I return by this post the book on Hybridism, with many thanks.¹ 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.²

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)³ 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.