More Letters of Charles Darwin Volume II

C >> Charles Darwin >> More Letters of Charles Darwin Volume II

Pages:
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49

What a loss to Natural Science our poor mutual friend Walsh has been; it is
a loss ever to be deplored...

Your country is far ahead of ours in some respects; our Parliament would
think any man mad who should propose to appoint a State Entomologist.

LETTER 707A. TO C.V. RILEY.

(706A/1. We have found it convenient to place the two letters to Riley
together, rather than separate them chronologically.)

Down, September 28th, 1881.

I must write half a dozen lines to say how much interested I have been by
your "Further Notes" on Pronuba which you were so kind as to send me.
(706A/2. "Proc. Amer. Assoc. Adv. Sci." 1880.) I had read the various
criticisms, and though I did not know what answer could be made, yet I felt
full confidence in your result, and now I see that I was right...If you
make any further observation on Pronuba it would, I think, be well worth
while for you to observe whether the moth can or does occasionally bring
pollen from one plant to the stigma of a distinct one (706A/3. Riley
discovered the remarkable fact that the Yucca moth (Pronuba yuccasella)
lays its eggs in the ovary of Yucca flowers, which it has previously
pollinated, thus making sure of a supply of ovules for the larvae.), for I
have shown that the cross-fertilisation of the flowers on the same plant
does very little good; and, if I am not mistaken, you believe that Pronuba
gathers pollen from the same flower which she fertilises.

What interesting and beautiful observations you have made on the
metamorphoses of the grasshopper-destroying insects.

LETTER 707. TO F. HILDEBRAND.
Down, February 9th [1872].

Owing to other occupations I was able to read only yesterday your paper on
the dispersal of the seeds of Compositae. (707/1. "Ueber die
Verbreitungsmittel der Compositenfruchte." "Bot. Zeitung," 1872, page 1.)
Some of the facts which you mention are extremely interesting.

I write now to suggest as worthy of your examination the curious adhesive
filaments of mucus emitted by the achenia of many Compositae, of which no
doubt you are aware. My attention was first called to the subject by the
achenia of an Australian Pumilio (P. argyrolepis), which I briefly
described in the "Gardeners' Chronicle," 1861, page 5. As the threads of
mucus dry and contract they draw the seeds up into a vertical position on
the ground. It subsequently occurred to me that if these seeds were to
fall on the wet hairs of any quadruped they would adhere firmly, and might
be carried to any distance. I was informed that Decaisne has written a
paper on these adhesive threads. What is the meaning of the mucus so
copiously emitted from the moistened seeds of Iberis, and of at least some
species of Linum? Does the mucus serve as a protection against their being
devoured, or as a means of attachment. (707/2. Various theories have been
suggested, e.g., that the slime by anchoring the seed to the soil
facilitates the entrance of the radicle into the soil: the slime has also
been supposed to act as a temporary water-store. See Klebs in Pfeffer's
"Untersuchungen aus dem Bot. Inst. zu Tubingen," I., page 581.) I have
been prevented reading your paper sooner by attempting to read Dr.
Askenasy's pamphlet, but the German is too difficult for me to make it all
out. (707/3. E. Askenasy, "Beitrage zur Kritik der Darwin'schen Lehre."
Leipzig, 1872.) He seems to follow Nageli completely. I cannot but think
that both much underrate the utility of various parts of plants; and that
they greatly underrate the unknown laws of correlated growth, which leads
to all sorts of modifications, when some one structure or the whole plant
is modified for some particular object.

LETTER 708. TO T.H. FARRER. (Lord Farrer).

(708/1. The following letter refers to a series of excellent observations
on the fertilisation of Leguminosae, made by Lord Farrer in the autumn of
1869, in ignorance of Delpino's work on the subject. The result was
published in "Nature," October 10th and 17th, 1872, and is full of
interesting suggestions. The discovery of the mechanism in Coronilla
mentioned in a note was one of the cases in which Lord Farrer was
forestalled.)

Down [1872].

I declare I am almost as sorry as if I had been myself forestalled--indeed,
more so, for I am used to it. It is, however, a paramount, though
bothersome duty in every naturalist to try and make out all that has been
done by others on the subject. By all means publish next summer your
confirmation and a summary of Delpino's observations, with any new ones of
your own. Especially attend about the nectary exterior to the staminal
tube. (708/2. This refers to a species of Coronilla in which Lord Farrer
made the remarkable discovery that the nectar is secreted on the outside of
the calyx. See "Nature," July 2nd, 1874, page 169; also Letter 715.) This
will in every way be far better than writing to Delpino. It would not be
at all presumptuous in you to criticise Delpino. I am glad you think him
so clever; for so it struck me.

Look at hind legs yourself of some humble and hive-bees; in former take a
very big individual (if any can be found) for these are the females, the
males being smaller, and they have no pollen-collecting apparatus. I do
not remember where it is figured--probably in Kirby & Spence--but actual
inspection better...

Please do not return any of my books until all are finished, and do not
hurry.

I feel certain you will make fine discoveries.

LETTER 709. TO T.H. FARRER. (Lord Farrer).
Sevenoaks, October 13th, 1872.

I must send you a line to say how extremely good your article appears to me
to be. It is even better than I thought, and I remember thinking it very
good. I am particularly glad of the excellent summary of evidence about
the common pea, as it will do for me hereafter to quote; nocturnal insects
will not do. I suspect that the aboriginal parent had bluish flowers. I
have seen several times bees visiting common and sweet peas, and yet
varieties, purposely grown close together, hardly ever intercross. This is
a point which for years has half driven me mad, and I have discussed it in
my "Var. of Animals and Plants under Dom." (709/1. In the second edition
(1875) of the "Variation of Animals and Plants," Volume I., page 348,
Darwin added, with respect to the rarity of spontaneous crosses in Pisum:
"I have reason to believe that this is due to their stignas being
prematurely fertilised in this country by pollen from the same flower."
This explanation is, we think, almost certainly applicable to Lathyrus
odoratus, though in Darwin's latest publication on the subject he gives
reasons to the contrary. See "Cross and Self-Fertilisation," page 156,
where the problem is left unsolved. Compare Letter 714 to Delpino. In
"Life and Letters," III., page 261, the absence of cross-fertilisation is
explained as due to want of perfect adaptation between the pea and our
native insects. This is Hermann Muller's view: see his "Fertilisation of
Flowers," page 214. See Letter 583, note.) I now suspect (and I wish I
had strength to experimentise next spring) that from changed climate both
species are prematurely fertilised, and therefore hardly ever cross. When
artificially crossed by removal of own pollen in bud, the offspring are
very vigorous.

Farewell.--I wish I could compel you to go on working at fertilisation
instead of so insignificant a subject as the commerce of the country!

You pay me a very pretty compliment at the beginning of your paper.

LETTER 710. TO J.D. HOOKER.

(710/1. The following letters to Sir J.D. Hooker and the late Mr.
Moggridge refer to Moggridge's observation that seeds stored in the nest
of the ant Atta at Mentone do not germinate, though they are certainly
not dead. Moggridge's observations are given in his book, "Harvesting
Ants and Trap-Door Spiders," 1873, which is full of interesting details.
The book is moreover remarkable in having resuscitated our knowledge of
the existence of the seed-storing habit. Mr. Moggridge points out that
the ancients were familiar with the facts, and quotes the well-known
fable of the ant and the grasshopper, which La Fontaine borrowed from
Aesop. Mr. Moggridge (page 5) goes on: "So long as Europe was taught
Natural History by southern writers the belief prevailed; but no sooner
did the tide begin to turn, and the current of information to flood from
north to south, than the story became discredited."

In Moggridge's "supplement" on the same subject, published in 1874, the
author gives an account of his experiments made at Darwin's suggestion,
and concludes (page 174) that "the vapour of formic acid is incapable of
rendering the seeds dormant after the manner of the ants," and that
indeed "its influence is always injurious to the seeds, even when
present only in excessively minute quantities." Though unable to
explain the method employed, he was convinced "that the non-germination
of the seeds is due to some direct influence voluntarily exercised by
the ants, and not merely to the conditions found in the nest" (page
172). See Volume I., Letter 251.)

Down, February 21st [1873].

You have given me exactly the information which I wanted.

Geniuses jump. I have just procured formic acid to try whether its
vapour or minute drops will delay germination of fresh seeds; trying
others at same time for comparison. But I shall not be able to try them
till middle of April, as my despotic wife insists on taking a house in
London for a month from the middle of March.

I am glad to hear of the Primer (710/2. "Botany" (Macmillan's Science
Primers).); it is not at all, I think, a folly. Do you know Asa Gray's
child book on the functions of plants, or some such title? It is very
good in giving an interest to the subject.

By the way, can you lend me the January number of the "London Journal of
Botany" for an article on insect-agency in fertilisation?

LETTER 711. TO J. TRAHERNE MOGGRIDGE.
Down, August 27th, 1873.

I thank you for your very interesting letter, and I honour you for your
laborious and careful experiments. No one knows till he tries how many
unexpected obstacles arise in subjecting plants to experiments.

I can think of no suggestions to make; but I may just mention that I had
intended to try the effects of touching the dampened seeds with the
minutest drop of formic acid at the end of a sharp glass rod, so as to
imitate the possible action of the sting of the ant. I heartily hope
that you may be rewarded by coming to some definite result; but I fail
five times out of six in my own experiments. I have lately been trying
some with poor success, and suppose that I have done too much, for I
have been completely knocked up for some days.

LETTER 712. TO J. TRAHERNE MOGGRIDGE.
Down, March 10th, 1874.

I am very sorry to hear that the vapour experiments have failed; but
nothing could be better, as it seems to me, than your plan of enclosing
a number of the ants with the seeds. The incidental results on the
power of different vapours in killing seeds and stopping germination
appear very curious, and as far as I know are quite new.

P.S.--I never before heard of seeds not germinating except during a
certain season; it will be a very strange fact if you can prove this.
(712/1. Certain seeds pass through a resting period before germination.
See Pfeffer's "Pflanzenphysiologie," Edition I., Volume II., page III.)

LETTER 713. TO H. MULLER.
Down, May 30th, 1873.

I am much obliged for your letter received this morning. I write now
chiefly to give myself the pleasure of telling you how cordially I
admire the last part of your book, which I have finished. (713/1. "Die
Befruchtung der Blumen durch Insekten": Leipzig, 1873. An English
translation was published in 1883 by Prof. D'Arcy Thompson. The
"Prefatory Notice" to this work (February 6th, 1882) is almost the last
of Mr. Darwin's writings. See "Life and Letters," page 281.) The whole
discussion seems to me quite excellent, and it has pleased me not a
little to find that in the rough MS. of my last chapter I have arrived
on many points at nearly the same conclusions that you have done, though
we have reached them by different routes. (713/2. "The Effects of
Cross and Self-Fertilisation in the Vegetable Kingdom": London, 1876.)

LETTER 714. TO F. DELPINO.
Down, June 25th [1873].

I thank you sincerely for your letter. I am very glad to hear about
Lathyrus odoratus, for here in England the vars. never cross, and yet
are sometimes visited by bees. (714/1. In "Cross and
Self-Fertilisation," page 156, Darwin quotes the information received
from Delpino and referred to in the present letter--namely, that it is
the fixed opinion of the Italian gardeners that the varieties do
intercross. See Letter 709.) Pisum sativum I have also many times seen
visited by Bombus. I believe the cause of the many vars. not crossing
is that under our climate the flowers are self-fertilised at an early
period, before the corolla is fully expanded. I shall examine this
point with L. odoratus. I have read H. Muller's book, and it seems to
me very good. Your criticism had not occurred to me, but is, I think
just--viz. that it is much more important to know what insects
habitually visit any flower than the various kinds which occasionally
visit it. Have you seen A. Kerner's book "Schutzmittel des Pollens,"
1873, Innsbruck. (714/2. Afterwards translated by Dr. Ogle as "Flowers
and their Unbidden Guests," with a prefatory letter by Charles Darwin,
1878.) It is very interesting, but he does not seem to know anything
about the work of other authors.

I have Bentham's paper in my house, but have not yet had time to read a
word of it. He is a man with very sound judgment, and fully admits the
principle of evolution.

I have lately had occasion to look over again your discussion on
anemophilous plants, and I have again felt much admiration at your work.
(714/3. "Atti della Soc. Italiana di Scienze Nat." Volume XIII.)

(714/4. In the beginning of August, 1873, Darwin paid the first of
several visits to Lord Farrer's house at Abinger. When sending copies
of Darwin's letters for the "Life and Letters," Lord Farrer was good
enough to add explanatory notes and recollections, from which we quote
the following sketch.)

"Above my house are some low hills, standing up in the valley, below the
chalk range on the one hand and the more distant range of Leith Hill on
the other, with pretty views of the valley towards Dorking in one
direction and Guildford in the other. They are composed of the less
fertile Greensand strata, and are covered with fern, broom, gorse, and
heath. Here it was a particular pleasure of his to wander, and his tall
figure, with his broad-brimmed Panama hat and long stick like an
alpenstock, sauntering solitary and slow over our favourite walks, is
one of the pleasantest of the many pleasant associations I have with the
place."

LETTER 715. TO T.H. FARRER (Lord Farrer).

(715/1. The following note by Lord Farrer explains the main point of
the letter, which, however, refers to the "bloom" problem as well as to
Coronilla:--

"I thought I had found out what puzzled us in Coronilla varia: in most
of the Papilionaceae, when the tenth stamen is free, there is nectar in
the staminal tube, and the opening caused by the free stamen enables the
bee to reach the nectar, and in so doing the bee fertilises the plant.
In Coronilla varia, and in several other species of Coronilla, there is
no nectar in the staminal tube or in the tube of the corolla. But there
are peculiar glands with nectar on the outside of the calyx, and
peculiar openings in the tube of the corolla through which the proboscis
of the bee, whilst entering the flower in the usual way and dusting
itself with pollen, can reach these glands, thus fertilising the plant
in getting the nectar. On writing this to Mr. Darwin, I received the
following characteristic note.

The first postscript relates to the rough ground behind my house, over
which he was fond of strolling. It had been ploughed up and then
allowed to go back, and the interest was to watch how the numerous
species of weeds of cultivation which followed the plough gradually gave
way in the struggle for existence to the well-known and much less varied
flora of an English common.")

Bassett, Southampton, August 14th, 1873.

You are the man to conquer a Coronilla. (715/2. In a former letter to
Lord Farrer, Darwin wrote: "Here is a maxim for you, 'It is disgraceful
to be beaten by a Coronilla.'") I have been looking at the half-dried
flowers, and am prepared to swear that you have solved the mystery. The
difference in the size of the cells on the calyx under the vexillum
right down to the common peduncle is conspicuous. The flour still
adhered to this side; I see little bracteae or stipules apparently with
glandular ends at the base of the calyces. Do these secrete? It seems
to me a beautiful case. When I saw the odd shape of the base of the
vexillum, I concluded that it must have some meaning, but little dreamt
what that was. Now there remains only the one serious point--viz.the
separation of the one stamen. I daresay that you are right in that
nectar was originally secreted within the staminal tube; but why has not
the one stamen long since cohered? The great difference in structure
for fertilisation within the same genus makes one believe that all such
points are vary variable. (715/3. Coronilla emerus is of the ordinary
papilionaceous type.) With respect to the non-coherence of the one
stamen, do examine some flower-buds at a very early age; for parts which
are largely developed are often developed to an unusual degree at a very
early age, and it seems to me quite possible that the base of the
vexillum (to which the single stamen adhered) might thus be developed,
and thus keep it separate for a time from the other stamens. The
cohering stamens to the right and left of the single one seem to me to
be pushed out a little laterally. When you have finished your
observations, you really ought to send an account with a diagram to
"Nature," recalling your generalisation about the diadelphous structure,
and now explaining the exception of Coronilla. (715/4. The
observations were published in "Nature," Volume X., 1874, page 169.)

Do add a remark how almost every detail of structure has a meaning where
a flower is well examined.

Your observations pleased me so much that I could not sit still for half
an hour.

Please to thank Mr. Payne (715/5. Lord Farrer's gardener.) for his
remarks, which are of value to me, with reference to Mimosa. I am very
much in doubt whether opening the sashes can act by favouring the
evaporation of the drops; may not the movement of the leaves shake off
the drops, or change their places? If Mr. Payne remembers any plant
which is easily injured by drops, I wish he would put a drop or two on a
leaf on a bright day, and cover the plant with a clean bell-glass, and
do the same for another plant, but without a bell-glass over it, and
observe the effects.

Thank you much for wishing to see us again at Abinger, and it is very
doubtful whether it will be Coronilla, Mr. Payne, the new garden, the
children, E. [Lady Farrer], or yourself which will give me the most
pleasure to see again.

P.S. 1.--It will be curious to note in how many years the rough ground
becomes quite uniform in its flora.

P.S. 2.--One may feel sure that periodically nectar was secreted within
the flower and then secreted by the calyx, as in some species of Iris
and orchids. This latter being taken advantage of in Coronilla would
allow of the secretion within the flower ceasing, and as this change was
going on in the two secretions, all the parts of the flower would become
modified and correlated.

LETTER 716. TO J. BURDON SANDERSON.
Down, Tuesday, September 9th [1873].

(716/1. Sir J. Burdon Sanderson showed that in Dionoea movement is
accompanied by electric disturbances closely analogous to those
occurring in muscle (see "Nature," 1874, pages 105, 127; "Proc. R. Soc."
XXI., and "Phil. Trans." Volume CLXXIII., 1883, where the results are
finally discussed).)

I will send up early to-morrow two plants [of Dionoea] with five goodish
leaves, which you will know by their being tied to sticks. Please
remember that the slightest touch, even by a hair, of the three
filaments on each lobe makes the leaf close, and it will not open for
twenty-four hours. You had better put 1/4 in. of water into the saucers
of the pots. The plants have been kept too cool in order to retard
them. You had better keep them rather warm (i.e. temperature of warm
greenhouse) for a day, and in a good light.

I am extremely glad you have undertaken this subject. If you get a
positive result, I should think you ought to publish it separately, and
I could quote it; or I should be most glad to introduce any note by you
into my account.

I have no idea whether it is troublesome to try with the thermo-electric
pile any change of temperature when the leaf closes. I could detect
none with a common thermometer. But if there is any change of
temperature I should expect it would occur some eight to twelve or
twenty-four hours after the leaf has been given a big smashed fly, and
when it is copiously secreting its acid digestive fluid.

I forgot to say that, as far as I can make out, the inferior surface of
the leaf is always in a state of tension, and that the contraction is
confined to the upper surface; so that when this contraction ceases or
suddenly fails (as by immersion in boiling water) the leaf opens again,
or more widely than is natural to it.

Whenever you have quite finished, I will send for the plants in their
basket. My son Frank is staying at 6, Queen Anne Street, and comes home
on Saturday afternoon, but you will not have finished by that time.

P.S. I have repeated my experiment on digestion in Drosera with
complete success. By giving leaves a very little weak hydrochloric
acid, I can make them digest albumen--i.e. white of egg--quicker than
they can do naturally. I most heartily thank you for all your kindness.
I have been pretty bad lately, and must work very little.

LETTER 717. TO J. BURDON SANDERSON.
September 13th [1873].

How very kind it was of you to telegraph to me. I am quite delighted
that you have got a decided result. Is it not a very remarkable fact?
It seems so to me, in my ignorance. I wish I could remember more
distinctly what I formerly read of Du Bois Raymond's results. My poor
memory never serves me for more than a vague guide. I really think you
ought to try Drosera. In a weak solution of phosphate of ammonia (viz.
1 gr. to 20 oz. of water) it will contract in about five minutes, and
even more quickly in pure warm water; but then water, I suppose, would
prevent your trial. I forget, but I think it contracts pretty quickly
(i.e. in an hour or two) with a large drop of a rather stronger solution
of the phosphate, or with an atom of raw meat on the disc of the leaf.

LETTER 718. TO J.D. HOOKER.
October 31st, 1873.

Now I want to tell you, for my own pleasure, about the movements of
Desmodium.

1. When the plant goes to sleep, the terminal leaflets hang vertically
down, but the petioles move up towards the axis, so that the dependent
leaves are all crowded round it. The little leaflets never go to sleep,
and this seems to me very odd; they are at their games of play as late
as 11 o'clock at night and probably later. (718/1. Stahl ("Botanische
Zeitung," 1897, page 97) has suggested that the movements of the dwarf
leaflets in Desmodium serve to shake the large terminal leaflets, and
thus increase transpiration. According to Stahl's view their movement
would be more useful at night than by day, because stagnation of the
transpiration-current is more likely to occur at night.)

2. If the plant is shaken or syringed with tepid water, the terminal
leaflets move down through about an angle of 45 deg, and the petioles
likewise move about 11 deg downwards; so that they move in an opposite
direction to what they do when they go to sleep. Cold water or air
produces the same effect as does shaking. The little leaflets are not
in the least affected by the plant being shaken or syringed. I have no
doubt, from various facts, that the downward movement of the terminal
leaflets and petioles from shaking and syringing is to save them from
injury from warm rain.

3. The axis, the main petiole, and the terminal leaflets are all, when
the temperature is high, in constant movement, just like that of
climbing plants. This movement seems to be of no service, any more than
the incessant movement of amoeboid bodies. The movement of the terminal
leaflets, though insensible to the eye, is exactly the same as that of
the little lateral leaflets--viz. from side to side, up and down, and
half round their own axes. The only difference is that the little
leaflets move to a much greater extent, and perhaps more rapidly; and
they are excited into movement by warm water, which is not the case with
the terminal leaflet. Why the little leaflets, which are rudimentary in
size and have lost their sleep-movements and their movements from being
shaken, should not only have retained, but have their spontaneous
movements exaggerated, I cannot conceive. It is hardly credible that it
is a case of compensation. All this makes me very anxious to examine
some plant (if possible one of the Leguminosae) with either the terminal
or lateral leaflets greatly reduced in size, in comparison with the
other leaflets on the same leaf. Can you or any of your colleagues
think of any such plant? It is indirectly on this account that I so
much want the seeds of Lathyrus nissolia.