I have seen no such
case.

This case apparently shows that not the least reliance can be placed on the
course of ducts. I am sure of my facts.

There is great adhesion and extreme displacement of parts where the organs
spring from the top of the ovarium. Asa Gray says ducts are very early
developed, and it seems to me wonderful that they should pursue this
course. It may be said that the lateral ducts in the labellum running into
the antero-lateral ovarian bundle is no argument that the labellum consists
of three organs blended together.

In desperation (and from the curious way the base of upper petals are
soldered at basal edges) I fancied the real form of upper sepal, upper
petal and lower sepal might be as represented by red lines, and that there
had been an incredible amount of splitting of sepals and petals and
subsequent fusion.

This seems a monstrous notion, but I have just looked at Bauer's drawing of
allied Bonatea, and there is a degree of lobing of petals and sepals which
would account for anything.

Now could you spare me a dry flower out of your Herbarium of Bonatea
speciosa (605/5. See "Fertilisation of Orchids," Edition I., page 304
(note), where the resemblances between the anomalous vessels of Bonatea and
Habenaria are described. On November 14th, 1861, he wrote to Sir Joseph:
"You are a true friend in need. I can hardly bear to let the Bonatea soak
long enough."), that I might soak and look for ducts. If I cannot explain
the case of Habenaria all my work is smashed. I was a fool ever to touch
orchids.

LETTER 606. TO J.D. HOOKER.
Down, November 17th [1861].

What two very interesting and useful letters you have sent me. You rather
astound me with respect to value of grounds of generalisation in the
morphology of plants. It reminds me that years ago I sent you a grass to
name, and your answer was, "It is certainly Festuca (so-and-so), but it
agrees as badly with the description as most plants do." I have often
laughed over this answer of a great botanist...Lindley, from whom I asked
for an orchid with a simple labellum, has most kindly sent me a lot of what
he marks "rare" and "rarissima" of peloric orchids, etc., but as they are
dried I know not whether they will be of use. He has been most kind, and
has suggested my writing to Lady D. Nevill, who has responded in a
wonderfully kind manner, and has sent a lot of treasures. But I must stop;
otherwise, by Jove, I shall be transformed into a botanist. I wish I had
been one; this morphology is surprisingly interesting. Looking to your
note, I may add that certainly the fifteen alternating bundles of spiral
vessels (mingled with odd beadlike vessels in some cases) are present in
many orchids. The inner whorl of anther ducts are oftenest aborted. I
must keep clear of Apostasia, though I have cast many a longing look at it
in Bauer. (606/1. Apostasia has two fertile anthers like Cypripedium. It
is placed by Engler and Prantl in the Apostasieae or Apostasiinae, among
the Orchideae, by others in a distinct but closely allied group.)

I hope I may be well enough to read my own paper on Thursday, but I have
been very seedy lately. (606/2. "On the two Forms, or Dimorphic
Condition, in the Species of the Genus Primula," "Linn. Soc. Journ." 1862.
He did read the paper, but it cost him the next day in bed. "Life and
Letters," III., page 299.) I see there is a paper at the Royal on the same
night, which will more concern you, on fossil plants of Bovey (606/3.
Oswald Heer, "The Fossil Flora of Bovey Tracey," "Phil. Trans. R. Soc."
1862, page 1039.), so that I suppose I shall not have you; but you must
read my paper when published, as I shall very much like to hear what you
think. It seems to me a large field for experiment. I shall make use of
my Orchid little volume in illustrating modification of species doctrine,
but I keep very, very doubtful whether I am not doing a foolish action in
publishing. How I wish you would keep to your old intention and write a
book on plants. (606/4. Possibly a book similar to that described in
Letter 696.)

LETTER 607. TO G. BENTHAM.
Down, November 26th [1861].

Our notes have crossed on the road. I know it is an honour to have a paper
in the "Transactions," and I am much obliged to you for proposing it, but I
should greatly prefer to publish in the "Journal." Nor does this apply
exclusively to myself, for in old days at the Geological Society I always
protested against an abstract appearing when the paper itself might appear.
I abominate also the waste of time (and it would take me a day) in making
an abstract. If the referee on my paper should recommend it to appear in
the "Transactions," will you be so kind as to lay my earnest request before
the Council that it may be permitted to appear in the "Journal?"

You must be very busy with your change of residence; but when you are
settled and have some leisure, perhaps you will be so kind as to give me
some cases of dimorphism, like that of Primula. Should you object to my
adding them to those given me by A. Gray? By the way, I heard from A. Gray
this morning, and he gives me two very curious cases in Boragineae.

LETTER 608. TO JOHN LINDLEY.

(608/1. In the following fragment occurs the earliest mention of Darwin's
work on the three sexual forms of Catasetum tridentatum. Sir R. Schomburgk
(608/2. "Trans. Linn. Soc." XVII., page 522.) described Catasetum
tridentatum, Monacanthus viridis and Myanthus barbatus occurring on a
single plant, but it remained for Darwin to make out that they are the
male, female and hermaphrodite forms of a single species. (608/3.
"Fertilisation of Orchids," Edition I., page 236; Edition II., page 196.)

With regard to the species of Acropera (Gongora) (608/4. Acropera
Loddigesii = Gongora galeata: A. luteola = G. fusca ("Index Kewensis").)
he was wrong in his surmise. The apparent sterility seems to be explicable
by Hildebrand's discovery (608/5. "Bot. Zeitung," 1863 and 1865.) that in
some orchids the ovules are not developed until pollinisation has occurred.
(608/6. "Fertilisation of Orchids," Edition II., page 172. See Letter
633.))

Down, December 15th [1861].

I am so nearly ready for press that I will not ask for anything more;
unless, indeed, you stumbled on Mormodes in flower. As I am writing I will
just mention that I am convinced from the rudimentary state of the ovules,
and from the state of the stigma, that the whole plant of Acropera luteola
(and I believe A. Loddigesii) is male. Have you ever seen any form from
the same countries which could be the females? Of course no answer is
expected unless you have ever observed anything to bear on this. I may add
[judging from the] state of the ovules and of the pollen [that]:--

Catasetum tridentatum is male (and never seeds, according to Schomburgk,
whom you have accidentally misquoted in the "Vegetable Kingdom").
Monacanthus viridis is female. Myanthus barbatus is the hermaphrodite form
of same species.

LETTER 609. TO J.D. HOOKER.
Down, December 18th [1861].

Thanks for your note. I have not written for a long time, for I always
fancy, busy as you are, that my letters must be a bore; though I like
writing, and always enjoy your notes. I can sympathise with you about fear
of scarlet fever: to the day of my death I shall never forget all the
sickening fear about the other children, after our poor little baby died of
it. The "Genera Plantarum" must be a tremendous work, and no doubt very
valuable (such a book, odd as it may appear, would be very useful even to
me), but I cannot help being rather sorry at the length of time it must
take, because I cannot enter on and understand your work. Will you not be
puzzled when you come to the orchids? It seems to me orchids alone would
be work for a man's lifetime; I cannot somehow feel satisfied with
Lindley's classification; the Malaxeae and Epidendreae seem to me very
artificially separated. (609/1. Pfitzer (in the "Pflanzenfamilien")
places Epidendrum in the Laeliinae-Cattleyeae, Malaxis in the Liparidinae.
He states that Bentham united the Malaxideae and Epidendreae.) Not that I
have seen enough to form an opinion worth anything.

Your African plant seems to be a vegetable Ornithorhynchus, and indeed much
more than that. (609/2. See Sir J.D. Hooker, "On Welwitschia, a new genus
of Gnetaceae." "Linn. Soc. Trans." XXIV., 1862-3.) The more I read about
plants the more I get to feel that all phanerogams seem comparable with one
class, as lepidoptera, rather than with one kingdom, as the whole insecta.
(609/3. He wrote to Hooker (December 28th, 1861): "I wrote carelessly
about the value of phanerogams; what I was thinking of was that the sub-
groups seemed to blend so much more one into another than with most classes
of animals. I suspect crustacea would show more difference in the extreme
forms than phanerogams, but, as you say, it is wild speculation. Yet it is
very strange what difficulty botanists seem to find in grouping the
families together into masses.")