From Charles James Fox Bunbury 7 February 1856
February 7. 1856
My dear Darwin,
As I know you are much interested in the questions relating to varieties & species among plants as well as 〈an〉imals, I will mention to you a 〈c〉ase which has excited my curiosity a good deal. In the Journal of the Horticultural Society, a few years ago, (5th vol. p. 31 & 32,) Lindley described & figured what he believed to be a very extraordinary variety of Colletia spinosa (a South American shrub),1 said to have been raised from seed of that species in Lady Rolle’s garden in Devonshire.2 The deviation from the original type, as shortly as I can state it, is mainly this: that 〈 〉 spines, or spiny-pointed branches 〈in〉stead of being nearly cylindrical, are so excessively dilated vertically, as to form nearly right-angled triangles, with 〈 〉 base (along the branch) often equal to the perpendicular. And this is a real extension of the wood, not merely of the cellular substance.3 Now 〈the〉 curious thing is, that this same variety (if such it be) grows wild in South America. Lindley’s description & figure agree perfectly (tho’ he seems to have quite overlooked this,) with those which Sir W. Hooker gives, in the first volume of the Botanical Miscellany, of his Colletia cruciata,4 found by Dr Gillies on sand hills near Maldonado.5 I find in Mr Fox’s collection, several fine dried specimens of the same, gathered also at Maldonado.6
I wonder whether you met with it there? If the origin of this plant in cultivation from seeds of Colletia spinosa be really certain, it is a very curious case of a seminal variety having 〈 〉 the appearance of a distinct species, & occurring in the wild state as well as in cultivation but I confess the evidence as to its origin does not appear to me quite satisfactory.7 You probably have the means of referring to the Journal of the Hort. Soc.,—I wish you would tell me what you think.
I was told last summer that you were becoming a believer in the unlimited mutability of species,—almost to the extent of the “Vestiges of Creation.”8 I suspect this is not strictly correct. I should be very glad to hear any thing you may think fit to tell me about your researches into the laws of species, a subject on which I hope you will one day enlighten us very much; also I should like to know whether you have obtained any further results as to the germination of seeds ex〈pos〉ed to salt water.9 I am afraid I have not yet any remarkable facts to send you in reference to Cape plants. 10 I forget whether I mentioned Frankenia to you as one of those genera which have their headquarters in Europe, but which have some truly indigenous species at the Cape of Good Hope. One species indeed, Frankenia lævis, appears to be common to Europe & the Cape; whether it is found in any intermediate country I do not know; but there are one or two peculiar to the Cape, with a very strong likeness certainly to those of the northern hemisphere, but distinct, as specific distinctness is generally understood. Dianthus I think I mentioned to you before: it is an interesting case, because I believe the genus exists nowhere in the southern hemisphere except at the Cape, & the genus is a peculiarly natural & well-marked one. 11 We have a vast deal yet to learn with respect to the limits of species; the excessive differences in the views of different 〈na〉turalists on this point intro〈duces〉 c〈onf〉usion & uncertainty into 〈 〉 reasonings on the geogra〈phy of〉 plants & animals. When 〈 〉 that what according to Duval’s views are nearly 50 different species of Solanum,12 are considered by Bentham as all referable to the one Solanum nigrum; & that another botanist has made 12 species out of our common White Water-lily; it is rather bewildering. I am myself quite ready to believe that the range of variation of species may be greater than even the most cautious botanists at present allow for; but I should be slow to believe that it is unlimited.
Ever yours very sincerely | C J F Bunbury
Has heard CD is much interested in questions relating to varieties and species. Mentions a case of a seminal variety of Colletia spinosa, described by John Lindley, which appears identical with another wild species of Colletia from S. America. Hopes CD will one day "enlighten us very much" on "the laws of species". There are many different views on the limits of species; M. F. Dunal made 50 species of Solanum which George Bentham considers are all varieties of S. nigrum.