More Letters of Charles Darwin Volume II

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LETTER 735. TO D. OLIVER.
Down, October, 13th [1876?].

You must be a clair-voyant or something of that kind to have sent me
such useful plants. Twenty-five years ago I described in my father's
garden two forms of Linum flavum (thinking it a case of mere variation);
from that day to this I have several times looked, but never saw the
second form till it arrived from Kew. Virtue is never its own reward:
I took paper this summer to write to you to ask you to send me flowers,
[so] that I might beg plants of this Linum, if you had the other form,
and refrained, from not wishing to trouble you. But I am now sorry I
did, for I have hardly any doubt that L. flavum never seeds in any
garden that I have seen, because one form alone is cultivated by slips.
(735/1. Id est, because, the plant being grown from slips, one form
alone usually occurs in any one garden. It is also arguable that it is
grown by slips because only one form is common, and therefore seedlings
cannot be raised.)

(736/1. The following five letters refer to Darwin's work on "bloom"--a
subject on which he did not live to complete his researches:--

One of his earliest letters on this subject was addressed in August,
1873, to Sir Joseph Hooker (736/2. Published in "Life and Letters,"
III., page 339.):

"I want a little information from you, and if you do not yourself know,
please to enquire of some of the wise men of Kew.

"Why are the leaves and fruit of so many plants protected by a thin
layer of waxy matter (like the common cabbage), or with fine hair, so
that when such leaves or fruit are immersed in water they appear as if
encased in thin glass? It is really a pretty sight to put a pod of the
common pea, or a raspberry, into water. I find several leaves are thus
protected on the under surface and not on the upper.

"How can water injure the leaves, if indeed this is at all the case?"

On this latter point Darwin wrote to the late Lord Farrer:

"I am now become mad about drops of water injuring leaves. Please ask
Mr. Payne (736/3. Lord Farrer's gardener.) whether he believes, FROM
HIS OWN EXPERIENCE, that drops of water injure leaves or fruit in his
conservatories. It is said that the drops act as burning-glasses; if
this is true, they would not be at all injurious on cloudy days. As he
is so acute a man, I should very much like to hear his opinion. I
remember when I grew hothouse orchids I was cautioned not to wet their
leaves; but I never then thought on the subject."

The next letter, though of later date than some which follow it, is
printed here because it briefly sums his results and serves as guide to
the letters dealing with the subject.)

LETTER 736. TO W. THISELTON-DYER.

(736/4. Published in "Life and Letters," III., page 341.)

Down, September 5th [1877].

One word to thank you. I declare, had it not been for your kindness, we
should have broken down. As it is we have made out clearly that with
some plants (chiefly succulent) the bloom checks evaporation--with some
certainly prevents attacks of insects; with SOME sea-shore plants
prevents injury from salt water, and, I believe, with a few prevents
injury from pure water resting on the leaves. This latter is as yet the
most doubtful and the most interesting point in relation to the
movements of plants.

(736/5. Modern research, especially that of Stahl on transpiration
("Bot. Zeitung," 1897, page 71) has shown that the question is more
complex than it appeared in 1877. Stahl's point of view is that
moisture remaining on a leaf checks the transpiration-current; and by
thus diminishing the flow of mineral nutriment interferes with the
process of assimilation. Stahl's idea is doubtless applicable to the
whole problem of bloom on leaves. For other references to bloom see
letters 685, 689 and 693.)

LETTER 737. TO J.D. HOOKER.
Down, August 19th, 1873.

The next time you walk round the garden ask Mr. Smith (737/1. Probably
John Smith (1798-1888), for some years Curator, Royal Gardens, Kew.), or
any of your best men, what they think about injury from watering during
sunshine. One of your men--viz., Mr. Payne, at Abinger, who seems very
acute--declares that you may water safely any plant out of doors in
sunshine, and that you may do the same for plants under glass if the
sashes are opened. This seems to me very odd, but he seems positive on
the point, and acts on it in raising splendid grapes. Another good
gardener maintains that it is only COLD water dripping often on the same
point of a leaf that ever injures it. I am utterly perplexed, but
interested on the point. Give me what you learn when you come to Down.

I should like to hear what plants are believed to be most injured by
being watered in sunshine, so that I might get such.

I expect that I shall be utterly beaten, as on so many other points; but
I intend to make a few experiments and observations. I have already
convinced myself that drops of water do NOT act as burning lenses.

LETTER 738. TO J.D. HOOKER.
December 20th [1873].

I find that it is no use going on with my experiments on the evil
effects of water on bloom-divested leaves. Either I erred in the early
autumn or summer in some incomprehensible manner, or, as I suspect to be
the case, water is only injurious to leaves when there is a good supply
of actinic rays. I cannot believe that I am all in the wrong about the
movements of the leaves to shoot off water.

The upshot of all this is that I want to keep all the plants from Kew
until the spring or early summer, as it is mere waste of time going on
at present.

LETTER 739. TO W. THISELTON-DYER.
Down, July 22nd [1877].

Many thanks for seeds of the Malva and information about Averrhoa, which
I perceived was sensitive, as A. carambola is said to be; and about
Mimosa sensitiva. The log-wood [Haematoxylon] has interested me much.
The wax is very easily removed, especially from the older leaves, and I
found after squirting on the leaves with water at 95 deg, all the older
leaves became coated, after forty-eight hours, in an astonishing manner
with a black Uredo, so that they looked as if sprinkled with soot and
water. But not one of the younger leaves was affected. This has set me
to work to see whether the "bloom" is not a protection against
parasites. As soon as I have ascertained a little more about the case
(and generally I am quite wrong at first) I will ask whether I could
have a very small plant, which should never be syringed with water above
60 deg, and then I suspect the leaves would not be spotted, as were the
older ones on the plant, when it arrived from Kew, but nothing like what
they were after my squirting.

In an old note of yours (which I have just found) you say that you have
a sensitive Schrankia: could this be lent me?

I have had lent me a young Coral-tree (Erythrina), which is very sickly,
yet shows odd sleep movements. I suppose I could buy one, but Hooker
told me first to ask you for anything.

Lastly, have you any seaside plants with bloom? I find that drops of
sea-water corrode sea-kale if bloom is removed; also the var. littorum
of Triticum repens. (By the way, my plants of the latter, grown in pots
here, are now throwing up long flexible green blades, and it is very odd
to see, ON THE SAME CULM, the rigid grey bloom-covered blades and the
green flexible ones.) Cabbages, ill-luck to them, do not seem to be
hurt by salt water. Hooker formerly told me that Salsola kali, a var.
of Salicornia, one species of Suaeda, Euphorbia peplis, Lathyrus
maritimus, Eryngium maritimum, were all glaucous and seaside plants. It
is very improbable that you have any of these or of foreigners with the
same attributes.

God forgive me: I hope that I have not bored you greatly.

By all the rules of right the leaves of the logwood ought to move (as if
partially going to sleep) when syringed with tepid water. The leaves of
my little plant do not move at all, and it occurs to me as possible,
though very improbable, that it would be different with a larger plant
with perhaps larger leaves. Would you some day get a gardener to
syringe violently, with water kept in a hothouse, a branch on one of
your largest logwood plants and observe [whether?] leaves move together
towards the apex of leaf?

By the way, what astonishing nonsense Mr. Andrew Murray has been writing
about leaves and carbonic acid! I like to see a man behaving
consistently...

What a lot I have scribbled to you!

(FIGURE 13. Leaf of Trifolium resupinatum (from a drawing by Miss
Pertz).)

LETTER 740. TO W. THISELTON-DYER.
[August, 1877.]

There is no end to my requests. Can you spare me a good plant (or even
two) of Oxalis sensitiva? The one which I have (formerly from Kew) has
been so maltreated that I dare not trust my results any longer.

Please give the enclosed to Mr. Lynch. (740/1. Mr. Lynch, now Curator
of the Cambridge Botanic Garden, was at this time in the R. Bot. Garden,
Kew. Mr. Lynch described the movements of Averrhoa bilimbi in the
"Linn. Soc. Journ," Volume XVI., page 231. See also "The Power of
Movement in Plants," page 330.) The spontaneous movements of the
Averrhoa are very curious.

You sent me seeds of Trifolium resupinatum, and I have raised plants,
and some former observations which I did not dare to trust have proved
accurate. It is a very little fact, but curious. The half of the
lateral leaflets (marked by a cross) on the lower side have no bloom and
are wetted, whereas the other half has bloom and is not wetted, so that
the two sides look different to the naked eye. The cells of the
eipdermis appear of a different shape and size on the two sides of the
leaf [Figure 13].

When we have drawings and measurements of cells made, and are sure of
our facts, I shall ask you whether you know of any case of the same leaf
differing histologically on the two sides, for Hooker always says you
are a wonderful man for knowing what has been made out.

(740/2. The biological meaning of the curious structure of the leaves
of Trifolium resupinatum remains a riddle. The stomata and (speaking
from memory) the trichomes differ on the two halves of the lateral
leaflets.)

LETTER 741. TO L. ERRERA.

(741/1. Professor L. Errera, of Brussels wrote, as a student, to
Darwin, asking permission to send the MS. of an essay by his friend S.
Gevaert and himself on cross and self-fertilisation, and which was
afterwards published in the "Bull. Soc. Bot. Belg." XVII., 1878. The
terms xenogamy, geitonogamy, and autogamy were first suggested by Kerner
in 1876; their definition will be found at page 9 of Ogle's translation
of Kerner's "Flowers and their Unbidden Guests," 1878. In xenogamy the
pollen comes from another PLANT; in geitonogamy from another FLOWER on
the same PLANT; in autogamy from the androecium of the fertilised
FLOWER. Allogamy embraces xenogamy and geitonogamy.)

Down, October 4th, 1877.

I have now read your MS. The whole has interested me greatly, and is
very clearly written. I wish that I had used some such terms as
autogamy, xenogamy, etc...I entirely agree with you on the a priori
probability of geitonogamy being more advantageous than autogamy; and I
cannot remember having ever expressed a belief that autogamy, as a
general rule, was better than geitonogamy; but the cases recorded by me
seem too strong not to make me suspect that there was some unknown
advantage in autogamy. In one place I insert the caution "if this be
really the case," which you quote. (741/2. See "Cross and
Self-Fertilisation," pages 352, 386. The phrase referred to occurs in
both passages; that on page 386 is as follows: "We have also seen
reason to suspect that self-fertilisation is in some peculiar manner
beneficial to certain plants; but if this be really the case, the
benefit thus derived is far more than counterbalanced by a cross with a
fresh stock or with a slightly different variety." Errera and Gevaert
conclude (pages 79-80) that the balance of the available evidence is in
favour of the belief that geitonogamy is intermediate, in effectiveness,
between autogamy and xenogamy.) I shall be very glad to be proved to be
altogether in error on this point.

Accept my thanks for pointing out the bad erratum at page 301. I hope
that you will experimentise on inconspicuous flowers (741/3. See Miss
Bateson, "Annals of Botany," 1888, page 255, "On the Cross-Fertilisation
of Inconspicuous Flowers:" Miss Bateson showed that Senecio vulgaris
clearly profits by cross-fertilisation; Stellaria media and Capsella
bursa-pastoris less certainly.); if I were not too old and too much
occupied I would do so myself.

Finally let me thank you for the kind manner in which you refer to my
work, and with cordial good wishes for your success...

LETTER 742. TO W. THISELTON-DYER.
Down, October 9th, 1877.

One line to thank you much about Mertensia. The former plant has begun
to make new leaves, to my great surprise, so that I shall be now well
supplied. We have worked so well with the Averrhoa that unless the
second species arrives in a very good state it would be superfluous to
send it. I am heartily glad that you and Mrs. Dyer are going to have a
holiday. I will look at you as a dead man for the next month, and
nothing shall tempt me to trouble you. But before you enter your grave
aid me if you can. I want seeds of three or four plants (not
Leguminosae or Cruciferae) which produce large cotyledons. I know not
in the least what plants have large cotyledons. Why I want to know is
as follows: The cotyledons of Cassia go to sleep, and are sensitive to
a touch; but what has surprised me much is that they are in constant
movement up and down. So it is with the cotyledons of the cabbage, and
therefore I am very curious to ascertain how far this is general.

LETTER 743. TO W. THISELTON-DYER.
Down, October 11th [1877].

The fine lot of seeds arrived yesterday, and are all sown, and will be
most useful. If you remember, pray thank Mr. Lynch for his aid. I had
not thought of beech or sycamore, but they are now sown.

Perhaps you may like to see a rough copy of the tracing of movements of
one of the cotyledons of red cabbage, and you can throw it into the
fire. A line joining the two cotyledons stood facing a north-east
window, and the day was uniformly cloudy. A bristle was gummed to one
cotyledon, and beyond it a triangular bit of card was fixed, and in
front a vertical glass. A dot was made in the glass every quarter or
half hour at the point where the end of the bristle and the apex of card
coincided, and the dots were joined by straight lines. The observations
were from 10 a.m. to 8.45 p.m. During this time the enclosed figure was
described; but between 4 p.m. and 5.38 p.m. the cotyledon moved so that
the prolonged line was beyond the limits of the glass, and the course is
here shown by an imaginary dotted line. The cotyledon of Primula
sinensis moved in closely analogous manner, as do those of a Cassia.
Hence I expect to find such movements very general with cotyledons, and
I am inclined to look at them as the foundation for all the other
adaptive movements of leaves. They certainly are of the so-called sleep
of plants.

I hope I have not bothered you. Do not answer. I am all on fire at the
work.

I have had a short and very prosperous note from Asa Gray, who says
Hooker is very prosperous, and both are tremendously hard at work.
(743/1. "Hooker is coming over, and we are going in summer to the Rocky
Mountains together, according to an old promise of mine." Asa Gray to
G.F. Wright, May 24th, 1877 ("Letters of Asa Gray," II., page 666).)

LETTER 744. TO H. MULLER.
Down, January 1st [1878?].

I must write two or three lines to thank you cordially for your very
handsome and very interesting review of my last book in "Kosmos," which
I have this minute finished. (744/1. "Forms of Flowers," 1877. H.
Muller's article is in "Kosmos," II., page 286.) It is wonderful how
you have picked out everything important in it. I am especially glad
that you have called attention to the parallelism between illegitimate
offspring of heterostyled plants and hybrids. Your previous article in
"Kosmos" seemed to me very important, but for some unknown reason the
german was very difficult, and I was sadly overworked at the time, so
that I could not understand a good deal of it. (744/2. "Kosmos," II.,
pages 11, 128. See "Forms of Flowers," Edition II., page 308.) But I
have put it on one side, and when I have to prepare a new edition of my
book I must make it out. It seems that you attribute such cases as that
of the dioecious Rhamnus and your own of Valeriana to the existence of
two forms with larger and smaller flowers. I cannot follow the steps by
which such plants have been rendered dioecious, but when I read your
article with more care I hope I shall understand. (744/3. See "Forms
of Flowers," Edition II., pages 9 and 304. H. Muller's view is briefly
that conspicuous and less conspicuous varieties occurred, and that the
former were habitually visited first by insects; thus the less
conspicuous form would play the part of females and their pollen would
tend to become superfluous. See H. Muller in "Kosmos," II.) If you
have succeeded in explaining this class of cases I shall heartily
rejoice, for they utterly perplexed me, and I could not conjecture what
their meaning was. It is a grievous evil to have no faculty for new
languages.

With the most sincere respect and hearty good wishes to you and all your
family for the new year...

P.S.--What interesting papers your wonderful brother has lately been
writing!

LETTER 745. TO W. THISELTON-DYER.

(745/1. This letter refers to the purchase of instruments for the
Jodrell Laboratory in the Royal Gardens, Kew. "The Royal Commission on
Scientific Instruction and the Advancement of Science, commonly spoken
of as the Devonshire Commission, in its fourth Report (1874), page 10,
expressed the opinion that 'it is highly desirable that opportunities
for the pursuit of investigations in Physiological Botany should be
afforded at Kew to those persons who may be inclined to follow that
branch of science.' Effect was given to this recommendation by the
liberality of the late T.J. Phillips-Jodrell, M.A., who built and
equipped the small laboratory, which has since borne his name, at his
own expense. It was completed and immediately brought into use in
1876." The above is taken from the "Bulletin of Miscellaneous
Information," R. Botanic Gardens, Kew, 1901, page 102, which also gives
a list of work carried out in the laboratory between 1876 and 1900.)

Down, March 14th, 1878.

I have a very strong opinion that it would be the greatest possible pity
if the Phys[iological] Lab., now that it has been built, were not
supplied with as many good instruments as your funds can possibly
afford. It is quite possible that some of them may become antiquated
before they are much or even at all used. But this does not seem to me
any argument at all against getting them, for the Laboratory cannot be
used until well provided; and the mere fact of the instruments being
ready may suggest to some one to use them. You at Kew, as guardians and
promoters of botanical science, will then have done all in your power,
and if your Lab. is not used the disgrace will lie at the feet of the
public. But until bitter experience proves the contrary I will never
believe that we are so backward. I should think the German laboratories
would be very good guides as to what to get; but Timiriazeff of Moscow,
who travelled over Europe to see all Bot. Labs., and who seemed so good
a fellow, would, I should think, give the best list of the most
indispensable instruments. Lately I thought of getting Frank or Horace
to go to Cambridge for the use of the heliostat there; but our
observations turned out of less importance than I thought, yet if there
had been one at Kew we should probably have used it, and might have
found out something curious. It is impossible for me to predict whether
or not we should ever want this or that instrument, for we are guided in
our work by what turns up. Thus I am now observing something about
geotropism, and I had no idea a few weeks ago that this would have been
necessary. In a short time we might earnestly wish for a centrifugal
apparatus or a heliostat. In all such cases it would make a great
difference if a man knew that he could use a particular instrument
without great loss of time. I have now given my opinion, which is very
decided, whether right or wrong, and Frank quite agrees with me. You
can, of course, show this letter to Hooker.

LETTER 746. TO F. LUDWIG.
Down, May 29th, 1878.

I thank you sincerely for the trouble which you have taken in sending me
so long and interesting a letter, together with the specimens.
Gradations are always very valuable, and you have been remarkably
successful in discovering the stages by which the Plantago has become
gyno-dioecious. (746/1. See F. Ludwig, "Zeitsch. f. d. Geo.
Naturwiss." Bd. LII., 1879. Professor Ludwig's observations are quoted
in the preface to "Forms of Flowers," Edition II., page ix.) Your view
of its origin, from being proterogynous, seems to me very probable,
especially as the females are generally the later-flowering plants. If
you can prove the reverse case with Thymus your view will manifestly be
rendered still more probable. I have never felt satisfied with H.
Muller's view, though he is so careful and admirable an observer.
(746/2. See "Forms of Flowers," Edition II., page 308. Also letter
744.) It is more than seventeen years since I attended to Plantago, and
when nothing had been published on the subject, and in consequence I
omitted to attend to several points; and now, after so long an interval,
I cannot pretend to say to which of your forms the English one belongs;
I well remember that the anther of the females contained a good deal
[of] pollen, though not one sound grain.

P.S.--Delpino is Professor of Botany in Genoa, Italy (746/3. Now at
Naples.); I have always found him a most obliging correspondent.

LETTER 747. TO W. THISELTON-DYER.
Down, August 24th [1878].

Many thanks for seeds of Trifolium resupinatum, which are invaluable to
us. I enclose seeds of a Cassia, from Fritz Muller, and they are well
worth your cultivation; for he says they come from a unique, large and
beautiful tree in the interior, and though looking out for years, he has
never seen another specimen. One of the most splendid, largest and
rarest butterflies in S. Brazil, he has never seen except near this one
tree, and he has just discovered that its caterpillars feed on its
leaves.

I have just been looking at fine young pods beneath the ground of
Arachis. (747/1. Arachis hypogoea, cultivated for its "ground nuts.")
I suppose that the pods are not withdrawn when ripe from the ground; but
should this be the case kindly inform me; if I do not hear I shall
understand that [the] pods ripen and are left permanently beneath the
ground.

If you ever come across heliotropic or apheliotropic aerial roots on a
plant not valuable (but which should be returned), I should like to
observe them. Bignonia capreolata, with its strongly apheliotropic
tendrils (which I had from Kew), is now interesting me greatly. Veitch
tells me it is not on sale in any London nursery, as I applied to him
for some additional plants. So much for business.

I have received from the Geographical Soc. your lecture, and read it
with great interest. (747/2. "On Plant-Distribution as a field for
Geographical Research." "Geog. Soc. Proc." XXII., 1878, page 412.) But
it ought not merely to be read; it requires study. The sole criticism
which I have to make is that parts are too much condensed: but, good
Lord, how rare a fault is this! You do not quote Saporta, I think; and
some of his work on the Tertiary plants would have been useful to you.
In a former note you spoke contemptuously of your lecture: all I can
say is that I never heard any one speak more unjustly and shamefully of
another than you have done of yourself!

LETTER 748. TO H. MULLER.
Down, September 20th, 1878.

I am working away on some points in vegetable physiology, but though
they interest me and my son, yet they have none of the fascination which
the fertilisation of flowers possesses. Nothing in my life has ever
interested me more than the fertilisation of such plants as Primula and
Lythrum, or again Anacamptis (748/1. Orchis pyramidalis.) or Listera.

LETTER 749. TO H. MULLER.
Down, February 12th [1879].

I have just heard that some misfortune has befallen you, and that you
have been treated shamefully. (749/1. Hermann Muller was accused by
the Ultramontane party of introducing into his school-teaching crude
hypotheses ("unreife Hypothesen"), which were assumed to have a harmful
influence upon the religious sentiments of his pupils. Attempts were
made to bring about Muller's dismissal, but the active hostility of his
opponents, which he met in a dignified spirit, proved futile. ("Prof.
Dr. Hermann Muller von Lippstadt. Ein Gedenkblatt," von Ernst Krause.
"Kosmos," VII., page 393, 1883.)) I grieve deeply to hear this, and as
soon as you can find a few minutes to spare, I earnestly beg you to let
me hear what has happened.