It was very kind of you to send me two numbers of the "Gardeners'

Chronicle" with your two articles, which I have read with much interest.

(753/1. "Gardeners' Chronicle," 1879, page 652; 1880, pages 108, 173.) You have quite convinced me, whatever Mr. Asher may say to the contrary.

I want to ask you a question, on the bare chance of your being able to answer it, but if you cannot, please do not take the trouble to write.

The lateral branches of the silver fir often grow out into k.n.o.bs through the action of a fungus, Aecidium; and from these k.n.o.bs shoots grow vertically (753/2. The well-known "Witches-Brooms," or "Hexen-Besen,"

produced by the fungus Aecidium elatinum.) instead of horizontally, like all the other twigs on the same branch. Now the roots of Cruciferae and probably other plants are said to become k.n.o.bbed through the action of a fungus: now, do these k.n.o.bs give rise to rootlets? and, if so, do they grow in a new or abnormal direction? (753/3. The parasite is probably Plasmodiophora: in this case no abnormal rootlets have been observed, as far as we know.)

LETTER 754. TO W. THISELTON-DYER. Down, June 18th, 1879.

The plants arrived last night in first-rate order, and it was very very good of you to take so much trouble as to hunt them up yourself. They seem exactly what I wanted, and if I fail it will not be for want of perfect materials. But a confounded painter (I beg his pardon) comes here to-night, and for the next two days I shall be half dead with sitting to him; but after then I will begin to work at the plants and see what I can do, and very curious I am about the results.

I have to thank you for two very interesting letters. I am delighted to hear, and with surprise, that you care about old Erasmus D. G.o.d only knows what I shall make of his life--it is such new kind of work to me.

(754/1. "Erasmus Darwin." By Ernst Krause. Translated from the German by W.S. Dallas: with a preliminary notice by Charles Darwin. London, 1879.

See "Life and Letters," III., pages 218-20.)

Thanks for case of sleeping Crotalaria--new to me. I quite agree to every word you say about Ball's lecture (754/2. "On the Origin of the Flora of the European Alps," "Geogr. Soc. Proc." Volume I., 1879, page 564. See Letter 395, Volume II.)--it is, as you say, like Sir W.

Thomson's meteorite. (754/3. In 1871 Lord Kelvin (Presidential Address Brit. a.s.soc.) suggested that meteorites, "the moss-grown fragments from the ruins of another world," might have introduced life to our planet.) It is really a pity; it is enough to make Geographical Distribution ridiculous in the eyes of the world. Frank will be interested about the Auriculas; I never attended to this plant, for the powder did [not] seem to me like true "bloom." (754/4. See Francis Darwin, on the relation between "bloom" on leaves and the distribution of the stomata. "Linn.

Soc. Journ." Volume XXII., page 114.) This subject, however, for the present only, has gone to the dogs with me.

I am sorry to hear of such a struggle for existence at Kew; but I have often wondered how it is that you are all not killed outright.

I can most fully sympathise with you in your admiration of your little girl. There is nothing so charming in this world, and we all in this house humbly adore our grandchild, and think his little pimple of a nose quite beautiful.

LETTER 755. TO G. BENTHAM. Down, February 16th, 1880.

I have had real pleasure in signing Dyer's certificate. (755/1. As a candidate for the Royal Society.) It was very kind in you to write to me about the Orchideae, for it has pleased me to an extreme degree that I could have been of the least use to you about the nature of the parts.

They are wonderful creatures, these orchids, and I sometimes think with a glow of pleasure, when I remember making out some little point in their method of fertilisation. (755/2. Published in "Life and Letters,"

III., page 288.) With respect to terms, no doubt you will be able to improve them greatly, for I knew nothing about the terms as used in other groups of plants. Could you not invent some quite new term for gland, implying viscidity? or append some word to gland. I used for cirripedes "cement gland."

Your present work must be frightfully difficult. I looked at a few dried flowers, and could make neither heads nor tails of them; and I well remember wondering what you would do with them when you came to the group in the "Genera Plantarum." I heartily wish you safe through your work,...

LETTER 756. TO F.M. BALFOUR. Down, September 4th, 1880.

I hope that you will not think me a great bore, but I have this minute finished reading your address at the British a.s.sociation; and it has interested me so much that I cannot resist thanking you heartily for the pleasure derived from it, not to mention the honour which you have done me. (756/1. Presidential address delivered by Prof. F.M. Balfour before the Biological Section at the British a.s.sociation meeting at Swansea (1880).) The recent progress of embryology is indeed splendid. I have been very stupid not to have hitherto read your book, but I have had of late no spare time; I have now ordered it, and your address will make it the more interesting to read, though I fear that my want of knowledge will make parts unintelligible to me. (756/2. "A Treatise on Comparative Embryology," 2 volumes. London, 1880.) In my recent work on plants I have been astonished to find to how many very different stimuli the same small part--viz., the tip of the radicle--is sensitive, and has the power of transmitting some influence to the adjoining part of the radicle, exciting it to bend to or from the source of irritation according to the needs of the plant (756/3. See Letter 757.); and all this takes place without any nervous system! I think that such facts should be kept in mind when speculating on the genesis of the nervous system. I always feel a malicious pleasure when a priori conclusions are knocked on the head: and therefore I felt somewhat like a devil when I read your remarks on Herbert Spencer (756/4. Prof. Balfour discussed Mr. Herbert Spencer's views on the genesis of the nervous system, and expressed the opinion that his hypothesis was not borne out by recent discoveries. "The discovery that nerves have been developed from processes of epithelial cells gives a very different conception of their genesis to that of Herbert Spencer, which makes them originate from the pa.s.sage of nervous impulses through a track of mingled colloids..."

(loc. cit., page 644.))...Our recent visit to Cambridge was a brilliant success to us all, and will ever be remembered by me with much pleasure.

LETTER 757. TO JAMES PAGET.

(757/1. During the closing years of his life, Darwin began to experimentise on the possibility of producing galls artificially. A letter to Sir J.D. Hooker (November 3rd, 1880) shows the interest which he felt in the question:--

"I was delighted with Paget's essay (757/2. An address on "Elemental Pathology," delivered before the British Medical a.s.sociation, August 1880, and published in the Journal of the a.s.sociation.); I hear that he has occasionally attended to this subject from his youth...I am very glad he has called attention to galls: this has always seemed to me a profoundly interesting subject; and if I had been younger would take it up."

His interest in this subject was connected with his ever-present wish to learn something of the causes of variation. He imagined to himself wonderful galls caused to appear on the ovaries of plants, and by these means he thought it possible that the seed might be influenced, and thus new varieties arise. (757/3. There would have been great difficulties about this line of research, for when the s.e.xual organs of plants are deformed by parasites (in the way he hoped to effect by poisons) sterility almost always results. See Molliard's "Les Cecidies Florales,"

"Ann. Sci. Nat." 1895, Volume I., page 228.) He made a considerable number of experiments by injecting various reagents into the tissues of leaves, and with some slight indications of success. (757/4. The above pa.s.sage is reprinted, with alterations, from "Life and Letters," III., page 346.)

The following letter to the late Sir James Paget refers to the same subject.)

Down, November 14th, 1880.

I am very much obliged for your essay, which has interested me greatly.

What indomitable activity you have! It is a surprising thought that the diseases of plants should ill.u.s.trate human pathology. I have the German "Encyclopaedia," and a few weeks ago told my son Francis that the article on the diseases of plants would be well worth his study; but I did not know it was written by Dr. Frank, for whom I entertain a high respect as a first-rate observer and experimentiser, though for some unknown reason he has been a good deal snubbed in Germany. I can give you one good case of regrowth in plants, recently often observed by me, though only externally, as I do not know enough of histology to follow out details. It is the tip of the radicle of a germinating common bean.

The case is remarkable in some respects, for the tip is sensitive to various stimuli, and transmits an order, causing the upper part of the radicle to bend. When the tip (for a length of about 1 mm.) is cut transversely off, the radicle is not acted on by gravitation or other irritants, such as contact, etc., etc., but a new tip is regenerated in from two to four days, and then the radicle is again acted on by gravitation, and will bend to the centre of the earth. The tip of the radicle is a kind of brain to the whole growing part of the radicle!

(757/5. We are indebted to Mr. Archer-Hind for the translation of the following pa.s.sage from Plato ("Timaeus," 90A): "The reason is every man's guardian genius (daimon), and has its habitation in our brain; it is this that raises man (who is a plant, not of earth but of heaven) to an erect posture, suspending the head and root of us from the heavens, which are the birthplace of our soul, and keeping all the body upright."

On the perceptions of plants, see "Nature," November 14th, 1901--a lecture delivered at the Glasgow meeting of the British a.s.sociation by Francis Darwin. See also Bonitz, "Index Aristotelicus," S.V. phuton.)

My observation will be published in about a week's time, and I would have sent you the book, but I do not suppose that there is anything else in the book which would interest you. I am delighted that you have drawn attention to galls. They have always seemed to me profoundly interesting. Many years ago I began (but failed for want of time, strength, and health, as on infinitely many other occasions) to experimentise on plants, by injecting into their tissues some alkaloids and the poison of wasps, to see if I could make anything like galls.

If I remember rightly, in a few cases the tissues were thickened and hardened. I began these experiments because if by different poisons I could have affected slightly and differently the tissues of the same plant, I thought there would be no insuperable difficulty in the fittest poisons being developed by insects so as to produce galls adapted for them. Every character, as far as I can see, is apt to vary. Judging from one of your sentences you will smile at this.

To any one believing in my pangenesis (if such a man exists) there does not seem to me any extreme difficulty in understanding why plants have such little power of regeneration; for there is reason to think that my imaginary gemmules have small power of pa.s.sing from cell to cell.

(757/6. On regeneration after injury, see Ma.s.sart, "La Cicatrisation chez les Vegetaux," in Volume 57 (1898) of the "Memoires Couronnes,"

published by the Royal Academy of Belgium. An account of the literature is given by the author.)

Forgive me for scribbling at such unreasonable length; but you are to blame for having interested me so much.

P.S.--Perhaps you may remember that some two years ago you asked me to lunch with you, and proposed that I should offer myself again. Whenever I next come to London, I will do so, and thus have the pleasure of seeing you.

LETTER 758. TO W. THISELTON-DYER.

(758/1. "The Power of Movement in Plants" was published early in November, 1880. Sir W. Thiselton-Dyer, in writing to thank Darwin for a copy of the book, had (November 20th) compared a structure in the seedling Welwitschia with the "peg" of Cucurbita (see "Power of Movement," page 102). Dyer wrote: "One peculiar feature in the germinating embryo is a lateral hypocotyledonary process, which eventually serves as an absorbent organ, by which the nutriment of the endosperm is conveyed to the seedling. Such a structure was quite new to me, and Bower and I were disposed to see in it a representative of the foot in Selaginella, when I saw the account of Flahault's 'peg.'"

Flahault, it should be explained, was the discoverer of the curious peg in Cucurbita. Prof. Bower wrote a paper ("On the Germination and Histology of the seedling of Welwitschia mirabilis" in the "Quart.

Journ. Microscop. Sci." XXI., 1881, page 15.)

Down, November 28th [1880].

Very many thanks for your most kind note, but you think too highly of our work--not but what this is very pleasant.

I am deeply interested about Welwitschia. When at work on the pegs or projections I could not imagine how they were first developed, before they could have been of mere mechanical use. Now it seems possible that a circle between radicle and hypocotyl may be permeable to fluids, and thus have given rise to projections so as to expose larger surface.

Could you test Welwitschia with permanganate of pota.s.sium: if, like my pegs, the lower surface would be coloured brown like radicle, and upper surface left white like hypocotyl. If such an idea as yours, of an absorbing organ, had ever crossed my mind, I would have tried many hypocotyls in weak citrate of ammonia, to see if it penetrated on line of junction more easily than elsewhere. I daresay the projection in Abronia and Mirabilis may be an absorbent organ. It was very good fun bothering the seeds of Cucurbita by planting them edgeways, as would never naturally occur, and then the peg could not act properly. Many of the Germans are very contemptuous about making out use of organs; but they may sneer the souls out of their bodies, and I for one shall think it the most interesting part of natural history. Indeed, you are greatly mistaken if you doubt for one moment on the very great value of your constant and most kind a.s.sistance to us. I have not seen the pamphlet, and shall be very glad to keep it. Frank, when he comes home, will be much interested and pleased with your letter. Pray give my kindest remembrance to Mrs. Dyer.

This is a very untidy note, but I am very tired with dissecting worms all day. Read the last chapter of our book, and then you will know the whole contents.

LETTER 759. TO H. VOCHTING. Down, December 16th, 1880.

Absence from home has prevented me from sooner thanking you for your kind present of your several publications. I procured some time ago your "Organbilding" (759/1. "Organbildung im Pflanzenreich," 1878.) etc., but it was too late for me to profit by it for my book, as I was correcting the press. I read only parts, but my son Francis read the whole with care and told me much about it, which greatly interested me. I also read your article in the "Bot. Zeitung." My son began at once experimenting, to test your views, and this very night will read a paper before the Linnean Society on the roots of Rubus (759/2. Francis Darwin, "The Theory of the Growth of Cuttings" ("Linn. Soc. Journ." XVIII.). [I take this opportunity of expressing my regret that at page 417, owing to neglect of part of Vochting's facts, I made a criticism of his argument which cannot be upheld.--F.D.].), and I think that you will be pleased to find how well his conclusions agree with yours. He will of course send you a copy of his paper when it is printed. I have sent him your letter, which will please him if he agrees with me; for your letter has given me real pleasure, and I did not at all know what the many great physiologists of Germany, Switzerland, and Holland would think of it ["The Power of Movement," etc.]. I was quite sorry to read Sachs' views about root-forming matter, etc., for I have an unbounded admiration for Sachs. In this country we are dreadfully behind in Physiological Botany.

LETTER 760. TO A. DE CANDOLLE. Down, January 24th, 1881.

It was extremely kind of you to write me so long and valuable a letter, the whole of which deserves careful consideration. I have been particularly pleased at what you say about the new terms used, because I have often been annoyed at the mult.i.tude of new terms lately invented in all branches of Biology in Germany; and I doubted much whether I was not quite as great a sinner as those whom I have blamed. When I read your remarks on the word "purpose" in your "Phytographie," I vowed that I would not use it again; but it is not easy to cure oneself of a vicious habit. It is also difficult for any one who tries to make out the use of a structure to avoid the word purpose. I see that I have probably gone beyond my depth in discussing plurifoliate and unifoliate leaves; but in such a case as that of Mimosa albida, where rudiments of additional leaflets are present, we must believe that they were well developed in the progenitor of the plant. So again, when the first true leaf differs widely in shape from the older leaves, and resembles the older leaves in allied species, is it not the most simple explanation that such leaves have retained their ancient character, as in the case of the embryos of so many animals?

Your suggestion of examining the movements of vertical leaves with an equal number of stomata on both sides, with reference to the light, seems to me an excellent one, and I hope that my son Francis may follow it up. But I will not trouble you with any more remarks about our book.

My son will write to you about the diagram.

Let me add that I shall ever remember with pleasure your visit here last autumn.