More Letters of Charles Darwin — Volume 2

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.

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}.