More Letters of Charles Darwin Volume II

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I hear from Frank that you think that the absence of both lateral
leaflets, or of one alone, is due to their having dropped off; I thought
so at first, and examined extremely young leaves from the tips of the
shoots, and some of them presented the same characters. Some
appearances make me think that they abort by becoming confluent with the
main petiole.

I hear also that you doubt about the little leaflets ever standing not
opposite to each other: pray look at the enclosed old leaf which has
been for a time in spirits, and can you call the little leaflets
opposite? I have seen many such cases on both my plants, though few so
well marked.

LETTER 719. TO J.D. HOOKER.
Down, October 23rd [1873].

How good you have been about the plants; but indeed I did not intend you
to write about Drosophyllum, though I shall be very glad to have a
specimen. Experiments on other plants lead to fresh experiments.
Neptunia is evidently a hopeless case. I shall be very glad of the
other plants whenever they are ready. I constantly fear that I shall
become to you a giant of bores.

I am delighted to hear that you are at work on Nepenthes, and I hope
that you will have good luck. It is good news that the fluid is acid;
you ought to collect a good lot and have the acid analysed. I hope that
the work will give you as much pleasure as analogous work has me.
(719/1. Hooker's work on Nepenthes is referred to in "Insectivorous
Plants," page 97: see also his address at the Belfast meeting of the
British Association, 1874.) I do not think any discovery gave me more
pleasure than proving a true act of digestion in Drosera.

LETTER 720. TO J.D. HOOKER.
Down, November 24th, 1873.

I have been greatly interested by Mimosa albida, on which I have been
working hard. Whilst your memory is pretty fresh, I want to ask a
question. When this plant was most sensitive, and you irritated it, did
the opposite leaflets shut up quite close, as occurs during sleep, when
even a lancet could not be inserted between the leaflets? I can never
cause the leaflets to come into contact, and some reasons make me doubt
whether they ever do so except during sleep; and this makes me wish much
to hear from you. I grieve to say that the plant looks more unhealthy,
even, than it was at Kew. I have nursed it like the tenderest infant;
but I was forced to cut off one leaf to try the bloom, and one was
broken by the manner of packing. I have never syringed (with tepid
water) more than one leaf per day; but if it dies, I shall feel like a
murderer. I am pretty well convinced that I shall make out my case of
movements as a protection against rain lodging on the leaves. As far as
I have as yet made out, M. albida is a splendid case.

I have had no time to examine more than one species of Eucalyptus. The
seedlings of Lathyrus nissolia are very interesting to me; and there is
something wonderful about them, unless seeds of two distinct leguminous
species have got somehow mingled together.

LETTER 721. TO W. THISELTON-DYER.
Down, December 4th, 1873.

As Hooker is so busy, I should be very much obliged if you could give me
the name of the enclosed poor specimen of Cassia. I want much to know
its name, as its power of movement, when it goes to sleep, is very
remarkable. Linnaeus, I find, was aware of this. It twists each
separate leaflet almost completely round (721/1. See "Power of Movement
in Plants," Figure 154, page 370.), so that the lower surface faces the
sky, at the same time depressing them all. The terminal leaflets are
pointed towards the base of the leaf. The whole leaf is also raised up
about 12 deg. When I saw that it possessed such complex powers of
movement, I thought it would utilise its power to protect the leaflets
from rain. Accordingly I syringed the plant for two minutes, and it was
really beautiful to see how each leaflet on the younger leaves twisted
its short sub-petiole, so that the blade was immediately directed at an
angle between 45 and 90 deg to the horizon. I could not resist the
pleasure of just telling you why I want to know the name of the Cassia.
I should add that it is a greenhouse plant. I suppose that there will
not be any better flowers till next summer or autumn.

LETTER 722. TO T. BELT.

(722/1. Belt's account, discussed in this letter, is probably that
published in his "Naturalist in Nicaragua" (1874), where he describes
"the relation between the presence of honey-secreting glands on plants,
and the protection to the latter secured by the attendance of ants
attracted by the honey." (Op. cit., pages 222 et seq.))

Thursday [1874?].

Your account of the ants and their relations seems to me to possess
extraordinary interest. I do not doubt that the excretion of sweet
fluid by the glands is in your cases of great advantage to the plants by
means of the ants, but I cannot avoid believing that primordially it is
a simple excretion, as occasionally occurs from the surface of the
leaves of lime trees. It is quite possible that the primordial
excretion may have been beneficially increased to serve the plant. In
the common laurel [Prunus laurocerasus] of our gardens the hive-bees
visit incessantly the glands of the young leaves, on their under sides;
and I should altogether doubt whether their visits or the occasional
visits of ants was of any service to the laurel. The stipules of the
common vetch secrete largely during sunshine, and hive-bees collect the
sweet fluid. So I think it is with the common bean.

I am writing this away from home, and I have come away to get some rest,
having been a good deal overworked. I shall read your book with great
interest when published, but will not trouble you to send the MS., as I
really have no spare strength or time. I believe that your book,
judging by the chapter sent, will be extremely valuable.

LETTER 723. TO J.D. HOOKER.

(723/1. The following letter refers to Darwin's prediction as to the
manner in which Hedychium (Zinziberaceae) is fertilised. Sir J.D.
Hooker seems to have made inquiries in India in consequence of which
Darwin received specimens of the moth which there visits the flower,
unfortunately so much broken as to be useless (see "Life and Letters,"
III., page 284).)

Down, March 25th [1874].

I am glad to hear about the Hedychium, and how soon you have got an
answer! I hope that the wings of the Sphinx will hereafter prove to be
bedaubed with pollen, for the case will then prove a fine bit of
prophecy from the structure of a flower to special and new means of
fertilisation.

By the way, I suppose you have noticed what a grand appearance the plant
makes when the green capsules open, and display the orange and crimson
seeds and interior, so as to attract birds, like the pale buff flowers
to attract dusk-flying lepidoptera. I presume you do not want seeds of
this plant, as I have plenty from artificial fertilisation.

(723/2. In "Nature," June 22nd, 1876, page 173, Hermann Muller
communicated F. Muller's observation on the fertilisation of a
bright-red-flowered species of Hedychium, which is visited by
Callidryas, chiefly the males of C. Philea. The pollen is carried by
the tips of the butterfly's wing, to which it is temporarily fixed by
the slimy layer produced by the degeneration of the anther-wall.

LETTER 724. TO W. THISELTON-DYER.
Down, June 4th [1874].

I am greatly obliged to you about the Opuntia, and shall be glad if you
can remember Catalpa. I wish some facts on the action of water, because
I have been so surprised at a stream not acting on Dionoea and Drosera.
(724/1. See Pfeffer, "Untersuchungen Bot. Inst. zu Tubingen," Bd. I.,
1885, page 518. Pfeffer shows that in some cases--Drosera, for
instance--water produces movement only when it contains fine particles
in suspension. According to Pfeffer the stamens of Berberis, and the
stigma of Mimulus, are both stimulated by gelatine, the action of which
is, generally speaking, equivalent to that of water.) Water does not
act on the stamens of Berberis, but it does on the stigma of Mimulus.
It causes the flowers of the bedding-out Mesembryanthemum and Drosera to
close, but it has not this effect on Gazania and the daisy, so I can
make out no rule.

I hope you are going on with Nepenthes; and if so, you will perhaps like
to hear that I have just found out that Pinguicula can digest albumen,
gelatine, etc. If a bit of glass or wood is placed on a leaf, the
secretion is not increased; but if an insect or animal-matter is thus
placed, the secretion is greatly increased and becomes feebly acid,
which was not the case before. I have been astonished and much
disturbed by finding that cabbage seeds excite a copious secretion, and
am now endeavouring to discover what this means. (724/2. Clearly it
had not occurred to Darwin that seeds may supply nitrogenous food as
well as insects: see "Insectivorous Plants," page 390.) Probably in a
few days' time I shall have to beg a little information from you, so I
will write no more now.

P.S. I heard from Asa Gray a week ago, and he tells me a beautiful
fact: not only does the lid of Sarracenia secrete a sweet fluid, but
there is a line or trail of sweet exudation down to the ground so as to
tempt insects up. (724/3. A dried specimen of Sarracenia, stuffed with
cotton wool, was sometimes brought from his study by Mr. Darwin, and
made the subject of a little lecture to visitors of natural history
tastes.)

LETTER 725. TO W. THISELTON-DYER.
Down, June 23rd, 1874.

I wrote to you about a week ago, thanking you for information on cabbage
seeds, asking you the name of Luzula or Carex, and on some other points;
and I hope before very long to receive an answer. You must now, if you
can, forgive me for being very troublesome, for I am in that state in
which I would sacrifice friend or foe. I have ascertained that bits of
certain leaves, for instance spinach, excite much secretion in
Pinguicula, and that the glands absorb matter from the leaves. Now this
morning I have received a lot of leaves from my future daughter-in-law
in North Wales, having a surprising number of captured insects on them,
a good many leaves, and two seed-capsules. She informs me that the
little leaves had excited secretion; and my son and I have ascertained
this morning that the protoplasm in the glands beneath the little leaves
has undoubtedly undergone aggregation. Therefore, absurd as it may
sound, I am prepared to affirm that Pinguicula is not only
insectivorous, but graminivorous, and granivorous! Now I want to beg
you to look under the simple microscope at the enclosed leaves and
seeds, and, if you possibly can, tell me their genera. The little
narrow leaves are remarkable (725/1. Those of Erica tetralix.); they
are fleshy, with the edges much curled from the axis of the plant, and
bear a few long glandular hairs; these grow in little tufts. These are
the commonest in Pinguicula, and seem to afford most nutritious matter.
A second leaf is like a miniature sycamore. With respect to the seeds,
I suppose that one is a Carex; the other looks like that of Rumex, but
is enclosed in a globular capsule. The Pinguicula grew on marshy, low,
mountainous land.

I hope you will think this subject sufficiently interesting to make you
willing to aid me as far as you can. Anyhow, forgive me for being so
very troublesome.

LETTER 726. TO J.D. HOOKER.
Down, August 30th [1874].

I am particularly obliged for your address. (726/1. Presidential
address (Biological Section) at the Belfast meeting of the British
Association, 1874.) It strikes me as quite excellent, and has
interested me in the highest degree. Nor is this due to my having
worked at the subject, for I feel sure that I should have been just as
much struck, perhaps more so, if I had known nothing about it. You
could not, in my opinion, have put the case better. There are several
lights (besides the facts) in your essay new to me, and you have greatly
honoured me. I heartily congratulate you on so splendid a piece of
work. There is a misprint at page 7, Mitschke for Nitschke. There is a
partial error at page 8, where you say that Drosera is nearly
indifferent to organic substances. This is much too strong, though they
do act less efficiently than organic with soluble nitrogenous matter;
but the chief difference is in the widely different period of subsequent
re-expansion. Thirdly, I did not suggest to Sanderson his electrical
experiments, though, no doubt, my remarks led to his thinking of them.

Now for your letter: you are very generous about Dionoea, but some of
my experiments will require cutting off leaves, and therefore injuring
plants. I could not write to Lady Dorothy [Nevill]. Rollisson says
that they expect soon a lot from America. If Dionoea is not despatched,
have marked on address, "to be forwarded by foot-messenger."

Mrs. Barber's paper is very curious, and ought to be published (726/2.
Mrs. Barber's paper on the pupa of Papilio Nireus assuming different
tints corresponding to the objects to which it was attached, was
communicated by Mr. Darwin to the "Trans. Entomolog. Soc." 1874.); but
when you come here (and REMEMBER YOU OFFERED TO COME) we will consult
where to send it. Let me hear when you recommence on Cephalotus or
Sarracenia, as I think I am now on right track about Utricularia, after
wasting several weeks in fruitless trials and observations. The
negative work takes five times more time than the positive.

LETTER 727. TO J.D. HOOKER.
Down, September 18th [1874].

I have had a splendid day's work, and must tell you about it.

Lady Dorothy sent me a young plant of U[tricularia] montana (727/1. See
"Life and Letters," III., page 327, and "Insectivorous Plants," page
431.), which I fancy is the species you told me of. The roots or
rhizomes (for I know not which they are; I can see no scales or
internodes or absorbent hairs) bear scores of bladders from 1/20 to
1/100 of an inch in diameter; and I traced these roots to the depth of 1
1/2 in. in the peat and sand. The bladders are like glass, and have the
same essential structure as those of our species, with the exception
that many exterior parts are aborted. Internally the structure is
perfect, as is the minute valvular opening into the bladder, which is
filled with water. I then felt sure that they captured subterranean
insects, and after a time I found two with decayed remnants, with clear
proof that something had been absorbed, which had generated protoplasm.
When you are here I shall be very curious to know whether they are roots
or rhizomes.

Besides the bladders there are great tuber-like swellings on the
rhizomes; one was an inch in length and half in breadth. I suppose
these must have been described. I strongly suspect that they serve as
reservoirs for water. (727/2. The existence of water-stores is quite in
accordance with the epiphytic habit of the plant.) But I shall
experimentise on this head. A thin slice is a beautiful object, and
looks like coarsely reticulated glass.

If you have an old plant which could be turned out of its pot (and can
spare the time), it would be a great gain to me if you would tear off a
bit of the roots near the bottom, and shake them well in water, and see
whether they bear these minute glass-like bladders. I should also much
like to know whether old plants bear the solid bladder-like bodies near
the upper surface of the pot. These bodies are evidently enlargements
of the roots or rhizomes. You must forgive this long letter, and make
allowance for my delight at finding this new sub-group of
insect-catchers. Sir E. Tennent speaks of an aquatic species of
Utricularia in Ceylon, which has bladders on its roots, and rises
annually to the surface, as he says, by this means. (727/3.
Utricularia stellaris. Emerson Tennent's "Ceylon," Volume I., page 124,
1859.)

We shall be delighted to see you here on the 26th; if you will let us
know your train we will send to meet you. You will have to work like a
slave while you are here.

LETTER 728. TO J. JENNER WEIR.

(728/1. In 1870 Mr. Jenner Weir wrote to Darwin: "My brother has but
two kinds of laburnum, viz., Cytisus purpureus, very erect, and Cytisus
alpinus, very pendulous. He has several stocks of the latter grafted
with the purple one; and this year, the grafts being two years old, I
saw in one, fairly above the stock, about four inches, a raceme of
purely yellow flowers with the usual dark markings, and above them a
bunch of purely purple flowers; the branches of the graft in no way
showed an intermediate character, but had the usual rigid growth of
purpureus."

Early in July 1875, when Darwin was correcting a new edition of
"Variation under Domestication," he again corresponded with Mr. Weir on
the subject.)

Down, July 8th [1875].

I thank you cordially. The case interests me in a higher degree than
anything which I have heard for a very long time. Is it your brother
Harrison W., whom I know? I should like to hear where the garden is.
There is one other very important point which I am most anxious to
hear--viz., the nature of the leaves at the base of the yellow racemes,
for leaves are always there produced with the yellow laburnums, and I
suppose so in the case of C. purpureus. As the tree has produced yellow
racemes several times, do you think you could ask your brother to cut
off and send me by post in a box a small branch of the purple stock with
the pods or leaves of the yellow sport? (728/2. "The purple stock"
here means the supposed C. purpureus, on which a yellow-flowered branch
was borne.) This would be an immense favour, for then I would cut the
point of junction longitudinally and examine slice under the microscope,
to be able to state no trace of bud of yellow kind having been inserted.
I do not suspect anything of the kind, but it is sure to be said that
your brother's gardener, either by accident or fraud, inserted a bud.
Under this point of view it would be very good to gather from your
brother how many times the yellow sport has appeared. The case appears
to me so very important as to be worth any trouble. Very many thanks
for all assistance so kindly given.

I will of course send a copy of new edition of "Variation under
Domestication" when published in the autumn.

LETTER 729. TO J. JENNER WEIR.

(729/1. On July 9th Mr. Weir wrote to say that a branch of the Cytisus
had been despatched to Down. The present letter was doubtless written
after Darwin had examined the specimen. In "Variation under
Domestication," Edition II., Volume I., page 417, note, he gives for a
case recorded in the "Gardeners' Chronicle" in 1857 the explanation here
offered (viz. that the graft was not C. purpureus but C. Adami), and
adds, "I have ascertained that this occurred in another instance." This
second instance is doubtless Mr. Weir's.)

Down, July 10th, 1875.

I do not know how to thank you enough; pray give also my thanks and kind
remembrances to your brother. I am sure you will forgive my expressing
my doubts freely, as I well know that you desire the truth more than
anything else. I cannot avoid the belief that some nurseryman has sold
C[ytisus] Adami to your brother in place of the true C. purpureus. The
latter is a little bush only 3 feet high (Loudon), and when I read your
account, it seemed to me a physical impossibility that a sporting branch
of C. alpinus could grow to any size and be supported on the extremely
delicate branches of C. purpureus. If I understand rightly your letter,
you consider the tuft of small shoots on one side of the sporting C.
alpinus from Weirleigh as C. purpureus; but these shoots are certainly
those of C. Adami. I earnestly beg you to look at the specimens
enclosed. The branch of the true C. purpureus is the largest which I
could find. If C. Adami was sold to your brother as C. purpureus,
everything is explained; for then the gardener has grafted C. Adami on
C. alpinus, and the former has sported in the usual manner; but has not
sported into C. purpureus, only into C. alpinus. C. Adami does not
sport less frequently into C. purpureus than into C. alpinus. Are the
purple flowers borne on moderately long racemes? If so, the plant is
certainly C. Adami, for the true C. purpureus bears flowers close to the
branches. I am very sorry to be so troublesome, but I am very anxious
to hear again from you.

C. purpureus bears "flowers axillary, solitary, stalked."

P.S.--I think you said that the purple [tree] at Weirleigh does not
seed, whereas the C. purpureus seeds freely, as you may see in enclosed.
C. Adami never produces seeds or pods.

LETTER 730. TO E. HACKEL.

(730/1. The following extract refers to Darwin's book on "Cross and
Self-Fertilisation.")

November 13th, 1875.

I am now busy in drawing up an account of ten years' experiments in the
growth and fertility of plants raised from crossed and self-fertilised
flowers. It is really wonderful what an effect pollen from a distinct
seedling plant, which has been exposed to different conditions of life,
has on the offspring in comparison with pollen from the same flower or
from a distinct individual, but which has been long subjected to the
same conditions. The subject bears on the very principle of life, which
seems almost to require changes in the conditions.

LETTER 731. TO G.J. ROMANES.

(731/1. The following extract from a letter to Romanes refers to
Francis Darwin's paper, "Experiments on the Nutrition of Drosera
rotundifolia." "Linn. Soc. Journ." [1878], published 1880, page 17.)

August 9th [1876].

The second point which delights me, seeing that half a score of
botanists throughout Europe have published that the digestion of meat by
plants is of no use to them (a mere pathological phenomenon, as one man
says!), is that Frank has been feeding under exactly similar conditions
a large number of plants of Drosera, and the effect is wonderful. On
the fed side the leaves are much larger, differently coloured, and more
numerous; flower-stalks taller and more numerous, and I believe far more
seed capsules,--but these not yet counted. It is particularly
interesting that the leaves fed on meat contain very many more starch
granules (no doubt owing to more protoplasm being first formed); so that
sections stained with iodine, of fed and unfed leaves, are to the naked
eye of very different colours.

There, I have boasted to my heart's content, and do you do the same, and
tell me what you have been doing.

LETTER 732. TO J.D. HOOKER.
Down, October 25th [1876].

If you can put the following request into any one's hands pray do so;
but if not, ignore my request, as I know how busy you are.

I want any and all plants of Hoya examined to see if any imperfect
flowers like the one enclosed can be found, and if so to send them to
me, per post, damp. But I especially want them as young as possible.

They are very curious. I have examined some sent me from Abinger
(732/1. Lord Farrer's house.), but they were a month or two too old,
and every trace of pollen and anthers had disappeared or had never been
developed. Yet a very fine pod with apparently good seed had been
formed by one such flower. (732/2. The seeds did not germinate; see
the account of Hoya carnosa in "Forms of Flowers," page 331.)

LETTER 733. TO G.J. ROMANES.

(733/1. Published in the "Life of Romanes," page 62.)

Down, August 10th [1877].

When I went yesterday I had not received to-day's "Nature," and I
thought that your lecture was finished. (733/2. Abstract of a lecture
on "Evolution of Nerves and Nervo-Systems," delivered at the Royal
Institution, May 25th, 1877. "Nature," July 19th, August 2nd, August
9th, 1877.) This final part is one of the grandest essays which I ever
read.

It was very foolish of me to demur to your lines of conveyance like the
threads in muslin (733/3. "Nature," August 2nd, page 271.), knowing how
you have considered the subject: but still I must confess I cannot feel
quite easy. Everyone, I suppose, thinks on what he has himself seen,
and with Drosera, a bit of meat put on any one gland on its disc causes
all the surrounding tentacles to bend to this point, and here there can
hardly be differentiated lines of conveyance. It seems to me that the
tentacles probably bend to that point wherever a molecular wave strikes
them, which passes through the cellular tissue with equal ease in all
directions in this particular case. (733/4. Speaking generally, the
transmission takes place more readily in the longitudinal direction than
across the leaf: see "Insectivorous Plants," page 239.) But what a
fine case that of the Aurelia is! (733/5. Aurelia aurita, one of the
medusae. "Nature," pages 269-71.)

LETTER 734. TO W. THISELTON-DYER.
6, Queen Anne Street [December 1876].

Tell Hooker I feel greatly aggrieved by him: I went to the Royal
Society to see him for once in the chair of the Royal, to admire his
dignity and enjoy it, and lo and behold, he was not there. My outing
gave me much satisfaction, and I was particularly glad to see Mr.
Bentham, and to see him looking so wonderfully well and young. I saw
lots of people, and it has not done me a penny's worth of harm, though I
could not get to sleep till nearly four o'clock.