Чарльз Дарвин
More Letters of Charles Darwin — Volume 2
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.
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.
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."
