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, Ithought I would calculate the proportions of, for instance, the INTRODUCEDCompositae in Great Britain to all the introduced plants, and the result was, 10/92 = 1/9.2. In our ABORIGINAL or indigenous flora the proportion is 1/10; and in many other cases I found an equally striking correspondence. I then took your Manual, and worked out the same question;here I find in the Compositae an almost equally striking correspondence, viz. 24/206 = 1/8 in the introduced plants, and 223/1798 = 1/8 in the indigenous; but when I came to the other families I found the proportion entirely different, showing that the coincidences in the British Flora were probably accidental!
You will, I presume, give the proportion of the species to the genera, i.e., show on an average how many species each genus contains; though Ihave done this for myself.
If it would not be too troublesome, do you not think it would be very interesting, and give a very good idea of your Flora, to divide the species into three groups, viz., (a) species common to the old world, stating numbers common to Europe and Asia; (b) indigenous species, but belonging to genera found in the old world; and (c) species belonging to genera confined to America or the New World. To make (according to my ideas) perfection perfect, one ought to be told whether there are other cases, like Erica, of genera common in Europe or in Old World not found in your area. But honestly I feel that it is quite ridiculous my writing to you at such length on the subject; but, as you have asked me, I do it gratefully, and write to you as I should to Hooker, who often laughs at me unmercifully, and I am sure you have better reason to do so.
There is one point on which I am MOST anxious for information, and Imention it with the greatest hesitation, and only in the FULL BELIEF that you will believe me that I have not the folly and presumption to hope for a second that you will give it, without you can with very little trouble.
The point can at present interest no one but myself, which makes the case wholly different from geographical distribution. The only way in which, Ithink, you possibly could do it with little trouble would be to bear in mind, whilst correcting your proof-sheets of the Manual, my question and put a cross or mark to the species, and whenever sending a parcel to Hooker to let me have such old sheets. But this would give you the trouble of remembering my question, and I can hardly hope or expect that you will do it. But I will just mention what I want; it is to have marked the "close species" in a Flora, so as to compare in DIFFERENT Floras whether the same genera have "close species," and for other purposes too vague to enumerate.
I have attempted, by Hooker's help, to ascertain in a similar way whether the different species of the same genera in distant quarters of the globe are variable or present varieties. The definition I should give of a "CLOSE SPECIES" was one that YOU thought specifically distinct, but which you could conceive some other GOOD botanist might think only a race or variety; or, again, a species that you had trouble, though having opportunities of knowing it well, in discriminating from some other species. Supposing that you were inclined to be so very kind as to do this, and could (which I do not expect) spare the time, as I have said, a mere cross to each such species in any useless proof-sheets would give me the information desired, which, I may add, I know must be vague.
How can I apologise enough for all my presumption and the extreme length of this letter? The great good nature of your letter to me has been partly the cause, so that, as is too often the case in this world, you are punished for your good deeds. With hearty thanks, believe me, Yours very truly and gratefully, CH. DARWIN.
CHARLES DARWIN TO J.D. HOOKER.
Down, 18th [July, 1855].
...I think I am getting a MILD case about Charlock seed (In the "Gardeners' Chronicle", 1855, page 758, appeared a notice (half a column in length) by my father on the "Vitality of Seeds." The facts related refer to the "Sand-walk"; the wood was planted in 1846 on a piece of pasture land laid down as grass in 1840. In 1855, on the soil being dug in several places, Charlock (Brassica sinapistrum) sprang up freely. The subject continued to interest him, and I find a note dated July 2nd, 1874, in which my father recorded that forty-six plants of Charlock sprang up in that year over a space (14 x 7 feet) which had been dug to a considerable depth.); but just as about salting, ill-luck to it, I cannot remember how many years you would allow that Charlock seed might live in the ground. Next time you write, show a bold face, and say in how many years, you think, Charlock seed would probably all be dead. A man told me the other day of, as Ithought, a splendid instance,-- and SPLENDID it was, for according to his evidence the seed came up alive out of the LOWER PART of the LONDON CLAY!!
I disgusted him by telling him that Palms ought to have come up.
You ask how far I go in attributing organisms to a common descent; I answer I know not; the way in which I intend treating the subject, is to show (ASFAR AS I CAN) the facts and arguments for and against the common descent of the species of the same genus; and then show how far the same arguments tell for or against forms, more and more widely different: and when we come to forms of different orders and classes, there remain only some such arguments as those which can perhaps be deduced from similar rudimentary structures, and very soon not an argument is left.
[The following extract from a letter to Mr. Fox [October, 1855 (In this year he published ('Phil. Mag.' x.) a paper 'On the power of icebergs to make rectilinear uniformly-directed grooves across a submarine undulatory surface.'") gives a brief mention of the last meeting of the British Association which he attended:] "I really have no news: the only thing we have done for a long time, was to go to Glasgow; but the fatigue was to me more than it was worth, and E. caught a bad cold. On our return we stayed a single day at Shrewsbury, and enjoyed seeing the old place. I saw a little of Sir Philip (Sir P. Egerton was a neighbour of Mr. Fox.) (whom Iliked much), and he asked me "why on earth I instigated you to rob his poultry-yard?' The meeting was a good one, and the Duke of Argyll spoke excellently."]