I am particularly obliged for your facts about solitary islands having several species of peculiar genera; it knocks on the head some analogies of mine; the point stupidly never occurred to me to ask about. I am amused at your anathemas against variation and co.; whatever you may be pleased to say, you will never be content with simple species, "as they are." I defy you to steel your mind to technicalities, like so many of our brother naturalists. I am much pleased that I thought of sending you Forbes' article. (19/2. E. Forbes' celebrated paper "Memoirs of the Geological Survey of Great Britain," Volume I., page 336, 1846. In Lyell's "Principles," 7th Edition, 1847, page 676, he makes a temperate claim of priority, as he had already done in a private letter of October 14th, 1846, to Forbes ("Life of Sir Charles Lyell," 1881, Volume II., page 106) both as regards the Sicilian flora and the barrier effect of mountain-chains. See Letter 20 for a note on Forbes.) I confess I cannot make out the evidence of his time-notions in distribution, and I cannot help suspecting that they are rather vague. Lyell preceded Forbes in one class of speculation of this kind: for instance, in his explaining the identity of the Sicily Flora with that of South Italy, by its having been wholly upraised within the recent period; and, so I believe, with mountain-chains separating floras. I do not remember Humboldt's fact about the heath regions. Very curious the case of the broom; I can tell you something analogous on a small scale. My father, when he built his house, sowed many broom-seeds on a wild bank, which did not come up, owing, as it was thought, to much earth having been thrown over them. About thirty-five years afterwards, in cutting a terrace, all this earth was thrown up, and now the bank is one mass of broom. I see we were in some degree talking to cross-purposes; when I said I did [not] much believe in hybridising to any extent, I did not mean at all to exclude crossing. It has long been a hobby of mine to see in how many flowers such crossing is probable; it was, I believe, Knight's view, originally, that every plant must be occasionally crossed. (19/3. See an article on "The Knight-Darwin law" by Francis Darwin in "Nature," October 27th, 1898, page 630.) I find, however, plenty of difficulty in showing even a vague probability of this; especially in the Leguminosae, though their [structure?] is inimitably adapted to favour crossing, I have never yet met with but one instance of a NATURAL MONGREL (nor mule?) in this family.