My dear Frank

Here we are & remain till Tuesday morning, & George comes down to night.—² I had a very busy day yesterday; first good talk with B. Sanderson who was interested about the circumnutation & starting movement under microscope of Dionæa & means to go into it in relation to electric currents:³ then a very pleasant luncheon at Pagets, & in evening a talk with Lauder Brunton, who is reading Zoonomia & is enthusiastic about D^r. D.—⁴

Your letter arrived just as we were starting for Q. Anne St: I am very sorry that Sachs is so sceptical, for I w^d. rather convert him than any other half-dozen-Botanists put together; but I expected it.⁵ No doubt something may be said against caustic. I do not understand why when radicles are pointed perpendicularly down & then tips are cauterised they grow out wildly on all sides, & this does not happen when they are extended horizontally; I suspect that ‘Sachs’ curvature’ comes into action only with perpendicular roots, & will set to work & observe this point.⁶ It seems to me a sufficient explanation of geotropism acting after 24 h, though not at first, that some of the cells of the apex regenerate themselves.— I sh^d. not at all believe in the sense of geotropism residing in apex, if I did not feel sure about the sense of contact residing there. It was observing radicles of Beans sliding down unsmoked glass, & the manner in which they turned at right angles (quite unlike any mechanical bending) when their tips encountered a strip of wood or glass cemented across the plate, that made me first suspect sensitiveness & try the little square of card first with gum & then shell lac. It is the side of conical tip which is alone sensitive.— Whenever card got parallel to radicle it did not act.—

In crawling down glass-plate side of conical apex does not touch glass-surface, except just at first, when it first comes into contact & then it rises a trifle & adjusts itself. I wish it were possible to try radicles of mustard with black cap instead of caustic—⁷ Though it is quite possible their sensitiveness may not be confined to tip— nor sh^d I expect it, to be so confined except in cases, as of aerial roots, when it is probably of service to plant.— Great man as Sachs is, I am not even staggered by him.

I am tired— goodbye my dear old fellow | C. Darwin