Mulder is very ingenious; but we can blow up the whole line of his arguments, and show that it all amounts to nothing; that he has not in this advanced our knowledge a particle; and that his generalizations are unsound. Why did you not have a part of my article reprinted in New York? That would be the best reply to all his stuff. The printing of my book will be through next week. March 30. I am now half through, and have got almost done with Fungi. The audience take so much to the “Cryptogamic matters,” especially the afternoon audience, which is as a whole the most intelligent and refined, that I let them run on, and they will occupy the whole course, except three lectures. I gave one lecture, generally thought nearly the best, on the large Fungi, mushrooms, truffles, morels, puff-balls, with some good general matters. To-day I have taken the small ones, moulds, mildews, rust, and smut in wheat, with superb illustrations. Ergot is still left over, along with the diseases in potatoes, the plant of fermentation, the Botrytis that kills silk-worms, with some recapitulatory matters on spontaneous generation, which must be cooked up for Friday. Then comes Algæ; the large proper ones (Lecture 8), of which a fine series of illustrations is now nearly done. Lecture 9. Then the low, minute forms and Confervæ come, and gory dew, red snow, superbly illustrated, ending with diatoms, transitions to corallines through sponge, etc., and the locomotive spores of Confervæ, Zoösporæ. Lecture 10. Whole subject of spontaneous movements and sensibility in flowering plants, the life of plants, etc. (treated in a somewhat original way), and the real differences between plants and animals. Lecture 11. The principles of classification. Individuals, species, their permanence, genera, orders, etc. Lecture 12. Historical development. The Linnæan system, the natural. This ends so as to give me a fine place to begin at next year.... I shall soon be able to spare Sprague to draw the Illicium, if it still holds on. But I cannot spare him just yet. He has still to copy the red-snow bank from Ross, eighteen feet long!--finish two pieces of algæ, etc., etc. TO A. DE CANDOLLE. April 5, 1845.