My dear F.

I have very little to tell you scientifically & nothing about anything else.— I have got a Philodendron & a Dendrobium from Kew with fine aerial roots & which have turned for the light; but they will not now move; & they do so I suppose only when growing rapidly.—²

I have settled well that the stems of 2 spc. of Ipomœa are not in the least Heliotropic, for I have carefully compared 22 semicircles moving to the light with 22 semicircles moving from the light, & on an average they agreed within 3 minutes.³

The only other thing which I have done is proving that the tip of radicle of Gossypium herbaceum is very sensitive to touch of caustic & bends from the touched side. This is good for bits of card did not act at all well. Also the tip when blackened for $\frac{1}{2}$mm stops the geotropism of horizontally extended roots completely.⁴

At some time or another I shall be anxious for you to touch a cell with your point & see if it influences at all the current of protoplasm: I saw lately a notice by Wright (I think in Mic. Journal) that passing without any injury cells of some Algae caused all the protoplasm to collect up at the further end.⁵

On Thursday we go to London to receive medal & Laura Forster has lent us her house most kindly; & your mother & I go on Saturday there & stay till Tuesday Morning. Laura & Henrietta will stay here to take care of Ubba & the 2 little boys.—⁶ Your mother declares that I want & shall have rest; but it will be very tedious with nothing on earth to do.— I have just asked whether Ubba had any message to you & he gave a most emphatic nod, but I could extract only “I don’t know”. His expression really gets more charming every day.

Your affect Father | C. Darwin