–besides 20 or 30 of Introd. matter² —(all simple & for students’ use)—among which is 4 pages of statistics.—of which I enclose you a proof of the last page, that you may see what our flora amounts to.³ The genera of the Crypt. Ferns—down to Hepaticæ—are illustrated in 14 crowded plates—so that the volume has become rather formidable as a Class-book—which is what it is intended for—

I have revised the last proofs to-day— The publishers will bring it out some time in August.— Meanwhile, I am going to have a little holiday, which I have earned, little as I can spare the time for it—and my wife and I start on Friday to visit my Mother and friends in W. New York, and on our way back I will look in upon the scientific meeting at Albany on the 20^th inst. or later—just to meet some old friends there.⁴

Why could not you come over, on the urgent invitation given to European savans—& free passage provided back & forth in the steamers! Yet I believe nobody is coming. Will you not come next year, if a special invitation is sent you on the same terms?

Boott⁵ lately sent me your photograph,⁶ which (tho. not a very perfect one) I am well pleased to have.—

But there is another question in your last letter—one about which a person can only give an impression— And my impression is that—speaking of plants of a well-known flora—that what we call intermediate varieties are generally less numerous in individuals than the two states which they connect. That this would be the case in a Flora where things are put as they naturally should be, I do not much doubt, and the wider are your views about species (say for instance with D^r. Hooker’s very latitudinarian notions) the more plainly would this appear.—

But practically two things stand hugely in the way of any application of the fact or principle, if such it be, 1, Our choice of what to take as the typical forms very often is not free. We take, e.g. for one of them the particular form of which Linnæus, say, happened to have a specimen sent him, and on which established the species; and I know more than one case in which that is a rare form of a common species: the other var. will perhaps be the opposite extreme—whether the most common or not, or will be what L. or [Willd],⁷ say, described as a 2^d species.— Here various intermediate forms may be the most abundant; 2^d It is just the same thing now, in respect to specimens coming in from our new western country. The form which first comes & is described & named, determines the spec. char.— And this long sticks as the type, tho, in fact it may be far from the most common form.

Yet of plants very well known in all their aspects, I can think of several of which we recognize 2 leading forms, and rarely see anything really intermediate,—such as our Mentha borealis, its hairy and its smooth varieties.

Your former query, about the variability of Naturalized plants as compared with others of same genera, I had not forgotten, but have taken no steps to answer.— I was going hereafter to take up our list of naturalized plants & consider them, it did not fall into my plan to do it yet. Off hand I can only say that it does not strike me that our introduced plants generally are more variable, nor as variable, perhaps, as the indigenous. But this is a mere guess,—

When you get my sheets of 1^st part of article in Sill. Journal,⁸ remember that I shall be most glad of free critical comments; and the earlier I get them, the greater use they will be to me.

D^r. Hooker writes me that he is to be off on the 12^th inst to Switzerland, &c.— So I cannot write to him till his return.

One more favor: Do not I pray you speak of your letters troubling me. I should be sorry indeed to have you stop, or write more rarely, even tho’ mortified to find that I can so seldom give you the information you might reasonably expect from

Yours most | sincerely | Asa Gray