Dear Darwin

Thanks for the books. You have set me thinking much on varieties in great versus small genera. I am obstinately inclined to take general monographs for data in preference to local Floras, for the general works alone seem to me to give a fair chance of the species being uniformly treated—because Local Floras consist of diag 1 Local plants,—these we agree are not so variable as mundane plants. 2. Mundane plants—of which only one form is found in the said local area, &

which are hence not treated as variable in the Flora of that area. 3 Mundane plants of which two or more varieties are found in the area.ramme

Now as you increase your area the small local (ie. invariable) genera do not reappear—but the small mundane genera do with an increased number of var^s. & the large mundane genera with their variable species also relatively increase.

Is this not so— be that as it may I have just got Weddells monograph of Urticæ¹ from binder back & as I told you that I thought it would prove as unexceptionable food for analysis as may be—I have roughly tabulated the results & enclose them²

Weddell has reduced both the large & small genera enormously & consistently, & I attach the greater confidence to his work from the close accordance between the relative number of sp. to var^s. in large & small genera.

Again if the species of small local genera are themselves local it follows that we procure fewer specimens of the species of such genera than of large & hence make fewer varieties. This any general Herbarium shows. A genus of one species presents only a single specimen much oftener than a genus of 10 species does only 10 specimens.

Again suppose I am naming by comparison or otherwise a species of a large genus, I find it agrees a little with many species, exactly with none, but most nearly one— I hesitate & am in difficulty & my tendency is to make it a var. of that it is nearest all the more if the latter is itself variable.— but in naming in the same way a species of a small genus I find no such difficulty it is perhaps not exactly like the species to which I refer it, still it is not the least like anything else. Now I made a var of my first plant partly lest my successor should refer it to any of the other species which it resembled. from missing it under the vars of that I refer it to. but in the second case no such precaution is necessary

Ever dear Darwin yrs | Jos D Hooker