I have just read your article. As far as my judgment goes it is excellent and could not be improved. You have skimmed the cream off the whole subject. It is also very clear. One or two sentences near the beginning seem rather too strong, as I have marked with pencil, without attending to style. I have made one or two small suggestions. If you can find my account in 'Nature' (last summer I think)[30] about the hybrid Chinese geese [being fertile] _inter se_, it would be worth adding, and would require only two or three lines. I do not suppose you wish to add, but in my paper on Lythrum, and I think requoted in 'Var. under Dom.' vol. ii. 2nd edit. bottom of page 167, I have a good sentence about a man finding two vars. of Lythrum, and testing them by fertility, and coming to egregiously wrong conclusion. I think your idea of reference to best books and short history of subject good. By the way, you have made me quite proud of my chapter on Hybridism, I had utterly forgotten how good it appears when dressed up in your article. Yours very sincerely, CHARLES DARWIN. I have had a hunt and found my little article on Geese, which please hereafter return. _From G. J. Romanes to C. Darwin, Esq._ 18 Cornwall Terrace, Regent's Park, N.W.: December 10, 1880. I return by this post the book on Hybridism, with many thanks. It has been of great use to me in giving an abstract of the history. I have read your own book with an amount of pleasure that I cannot express. One idea occurred to me with reference to luminous stimulation, which, if it has not already occurred to you, would be well worth trying. The suggestion suggests itself. How about the period of latent stimulation in these non-nervous and yet irritable tissues? And especially with reference to luminous stimulation it would be most interesting to ascertain whether the tissues are affected by brief _flashes_ of light. If you had an apparatus to give bright electrical sparks in a dark room, and were to expose one of your plants to flashes of timed intervals between each other, you might ascertain, first, whether _any_ number of sparks in _any_ length of time would affect the plants at all; and second, if so, what number in a given time. I should not wonder (from some of my experiments on Medusæ, see 'Phil. Trans.' vol. clxvii. pt. ii. pp. 683-4) if it would turn out that a continuous uninterrupted series of sparks, however bright, would produce no effect at all, owing to the plant tissues being too sluggish to admit of being affected by a succession of stimuli each of such brief duration. But if any effect were produced, it would still be interesting to make out whether this interrupted source of flashing light were considerably less effective than a continuous source of the same intensity. Very sincerely and most respectfully yours, GEO. J. ROMANES.