More Letters of Charles Darwin — Volume 1

I am so very glad that you intend to work out the north range of the 321 European species; for it seems to me the by far most important element in their distribution.

And I am equally glad that you intend to work out range of species in regard to size of genera — i.e. number of species in genus. I have been attempting to do this in a very few cases, but it is folly for any one but a botanist to attempt it. I must think that De Candolle has fallen into error in attempting to do this for orders instead of for genera — for reasons with which I will not trouble you.

LETTER 332. TO J.D. HOOKER.

(332/1. The "verdict" referred to in the following letter was Sir J.D. Hooker's opinion on Darwin's MS. on geographical distribution. The first paragraph has been already published in "Life and Letters," II., page 86.)

Down, November 4th {1856}.

I thank you more cordially than you will think probable for your note. Your verdict has been a great relief. On my honour I had no idea whether or not you would say it was (and I knew you would say it very kindly) so bad, that you would have begged me to have burnt the whole. To my own mind my MS. relieved me of some few difficulties, and the difficulties seemed to me pretty fairly stated; but I had become so bewildered with conflicting facts — evidence, reasoning and opinions — that I felt to myself that I had lost all judgment. Your general verdict is incomparably more favourable than I had anticipated.

Very many thanks for your invitation. I had made up my mind, on my poor wife's account, not to come up to next Phil. Club; but I am so much tempted by your invitation, and my poor dear wife is so good-natured about it, that I think I shall not resist — i.e., if she does not get worse. I would come to dinner at about same time as before, if that would suit you, and I do not hear to the contrary; and would go away by the early train — i.e., about 9 o'clock. I find my present work tries me a good deal, and sets my heart palpitating, so I must be careful. But I should so much like to see Henslow, and likewise meet Lindley if the fates will permit. You will see whether there will be time for any criticism in detail on my MS. before dinner: not that I am in the least hurry, for it will be months before I come again to Geographical Distribution; only I am afraid of your forgetting any remarks.

I do not know whether my very trifling observations on means of distribution are worth your reading, but it amuses me to tell them.

The seeds which the eagle had in {its} stomach for eighteen hours looked so fresh that I would have bet five to one that they would all have grown; but some kinds were ALL killed, and two oats, one canary-seed, one clover, and one beet alone came up! Now I should have not cared swearing that the beet would not have been killed, and I should have fully expected that the clover would have been. These seeds, however, were kept for three days in moist pellets, damp with gastric juice, after being ejected, which would have helped to have injured them.

Lately I have been looking, during a few walks, at excrement of small birds. I have found six kinds of seeds, which is more than I expected. Lastly, I have had a partridge with twenty-two grains of dry earth on one foot, and to my surprise a pebble as big as a tare seed; and I now understand how this is possible, for the bird scratches itself, {and the} little plumous feathers make a sort of very tenacious plaister. Think of the millions of migratory quails (332/2. See "Origin," Edition I., page 363, where the millions of migrating quails occur again.), and it would be strange if some plants have not been transported across good arms of the sea.

Talking of this, I have just read your curious Raoul Island paper. (332/3. "Linn. Soc. Journal." I., 1857.) This looks more like a case of continuous land, or perhaps of several intervening, now lost, islands than any (according to my heterodox notions) I have yet seen. The concordance of the vegetation seems so complete with New Zealand, and with that land alone.

I have read Salter's paper and can hardly stomach it. I wonder whether the lighters were ever used to carry grain and hay to ships. (332/4. Salter, "Linn. Soc. Journal," I., 1857, page 140, "On the Vitality of Seeds after prolonged Immersion in the Sea." It appears that in 1843 the mud was scraped from the bottom of the channels in Poole Harbour, and carried to shore in barges. On this mud a vegetation differing from that of the surrounding shore sprang up.)

Adios, my dear Hooker. I thank you most honestly for your assistance — assistance, by the way, now spread over some dozen years.

P.S. — Wednesday. I see from my wife's expression that she does not really much like my going, and therefore I must give up, of course, this pleasure.

If you should have anything to discuss about my MS., I see that I could get to you by about 12, and then could return by the 2.19 o'clock train, and be home by 5.30 o'clock, and thus I should get two hours' talk. But it would be a considerable exertion for me, and I would not undertake it for mere pleasure's sake, but would very gladly for my book's sake.

LETTER 333. J.D. HOOKER TO CHARLES DARWIN. November 9th, 1856.

I have finished the reading of your MS., and have been very much delighted and instructed. Your case is a most strong one, and gives me a much higher idea of change than I had previously entertained; and though, as you know, never very stubborn about unalterability of specific type, I never felt so shaky about species before.

The first half you will be able to put more clearly when you polish up. I have in several cases made pencil alterations in details as to words, etc., to enable myself to follow better, — some of it is rather stiff reading. I have a page or two of notes for discussion, many of which were answered, as I got further on with the MS., more or less fully. Your doctrine of the cooling of the Tropics is a startling one, when carried to the length of supporting plants of cold temperate regions; and I must confess that, much as I should like it, I can hardly stomach keeping the tropical genera alive in so very cool a greenhouse {pencil note by C.D., "Not so very cool, but northern ones could range further south if not opposed"}. Still I must confess that all your arguments pro may be much stronger put than you have. I am more reconciled to iceberg transport than I was, the more especially as I will give you any length of time to keep vitality in ice, and more than that, will let you transport roots that way also.

(333/1. The above letter was pinned to the following note by Mr. Darwin.)

In answer to this show from similarity of American, and European and Alpine-Arctic plants, that they have travelled enormously without any change.

As sub-arctic, temperate and tropical are all slowly marching toward the equator, the tropical will be first checked and distressed, similarly (333/2. Almost illegible.) the temperate will invade...; after the temperate can {not} advance or do not wish to advance further the arctics will be checked and will invade. The temperates will have been far longer in Tropics than sub-arctics. The sub-arctics will first have to cross temperate {zone} and then Tropics. They would penetrate among strangers, just like the many naturalised plants brought by man, from some unknown advantage. But more, for nearly all have chance of doing so.

(333/3. The point of view is more clearly given in the following letters.)

LETTER 334. TO J.D. HOOKER. Down, November 15th {1856}.

I shall not consider all your notes on my MS. for some weeks, till I have done with crossing; but I have not been able to stop myself meditating on your powerful objection to the mundane cold period (334/1. See Letter 49.), viz. that MANY-fold more of the warm-temperate species ought to have crossed the Tropics than of the sub-arctic forms. I really think that to those who deny the modification of species this would absolutely disprove my theory. But according to the notions which I am testing — viz. that species do become changed, and that time is a most important element (which I think I shall be able to show very clearly in this case) — in such change, I think, the result would be as follows. Some of the warm-temperate forms would penetrate the Tropics long before the sub-arctic, and some might get across the equator long before the sub-arctic forms could do so (i.e. always supposing that the cold came on slowly), and therefore these must have been exposed to new associates and new conditions much longer than the sub-arctic. Hence I should infer that we ought to have in the warm-temperate S. hemisphere more representative or modified forms, and fewer identical species than in comparing the colder regions of the N. and S. I have expressed this very obscurely, but you will understand, I think, what I mean. It is a parallel case (but with a greater difference) to the species of the mountains of S. Europe compared with the arctic plants, the S. European alpine species having been isolated for a longer period than on the arctic islands. Whether there are many tolerably close species in the warm-temperate lands of the S. and N. I know not; as in La Plata, Cape of Good Hope, and S. Australia compared to the North, I know not. I presume it would be very difficult to test this, but perhaps you will keep it a little before your mind, for your argument strikes me as by far the most serious difficulty which has occurred to me. All your criticisms and approvals are in simple truth invaluable to me. I fancy I am right in speaking in this note of the species in common to N. and S. as being rather sub-arctic than arctic.

This letter does not require any answer. I have written it to ease myself, and to get you just to bear your argument, under the modification point of view, in mind. I have had this morning a most cruel stab in the side on my notion of the distribution of mammals in relation to soundings.

LETTER 335. J.D. HOOKER TO CHARLES DARWIN. Kew, Sunday {November 1856}.

I write only to say that I entirely appreciate your answer to my objection on the score of the comparative rareness of Northern warm-temperate forms in the Southern hemisphere. You certainly have wriggled out of it by getting them more time to change, but as you must admit that the distance traversed is not so great as the arctics have to travel, and the extremes of modifying cause not so great as the arctics undergo, the result should be considerably modified thereby. Thus: the sub-arctics have (1) to travel twice as far, (2) taking twice the time, (3) undergoing many more disturbing influences.

All this you have to meet by giving the North temperate forms simply more time. I think this will hardly hold water.

LETTER 336. TO J.D. HOOKER. Down, November 18th {1856}.

Many thanks for your note received this morning; and now for another "wriggle." According to my notions, the sub-arctic species would advance in a body, advancing so as to keep climate nearly the same; and as long as they did this I do not believe there would be any tendency to change, but only when the few got amongst foreign associates. When the tropical species retreated as far as they could to the equator they would halt, and then the confusion would spread back in the line of march from the far north, and the strongest would struggle forward, etc., etc. (But I am getting quite poetical in my wriggles). In short, I THINK the warm-temperates would be exposed very much longer to those causes which I believe are alone efficient in producing change than the sub-arctic; but I must think more over this, and have a good wriggle. I cannot quite agree with your proposition that because the sub-arctic have to travel twice as far they would be more liable to change. Look at the two journeys which the arctics have had from N. to S. and S. to N., with no change, as may be inferred, if my doctrine is correct, from similarity of arctic species in America and Europe and in the Alps. But I will not weary you; but I really and truly think your last objection is not so strong as it looks at first. You never make an objection without doing me much good. Hurrah! a seed has just germinated after 21 1/2 hours in owl's stomach. This, according to ornithologists' calculation, would carry it God knows how many miles; but I think an owl really might go in storm in this time 400 or 500 miles. Adios.

Owls and hawks have often been seen in mid-Atlantic.

(336/1. An interesting letter, dated November 23rd, 1856, occurs in the "Life and Letters," II., page 86, which forms part of this discussion. On page 87 the following passage occurs: "I shall have to discuss and think more about your difficulty of the temperate and sub-arctic forms in the S. hemisphere than I have yet done. But I am inclined to think that I am right (if my general principles are right), that there would be little tendency to the formation of a new species during the period of migration, whether shorter or longer, though considerable variability may have supervened.)

LETTER 337. TO J.D. HOOKER. Down, December 10th {1856}.

It is a most tiresome drawback to my satisfaction in writing that, though I leave out a good deal and try to condense, every chapter runs to such an inordinate length. My present chapter on the causes of fertility and sterility and on natural crossing has actually run out to 100 pages MS., and yet I do not think I have put in anything superfluous...

I have for the last fifteen months been tormented and haunted by land-mollusca, which occur on every oceanic island; and I thought that the double creationists or continental extensionists had here a complete victory. The few eggs which I have tried both sink and are killed. No one doubts that salt water would be eminently destructive to them; and I was really in despair, when I thought I would try them when torpid; and this day I have taken a lot out of the sea-water, after exactly seven days' immersion. (337/1. This method of dispersal is not given in the "Origin"; it seems, therefore, probable that further experiments upset the conclusion drawn in 1856. This would account for the satisfaction expressed in the following year at the discovery of another method, on which Darwin wrote to Sir J.D. Hooker: "The distribution of fresh-water molluscs has been a horrid incubus to me, but I think I know my way now. When first hatched they are very active, and I have had thirty or forty crawl on a dead duck's foot; and they cannot be jerked off, and will live fifteen or even twenty-four hours out of water" ("Life and Letters," II., page 93). The published account of these experiments is in the "Origin," Edition I., page 385.) Some sink and some swim; and in both cases I have had (as yet) one come to life again, which has quite astonished and delighted me. I feel as if a thousand-pound weight was taken off my back. Adios, my dear, kind friend.

I must tell you another of my profound experiments! {Frank} said to me: "Why should not a bird be killed (by hawk, lightning, apoplexy, hail, etc.) with seed in its crop, and it would swim?" No sooner said than done: a pigeon has floated for thirty days in salt water with seeds in its crop, and they have grown splendidly; and to my great surprise even tares (Leguminosae, so generally killed by sea-water), which the bird had naturally eaten, have grown well. You will say gulls and dog-fish, etc., would eat up the carcase, and so they would 999 times out of a thousand, but one might escape: I have seen dead land-birds in sea-drift.

LETTER 338. ASA GRAY TO CHARLES DARWIN.

(338/1. In reply to Darwin's letter given in "Life and Letters," II., page 88.)

Cambridge, Mass., February 16th, 1857.

I meant to have replied to your interesting letter of January 1st long before this time, and also that of November 24th, which I doubt if I have ever acknowledged. But after getting my school-book, Lessons in Botany, off my hands — it taking up time far beyond what its size would seem to warrant — I had to fall hard at work upon a collection of small size from Japan — mostly N. Japan, which I am only just done with. As I expected, the number of species common to N. America is considerably increased in this collection, as also the number of closely representative species in the two, and a pretty considerable number of European species too. I have packed off my MSS. (though I hardly know what will become of it), or I would refer you to some illustrations. The greater part of the identical species (of Japan and N. America) are of those extending to or belonging to N.W. coast of America, but there are several peculiar to Japan and E. U. States: e.g. our Viburnum lantanoides is one of Thunberg's species. De Candolle's remarkable case of Phryma, which he so dwells upon, turns out, as Dr. Hooker said it would, to be only one out of a great many cases of the same sort. (Hooker brought Monotropa uniflora, you know, from the Himalayas; and now, by the way, I have it from almost as far south, i.e., from St. Fee, New Granada)...

Well, I never meant to draw any conclusions at all, and am very sorry that the only one I was beguiled into should "rile" (338/2. "One of your conclusions makes me groan, viz., that the line of connection of the strictly alpine plants is through Greenland. I should extremely like to see your reasons published in detail, for it 'riles' me (this is a proper expression, is it not?) dreadfully" (Darwin to Gray, January 1st, 1857, "Life and Letters," II., page 89).) you, as you say it does, — that on page 73 of my second article: for if it troubles you it is not likely to be sound. Of course I had no idea of laying any great stress upon the fact (at first view so unexpected to me) that one-third of our alpine species common to Europe do not reach the Arctic circle; but the remark which I put down was an off-hand inference from what you geologists seem to have settled — viz., that the northern regions must have been a deal cooler than they are now — the northern limit of vegetation therefore much lower than now — about the epoch when it would seem probable that the existing species of our plants were created. At any rate, during the Glacial period there could have been no phaenogamous plants on our continent anywhere near the polar regions; and it seems a good rule to look in the first place for the cause or reason of what now is, in that which immediately preceded. I don't see that Greenland could help us much, but if there was any interchange of species between N. America and N. Europe in those times, was not the communication more likely to be in lower latitudes than over the pole?

If, however, you say — as you may have very good reasons for saying — that the existing species got their present diffusion before the Glacial epoch, I should have no answer. I suppose you must needs assume very great antiquity for species of plants in order to account for their present dispersion, so long as we cling — as one cannot but do — to the idea of the single birthplace of species.

I am curious to see whether, as you suggest, there would be found a harmony or close similarity between the geographical range in this country of the species common to Europe and those strictly representative or strictly congeneric with European species. If I get a little time I will look up the facts: though, as Dr. Hooker rightly tells me, I have no business to be running after side game of any sort, while there is so much I have to do — much more than I shall ever do probably — to finish undertakings I have long ago begun.

...As to your P.S. If you have time to send me a longer list of your protean genera, I will say if they seem to be protean here. Of those you mention: —

Salix, I really know nothing about.

Rubus, the N. American species, with one exception, are very clearly marked indeed.

Mentha, we have only one wild species; that has two pretty well-marked forms, which have been taken for species; one smooth, the other hairy.

Saxifraga, gives no trouble here.

Myosotis, only one or two species here, and those very well marked.

Hieracium, few species, but pretty well marked.

Rosa, putting down a set of nominal species, leaves us four; two of them polymorphous, but easy to distinguish...

LETTER 339. TO J.D. HOOKER. Down, {1857?}

One must judge by one's own light, however imperfect, and as I have found no other book (339/1. A. De Candolle's "Geographie Botanique," 1855.) so useful to me, I am bound to feel grateful: no doubt it is in main part owing to the concentrated light of the noble art of compilation. (339/2. See Letter 49.) I was aware that he was not the first who had insisted on range of Monocots. (Was not R. Brown {with} Flinders?) (339/3. M. Flinders' "Voyage to Terra Australis in 1801-3, in H.M.S. 'Investigator'"; with "Botanical Appendix," by Robert Brown, London, 1814.), and I fancy I only used expression "strongly insisted on," — but it is quite unimportant.

If you and I had time to waste, I should like to go over his {De Candolle's} book and point out the several subjects in which I fancy he is original. His remarks on the relations of naturalised plants will be very useful to me; on the ranges of large families seemed to me good, though I believe he has made a great blunder in taking families instead of smaller groups, as I have been delighted to find in A. Gray's last paper. But it is no use going on.

I do so wish I could understand clearly why you do not at all believe in accidental means of dispersion of plants. The strongest argument which I can remember at this instant is A. de C., that very widely ranging plants are found as commonly on islands as over continents. It is really provoking to me that the immense contrast in proportion of plants in New Zealand and Australia seems to me a strong argument for non-continuous land; and this does not seem to weigh in the least with you. I wish I could put myself in your frame of mind. In Madeira I find in Wollaston's books a parallel case with your New Zealand case — viz., the striking absence of whole genera and orders now common in Europe, and (as I have just been hunting out) common in Europe in Miocene periods. Of course I can offer no explanation why this or that group is absent; but if the means of introduction have been accidental, then one might expect odd proportions and absences. When we meet, do try and make me see more clearly than I do, your reasons.

LETTER 340. TO J.D. HOOKER. Down, November 14th {1858}.

I am heartily glad to hear that my Lyellian notes have been of the slightest use to you. (340/1. The Copley Medal was given to Sir Charles Lyell in 1858. Mr. Darwin supplied Sir J.D. Hooker, who was on the Council of the Royal Society, with notes for the reasons for the award. See Letter 69.) I do not think the view is exaggerated...

Your letter and lists have MOST DEEPLY interested me. First for less important point, about hermaphrodite trees. (340/2. See "Life and Letters," II., page 89. In the "Origin," Edition I., page 100, the author quotes Dr. Hooker to the effect that "the rule does not hold in Australia," i.e., that trees are not more generally unisexual than other plants. In the 6th edition, page 79, Darwin adds, "but if most of the Australian trees are dichogamous, the same result would follow as if they bore flowers with separated sexes.") It is enough to knock me down, yet I can hardly think that British N. America and New Zealand should all have been theoretically right by chance. Have you at Kew any Eucalyptus or Australian Mimosa which sets its seeds? if so, would it be very troublesome to observe when pollen is mature, and whether pollen-tubes enter stigma readily immediately that pollen is mature or some little time afterwards? though if pollen is not mature for some little time after flower opens, the stigma might be ready first, though according to C.C. Sprengel this is a rarer case. I wrote to Muller for chance of his being able and willing to observe this.

Your fact of greater number of European plants (N.B. — But do you mean greater percentage?) in Australia than in S. America is astounding and very unpleasant to me; for from N.W. America (where nearly the same flora exists as in Canada?) to T. del Fuego, there is far more continuous high land than from Europe to Tasmania. There must have, I should think, existed some curious barrier on American High-Road: dryness of Peru, excessive damp of Panama, or some other confounded cause, which either prevented immigration or has since destroyed them. You say I may ask questions, and so I have on enclosed paper; but it will of course be a very different thing whether you will think them worth labour of answering.