Since your letter came I have looked up and read the article in the “Edinburgh,” and like it much. Your few words about Genera, page 517, appear to comprise the gist of the whole matter. As to your fuller exposition, not being able to lay hands on the “Literary Gazette,” I wait to see your article in the “Journal of the Linnæan Society.” I am particularly interested in what you write of your popular “British Flora,” and the English names; and I am going to ask you to explain to me more fully the principles on which you proceed. For, if practicable, I am going to have occasion to do something of the sort here. Pray illustrate your plan a little; as I see much difficulty in carrying it out, except in so small a flora as the British, where every plant has a popular name. One additional difficulty here is that our common English names are mostly misapplied ones, and the plants that have indigenous trivial names have too many of them, varying in different parts of the country. How do you name the orders? What relation will you have between your specific names and your generic, and how many words will you allow each to consist of? Give me your names through some family, say Ranunculaceæ. If I can see my way clear, I shall follow your lead, or cause it to be followed on an occasion which will soon be presented. I wish I had known of Clitoria Mariana-acuminata, etc., in time to add it to my list in the last number of “Silliman’s Journal;” a copy of the article was sent to Dr. Hooker by post last week. I will send more, from my extras, presently. I am quite prepared for what you say about interchange of species of United States and Europe taking place via Asia, instead of across the Atlantic; but you will see there are a few, besides aquatics (Subularia, Eriocaulon, etc.), which would seem to have taken the shorter cut. As respects identical species, interchange is the only thing that, on our views of what a species is, will explain the occurrence of the same species here and there. But as to genera, I do not yet feel free to assume an interchange, or a former continuity of land, between two widely separated regions on account of their having identical genera or closely related species. I see no reason why cognate species may not have been originally given to most widely separated stations; and, as to the facts of association, can we say more than this, that the species of a genus are apt to be confined to one part of the world? Are there not too many cases to the contrary to warrant our suspecting former continuity of two remote districts on account of common genera? Peculiar genera, such as Torreya, Illicium, Philadelphus, Astilbe, etc., divided between Japan and the United States of America, indicate some peculiar relation, and are most noteworthy, but I do not see why it points to connection.