namely, to feel still more sure than I am, that a
drop of plain water never produces any effect, that I have resolved
to publish nothing this year. For I found in the record of my daily
experiments one suspicious case. I must wait till next summer. It will
be difficult to try any solid substances containing nitrogen, such
as ivory; for two quite distinct causes excite the movement, namely,
mechanical irritation and presence of nitrogen. When a solid substance
is placed on leaf it becomes clasped, but is released sooner than when a
nitrogenous solid is clasped; yet it is difficult (except with raw meat
and flies) to be sure of the result, owing to differences in vigour of
different plants. The last experiments which I tried before my
plants became too languid are very curious, and were tried by putting
microscopical atoms on the gland itself of single hairs; and it is
perfectly evident that an atom of human hair, 1/76000 of a grain (as
ascertained by weighing a length of hair) in weight, causes conspicuous
movement. I do not believe (for atoms of cotton thread acted) it is the
chemical nature; and some reasons make me doubt whether it is
actual weight; it is not the shadow; and I am at present, after many
experiments, confounded to know what the cause is. That these atoms did
really act and alter the state of the contents of all the cells in the
glandular hair, which moved, was perfectly clear. But I hope next summer
to make out a good deal more...

LETTER 599. TO J.D. HOOKER. Down, May 14th [1861].

I have been putting off writing from day to day, as I did not wish to
trouble you, till my wish for a little news will not let me rest...

I have no news to tell you, for I have had no interesting letters for
some time, and have not seen a soul. I have been going through the
"Cottage Gardener" of last year, on account chiefly of Beaton's articles
(599/1. Beaton was a regular contributor to the "Cottage Gardener," and
wrote various articles on cross breeding, etc., in 1861. One of these
was in reply to a letter published in the "Cottage Gardener," May
14th, 1861, page 112, in which Darwin asked for information as to the
Compositae and the hollyhock being crossed by insect visitors. In the
number for June 8th, 1861, page 211, Darwin wrote on the variability of
the central flower of the carrot and the peloria of the central flower
in Pelargonium. An extract from a letter by Darwin on Leschenaultia,
"Cottage Gardener," May