being able to assign a vera causa. Heer has the disadvantage of having no known cause to assign; but he shows that things do not appear to have proceeded as Darwin’s theory requires. It does seem as if there were times of peculiar change as well as of great stability. But were this time of change and that of stability simultaneous for the species of a flora? And does Heer allow enough for the species which now occur under many forms,--show great polymorphism. I continually meet with these in the North American flora; in which the dying out of some forms, and their replacing by others, which may well take place in time, would, in effect, just give a change like that to be accounted for. But I cannot say that these varieties come in insensibly, very likely not. Now, to speak of myself. My summer was much frittered away; the superintending of the new building for my herbarium just preventing any serious study. The autumn was devoted to the removal and rearrangement of plants and books, and to assisting Charles Wright in the collation and distribution into sets of his collections in Cuba for the last three years past; very full and interesting collections, and requiring much care and labor, on account of this distribution being a continuation of former distributions. I laid out into the sets every specimen with my own hands, Mr. Wright adding the tickets and numbers. It was an immense labor, and was finished only at the close of the last day of the year.... I mean to prepare for “Silliman’s Journal” a brief and simple notice of the edifice for my herbarium, so I will not speak further of it here; further than to say that I am well satisfied, only I sadly need a curator! And now, I turn to your letter of September 29, and ask your pardon for having so long neglected it. Your letters, your reflections upon social and political, as well as upon scientific questions, are always very interesting and instructive to me. I regret that I can render so little return in kind.... As to our national troubles, the prospect brightens that we shall end the rebellion and slavery before long. God grant it. Believe me to be, as ever, my dear De Candolle, very faithfully yours, A. GRAY. TO GEORGE ENGELMANN. February 14, 1865. ... Wright is here, distributing and finishing up his North Pacific Expedition Collection; ... will return to Cuba in a month or two, to take a year or two more there, revisit some old parts and explore some new; then I urge Hayti, but Wright seems rather loth. Rothrock--from northwestern Pennsylvania--is a bright lively pupil of mine for last three or four years, when not serving his country in the army, where he has done good service as private in infantry, and as captain in Pennsylvania cavalry, etc. He had to leave his thesis partly unfinished. But the real credit of all belongs to him. His father is M. D., and he is now studying medicine, attending lectures at Philadelphia. But botany is in him, and will probably come out....