CHARLES DARWIN TO ASA GRAY. Down, June 8th [1855].
My dear Sir,
I thank you cordially for your remarkably kind letter of the 22d. ult., and for the extremely pleasant and obliging manner in which you have taken my rather troublesome questions. I can hardly tell you how much your list of Alpine plants has interested me, and I can now in some degree picture to myself the plants of your Alpine summits. The new edition of your Manual is CAPITAL news for me. I know from your preface how pressed you are for room, but it would take no space to append (Eu) in brackets to any European plant, and, as far as I am concerned, this would answer every purpose. (This suggestion Dr. Gray adopted in subsequent editions.) From my own experience, whilst making out English plants in our manuals, it has often struck me how much interest it would give if some notion of their range had been given; and so, I cannot doubt, your American inquirers and beginners would much like to know which of their plants were indigenous and which European. Would it not be well in the Alpine plants to append the very same addition which you have now sent me in MS.? though here, owing to your kindness, I do not speak selfishly, but merely pro bono Americano publico. I presume it would be too troublesome to give in your manual the habitats of those plants found west of the Rocky Mountains, and likewise those found in Eastern Asia, taking the Yenesei (?),--which, if I remember right, according to Gmelin, is the main partition line of Siberia. Perhaps Siberia more concerns the northern Flora of North America. The ranges of plants to the east and west, viz., whether most found are in Greenland and Western Europe, or in E. Asia, appears to me a very interesting point as tending to show whether the migration has been eastward or westward. Pray believe me that I am most entirely conscious that the ONLY USE of these remarks is to show a botanist what points a non-botanist is curious to learn; for I think every one who studies profoundly a subject often becomes unaware [on] what points the ignorant require information. I am so very glad that you think of drawing up some notice on your geographical distribution, for the air of the Manual strikes me as in some points better adapted for comparison with Europe than that of the whole of North America. You ask me to state definitely some of the points on which I much wish for information; but I really hardly can, for they are so vague; and I rather wish to see what results will come out from comparisons, than have as yet defined objects. I presume that, like other botanists, you would give, for your area, the proportion (leaving out introduced plants) to the whole of the great leading families: this is one point I had intended (and, indeed, have done roughly) to tabulate from your book, but of course I could have done it only VERY IMPERFECTLY. I should also, of course, have ascertained the proportion, to the whole Flora, of the European plants (leaving out introduced) AND OF THE SEPARATE GREAT FAMILIES, in order to speculate on means of transportal. By the way, I ventured to send a few days ago a copy of the "Gardeners' Chronicle" with a short report by me of some trifling experiments which I have been trying on the power of seeds to withstand sea water. I do not know whether it has struck you, but it has me, that it would be advisable for botanists to give in WHOLE NUMBERS, as well as in the lowest fraction, the proportional numbers of the families, thus I make out from your Manual that of the INDIGENOUS plants the proportion of the Umbelliferae are 36/1798 = 1/49; for, without one knows the WHOLE numbers, one cannot judge how really close the numbers of the plants of the same family are in two distant countries; but very likely you may think this superfluous. Mentioning these proportional numbers, I may give you an instance of the sort of points, and how vague and futile they often are, which I ATTEMPT to work out...; reflecting on R. Brown's and Hooker's remark, that near identity of proportional numbers of the great families in two countries, shows probably that they were once continuously united, I thought I would calculate the proportions of, for instance, the INTRODUCED Compositae in Great Britain to all the introduced plants, and the result was, 10/92 = 1/9.2.