More Letters of Charles Darwin Volume II

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LETTER 697. TO J.D. HOOKER.
Down, December 5th, 1868.

...Now I want to beg for assistance for the new edition of "Origin."
Nageli himself urges that plants offer many morphological differences,
which from being of no service cannot have been selected, and which he
accounts for by an innate principle of progressive development. (697/1.
Nageli's "Enstehung und Begriff der Naturhistorischen Art." An address
delivered at the public session of the Royal Academy of Sciences of Munich,
March 28th, 1865; published by the Academy. Darwin's copy is the 2nd
edition; it bears signs, in the pencilled notes on the margins, of having
been read with interest. Much of it was translated for him by a German
lady, whose version lies with the original among his pamphlets. At page 27
Nageli writes: "It is remarkable that the useful adaptations which Darwin
brings forward in the case of animals, and which may be discovered in
numbers among plants, are exclusively of a physiological kind, that they
always show the formation or transformation of an organ to a special
function. I do not know among plants a morphological modification which
can be explained on utilitarian principles." Opposite this passage Darwin
has written "a very good objection": but Nageli's sentence seems to us to
be of the nature of a truism, for it is clear that any structure whose
evolution can be believed to have come about by Natural Selection must have
a function, and the case falls into the physiological category. The
various meanings given to the term morphological makes another difficulty.
Nageli cannot use it in the sense of "structural"--in which sense it is
often applied, since that would mean that no plant structures have a
utilitarian origin. The essence of morphology (in the better and more
precise sense) is descent; thus we say that a pollen-grain is
morphologically a microspore. And this very example serves to show the
falseness of Nageli's view, since a pollen-grain is an adaptation to aerial
as opposed to aquatic fertilisation. In the 5th edition of the "Origin,"
1869, page 151, Darwin discusses Nageli's essay, confining himself to the
simpler statement that there are many structural characters in plants to
which we cannot assign uses. See Volume I., Letter 207.) I find old notes
about this difficulty; but I have hitherto slurred it over. Nageli gives
as instances the alternate and spiral arrangement of leaves, and the
arrangement of the cells in the tissues. Would you not consider as a
morphological difference the trimerous, tetramerous, etc., divisions of
flowers, the ovules being erect or suspended, their attachment being
parietal or placental, and even the shape of the seed when of no service to
the plant.

Now, I have thought, and want to show, that such differences follow in some
unexplained manner from the growth or development of plants which have
passed through a long series of adaptive changes. Anyhow, I want to show
that these differences do not support the idea of progressive development.
Cassini states that the ovaria on the circumference and centre of Compos.
flowers differ in essential characters, and so do the seeds in sculpture.
The seeds of Umbelliferae in the same relative positions are coelospermous
and orthospermous. There is a case given by Augt. St. Hilaire of an erect
and suspended ovule in the same ovarium, but perhaps this hardly bears on
the point. The summit flower, in Adoxa and rue differ from the lower
flowers. What is the difference in flowers of the rue? how is the ovarium,
especially in the rue? As Augt. St. Hilaire insists on the locularity of
the ovarium varying on the same plant in some of the Rutaceae, such
differences do not speak, as it seems to me, in favour of progressive
development. Will you turn the subject in your mind, and tell me any more
facts. Difference in structure in flowers in different parts of the same
plant seems best to show that they are the result of growth or position or
amount of nutriment.

I have got your photograph (697/2. A photograph by Mrs. Cameron.) over my
chimneypiece, and like it much; but you look down so sharp on me that I
shall never be bold enough to wriggle myself out of any contradiction.

Owen pitches into me and Lyell in grand style in the last chapter of volume
3 of "Anat. of Vertebrates." He is a cool hand. He puts words from me in
inverted commas and alters them. (697/3. The passage referred to seems to
be in Owen's "Anatomy of Vertebrata," III., pages 798, 799, note. "I
deeply regretted, therefore, to see in a 'Historical Sketch' of the
Progress of Enquiry into the origin of species, prefixed to the fourth
edition of that work (1866), that Mr. Darwin, after affirming inaccurately
and without evidence, that I admitted Natural Selection to have done
something toward that end, to wit, the 'origin of species,' proceeds to
remark: 'It is surprising that this admission should not have been made
earlier, as Prof. Owen now believes that he promulgated the theory of
Natural Selection in a passage read before the Zoological Society in
February, 1850, ("Trans." Volume IV., page 15).'" The first of the two
passages quoted by Owen from the fourth edition of the "Origin" runs: "Yet
he [Prof. Owen] at the same time admits that Natural Selection MAY [our
italics] have done something towards this end." In the sixth edition of
the "Origin," page xviii., Darwin, after referring to a correspondence in
the "London Review" between the Editor of that Journal and Owen, goes on:
"It appeared manifest to the editor, as well as to myself, that Prof. Owen
claimed to have promulgated the theory of Natural Selection before I had
done so;...but as far as it is possible to understand certain recently
published passages (Ibid. ["Anat. of Vert."], Volume III., page 798), I
have either partly or wholly again fallen into error. It is consolatory to
me that others find Prof. Owen's controversial writings as difficult to
understand and to reconcile with each other, as I do. As far as the mere
enunciation of the principle of Natural Selection is concerned, it is quite
immaterial whether or no Prof. Owen preceded me, for both of us, as shown
in this historical sketch, were long ago preceded by Dr. Wells and Mr.
Matthews.")

LETTER 698. TO J.D. HOOKER.
Down, December 29th, 1868.

Your letter is quite invaluable, for Nageli's essay (698/1. See preceding
Letter.) is so clever that it will, and indeed I know it has produced a
great effect; so that I shall devote three or four pages to an answer. I
have been particularly struck by your statements about erect and suspended
ovules. You have given me heart, and I will fight my battle better than I
should otherwise have done. I think I cannot resist throwing the
contrivances in orchids into his teeth. You say nothing about the flowers
of the rue. (698/2. For Ruta see "Origin," Edition V., page 154.) Ask
your colleagues whether they know anything about the structure of the
flower and ovarium in the uppermost flower. But don't answer on purpose.

I have gone through my long Index of "Gardeners' Chronicle," which was made
solely for my own use, and am greatly disappointed to find, as I fear,
hardly anything which will be of use to you. (698/3. For Hooker's
projected biological book, see Letter 696.) I send such as I have for the
chance of their being of use.

LETTER 699. TO J.D. HOOKER.
Down, January 16th [1869].

Your two notes and remarks are of the utmost value, and I am greatly
obliged to you for your criticism on the term. "Morphological" seems quite
just, but I do not see how I can avoid using it. I found, after writing to
you, in Vaucher about the Rue (699/1. "Plantes d'Europe," Volume I., page
559, 1841.), but from what you say I will speak more cautiously. It is the
Spanish Chesnut that varies in divergence. Seeds named Viola nana were
sent me from Calcutta by Scott. I must refer to the plants as an "Indian
species," for though they have produced hundreds of closed flowers, they
have not borne one perfect flower. (699/2. The cleistogamic flowers of
Viola are used in the discussion on Nageli's views. See "Origin," Edition
V., page 153.) You ask whether I want illustrations "of ovules differing
in position in different flowers on the same plant." If you know of such
cases, I should certainly much like to hear them. Again you speak of the
angle of leaf-divergence varying and the variations being transmitted. Was
the latter point put in in a hurry to round the sentence, or do you really
know of cases?

Whilst looking for notes on the variability of the divisions of the
ovarium, position of the ovules, aestivation, etc., I found remarks written
fifteen or twenty years ago, showing that I then supposed that characters
which were nearly uniform throughout whole groups must be of high vital
importance to the plants themselves; consequently I was greatly puzzled
how, with organisms having very different habits of life, this uniformity
could have been acquired through Natural Selection. Now, I am much
inclined to believe, in accordance with the view given towards the close of
my MS., that the near approach to uniformity in such structures depends on
their not being of vital importance, and therefore not being acted on by
Natural Selection. (699/3. This view is given in the "Origin," Edition
VI., page 372.) If you have reflected on this point, what do you think of
it? I hope that you approved of the argument deduced from the
modifications in the small closed flowers.

It is only about two years since last edition of "Origin," and I am fairly
disgusted to find how much I have to modify, and how much I ought to add;
but I have determined not to add much. Fleeming Jenkin has given me much
trouble, but has been of more real use to me than any other essay or
review. (699/4. On Fleeming Jenkin's review, "N. British Review," June,
1867, see "Life and Letters," III., page 107.)

LETTER 700. TO J.D. HOOKER.
Down [January 22nd, 1869].

Your letter is quite splenditious. I am greatly tempted, but shall, I
hope, refrain from using some of your remarks in my chapter on
Classification. It is very true what you say about unimportant characters
being so important systematically; yet it is hardly paradoxical bearing in
mind that the natural system is genetic, and that we have to discover the
genealogies anyhow. Hence such parts as organs of generation are so useful
for classification though not concerned with the manner of life. Hence use
for same purpose of rudimentary organs, etc. You cannot think what a
relief it is that you do not object to this view, for it removes PARTLY a
heavy burden from my shoulders. If I lived twenty more years and was able
to work, how I should have to modify the "Origin," and how much the views
on all points will have to be modified! Well, it is a beginning, and that
is something...

LETTER 701. TO T.H. FARRER (Lord Farrer).
Down, August 10th, 1869.

Your view seems most ingenious and probable; but ascertain in a good many
cases that the nectar is actually within the staminal tube. (701/1. It
seems that Darwin did not know that the staminal tube in the diadelphous
Leguminosae serves as a nectar-holder, and this is surprising, as Sprengel
was aware of the fact.) One can see that if there is to be a split in the
tube, the law of symmetry would lead it to be double, and so free one
stamen. Your view, if confirmed, would be extremely well worth publication
before the Linnean Society. It is to me delightful to see what appears a
mere morphological character found to be of use. It pleases me the more as
Carl Nageli has lately been pitching into me on this head. Hooker, with
whom I discussed the subject, maintained that uses would be found for lots
more structures, and cheered me by throwing my own orchids into my teeth.
(701/2. See Letters 697-700.)

All that you say about changed position of the peduncle in bud, in flower,
and in seed, is quite new to me, and reminds me of analogous cases with
tendrils. (701/3. See Vochting, "Bewegung der Bluthen und Fruchte," 1882;
also Kerner, "Pflanzenleben," Volume I., page 494, Volume II., page 121.)
This is well worth working out, and I dare say the brush of the stigma.

With respect to the hairs or filaments (about which I once spoke) within
different parts of flowers, I have a splendid Tacsonia with perfectly
pendent flowers, and there is only a microscopical vestige of the corona of
coloured filaments; whilst in most common passion-flowers the flowers stand
upright, and there is the splendid corona which apparently would catch
pollen. (701/4. Sprengel ("Entdeckte Geheimniss," page 164) imagined that
the crown of the Passion-flower served as a nectar-guide and as a platform
for insects, while other rings of filaments served to keep rain from the
nectar. F. Muller, quoted in H. Muller ("Fertilisation," page 268), looks
at the crowns of hairs, ridges in some species, etc., as gratings serving
to imprison flies which attract the fertilising humming-birds. There is,
we believe, no evidence that the corona catches pollen. See Letter 704,
note.)

On the lower side of corolla of foxglove there are some fine hairs, but
these seem of not the least use (701/5. It has been suggested that the
hairs serve as a ladder for humble bees; also that they serve to keep out
"unbidden guests.")--a mere purposeless exaggeration of down on outside--as
I conclude after watching the bees at work, and afterwards covering up some
plants; for the protected flowers rarely set any seed, so that the hairy
lower part of corolla does not come into contact with stigma, as some
Frenchman says occurs with some other plants, as Viola odorata and I think
Iris.

I heartily wish I could accept your kind invitation, for I am not by nature
a savage, but it is impossible. Forgive my dreadful handwriting, none of
my womenkind are about to act as amanuensis.

LETTER 702. TO WILLIAM C. TAIT.

(702/1. Mr. Tait, to whom the following letter is addressed, was resident
in Portugal. His kindness in sending plants of Drosophyllum lusitanicum is
acknowledged in "Insectivorous Plants.")

Down, March 12th, 1869.

I have received your two letters of March 2nd and 5th, and I really do not
know how to thank you enough for your extraordinary kindness and energy. I
am glad to hear that the inhabitants notice the power of the Drosophyllum
to catch flies, for this is the subject of my studies. (702/2. The
natives are said to hang up plants of Drosophyllum in their cottages to act
as fly-papers ("Insectivorous Plants," page 332).) I have observed during
several years the manner in which this is effected, and the results
produced in several species of Drosera, and in the wonderful American
Dionoea, the leaves of which catch insects just like a steel rat-trap.
Hence I was most anxious to learn how the Drosophyllum would act, so that
the Director of the Royal Gardens at Kew wrote some years ago to Portugal
to obtain specimens for me, but quite failed. So you see what a favour you
have conferred on me. With Drosera it is nothing less than marvellous how
minute a fraction of a grain of any nitrogenised matter the plant can
detect; and how differently it behaves when matter, not containing
nitrogen, of the same consistence, whether fluid or solid, is applied to
the glands. It is also exquisitely sensitive to a weight of even the
1/70000 of a grain. From what I can see of the glands on Drosophyllum I
suspect that I shall find only the commencement, or nascent state of the
wonderful capacities of the Drosera, and this will be eminently interesting
to me. My MS. on this subject has been nearly ready for publication during
some years, but when I shall have strength and time to publish I know not.

And now to turn to other points in your letter. I am quite ignorant of
ferns, and cannot name your specimen. The variability of ferns passes all
bounds. With respect to your Laugher Pigeons, if the same with the two
sub-breeds which I kept, I feel sure from the structure of the skeleton,
etc., that it is a descendant of C. livia. In regard to beauty, I do not
feel the difficulty which you and some others experience. In the last
edition of my "Origin" I have discussed the question, but necessarily very
briefly. (702/3. Fourth Edition, page 238.) A new and I hope amended
edition of the "Origin" is now passing through the press, and will be
published in a month or two, and it will give me great pleasure to send you
a copy. Is there any place in London where parcels are received for you,
or shall I send it by post? With reference to dogs' tails, no doubt you
are aware that a rudimentary stump is regularly inherited by certain breeds
of sheep-dogs, and by Manx cats. You speak of a change in the position of
the axis of the earth: this is a subject quite beyond me, but I believe
the astronomers reject the idea. Nevertheless, I have long suspected that
some periodical astronomical or cosmical cause must be the agent of the
incessant oscillations of level in the earth's crust. About a month ago I
suggested this to a man well capable of judging, but he could not conceive
any such agency; he promised, however, to keep it in mind. I wish I had
time and strength to write to you more fully. I had intended to send this
letter off at once, but on reflection will keep it till I receive the
plants.

LETTER 703. TO H. MULLER.
Down, March 14th, 1870.

I think you have set yourself a new, very interesting, and difficult line
of research. As far as I know, no one has carefully observed the structure
of insects in relation to flowers, although so many have now attended to
the converse relation. (703/1. See Letter 462, also H. Muller,
"Fertilisation of Flowers," English Translation, page 30, on "The insects
which visit flowers." In Muller's book references are given to several of
his papers on this subject.) As I imagine few or no insects are adapted to
suck the nectar or gather the pollen of any single family of plants, such
striking adaptations can hardly, I presume, be expected in insects as in
flowers.

LETTER 704. TO T.H. FARRER (Lord Farrer).

Down, May 28th, 1870.

I suppose I must have known that the stamens recovered their former
position in Berberis (704/1. See Farrer, "Nature," II., 1870, page 164.
Lord Farrer was before H. Muller in making out the mechanism of the
barberry.), for I formerly tried experiments with anaesthetics, but I had
forgotten the facts, and I quite agree with you that it is a sound argument
that the movement is not for self-fertilisation. The N. American
barberries (Mahonia) offer a good proof to what an extent natural crossing
goes on in this genus; for it is now almost impossible in this country to
procure a true specimen of the two or three forms originally introduced.

I hope the seeds of Passiflora will germinate, for the turning up of the
pendent flower must be full of meaning. (704/2. Darwin had (May 12th,
1870) sent to Farrer an extract from a letter from F. Muller, containing a
description of a Passiflora visited by humming-birds, in which the long
flower-stalk curls up so that "the flower itself is upright." Another
species visited by bees is described as having "dependent flowers." In a
letter, June 29th, 1870, Mr. Farrer had suggested that P. princeps, which
he described as having sub-erect flowers, is fitted for humming-birds'
visits. In another letter, October 13th, 1869, he says that Tacsonia,
which has pendent flowers and no corona, is not fertilised by insects in
English glass-houses, and may be adapted for humming-birds. See "Life and
Letters," III., page 279, for Farrer's remarks on Tacsonia and Passiflora;
also H. Muller's "Fertilisation of Flowers," page 268, for what little is
known on the subject; also Letter 701 in the present volume.) I am so glad
that you are able to occupy yourself a little with flowers: I am sure it
is most wise in you, for your own sake and children's sakes.

Some little time ago Delpino wrote to me praising the Swedish book on the
fertilisation of plants; as my son George can read a little Swedish, I
should like to have it back for a time, just to hear a little what it is
about, if you would be so kind as to return it by book-post. (704/3.
Severin Axell, "Om anordningarna for de Fanerogama Vaxternas Befruktning,"
Stockholm, 1869.)

I am going steadily on with my experiments on the comparative growth of
crossed and self-fertilised plants, and am now coming to some very curious
anomalies and some interesting results. I forget whether I showed you any
of them when you were here for a few hours. You ought to see them, as they
explain at a glance why Nature has taken such extraordinary pains to ensure
frequent crosses between distinct individuals.

If in the course of the summer you should feel any inclination to come here
for a day or two, I hope that you will propose to do so, for we should be
delighted to see you...

LETTER 705. TO ASA GRAY.
Down, December 7th, 1870.

I have been very glad to receive your letter this morning. I have for some
time been wishing to write to you, but have been half worked to death in
correcting my uncouth English for my new book. (705/1. "Descent of Man.")
I have been glad to hear of your cases appearing like incipient dimorphism.
I believe that they are due to mere variability, and have no significance.
I found a good instance in Nolana prostrata, and experimented on it, but
the forms did not differ in fertility. So it was with Amsinckia, of which
you told me. I have long thought that such variations afforded the basis
for the development of dimorphism. I was not aware of such cases in Phlox,
but have often admired the arrangement of the anthers, causing them to be
all raked by an inserted proboscis. I am glad also to hear of your curious
case of variability in ovules, etc.

I said that I had been wishing to write to you, and this was about your
Drosera, which after many fluctuations between life and death, at last made
a shoot which I could observe. The case is rather interesting; but I must
first remind you that the filament of Dionoea is not sensitive to very
light prolonged pressure, or to nitrogenous matter, but is exquisitely
sensitive to the slightest touch. (705/2. In another connection the
following reference to Dionoea is of some interest: "I am sure I never
heard of Curtis's observations on Dionoea, nor have I met with anything
more than general statements about this plant or about Nepenthes catching
insects." (From a letter to Sir J.D. Hooker, July 12th, 1860.)) In our
Drosera the filaments are not sensitive to a slight touch, but are
sensitive to prolonged pressure from the smallest object of any nature;
they are also sensitive to solid or fluid nitrogenous matter. Now in your
Drosera the filaments are not sensitive to a rough touch or to any pressure
from non-nitrogenous matter, but are sensitive to solid or fluid
nitrogenous matter. (705/3. Drosera filiformis: see "Insectivorous
Plants," page 281. The above account does not entirely agree with Darwin's
published statement. The filaments moved when bits of cork or cinder were
placed on them; they did not, however, respond to repeated touches with a
needle, thus behaving differently from D. rotundifolia. It should be
remembered that the last-named species is somewhat variable in reacting to
repeated touches.) Is it not curious that there should be such diversified
sensitiveness in allied plants?

I received a very obliging letter from Mr. Morgan, but did not see him, as
I think he said he was going to start at once for the Continent. I am
sorry to hear rather a poor account of Mrs. Gray, to whom my wife and I
both beg to be very kindly remembered.

LETTER 706. TO C.V. RILEY.

(706/1. In Riley's opinion his most important work was the series entitled
"Annual Report on the Noxious, Beneficial, and other Insects of the State
of Missouri" (Jefferson City), beginning in 1869. These reports were
greatly admired by Mr. Darwin, and his copies of them, especially of Nos. 3
and 4, show signs of careful reading.)

Down, June 1st [1871].

I received some little time ago your report on noxious insects, and have
now read the whole with the greatest interest. (706/2. "Third Annual
Report on the Noxious, Beneficial, and other Insects of the State of
Missouri" (Jefferson City, Mo.). The mimetic case occurs at page 67; the
1875 pupae of Pterophorus periscelidactylus, the "Grapevine Plume," have
pupae either green or reddish brown, the former variety being found on the
leaves, the latter on the brown stems of the vine.) There are a vast
number of facts and generalisations of value to me, and I am struck with
admiration at your powers of observation.

The discussion on mimetic insects seems to me particularly good and
original. Pray accept my cordial thanks for the instruction and interest
which I have received.