cabbage Decoction of grass leaves.
When, in 1860, I first observed Drosera, and was led to believe that
the leaves absorbed nutritious matter from the insects which they
captured, it seemed to me a good plan to make some preliminary trials
with a few common fluids, containing and not containing nitrogenous
matter; and the results are worth giving.
In all the following cases a drop was allowed to fall from the same
pointed instrument on the centre of the leaf; and by repeated trials
one of these drops was ascertained to be on an average very nearly half
a minim, or 1/960 of a fluid ounce, or .0295 ml. But these measurements
obviously do not pretend to any strict accuracy; moreover, the drops of
the viscid fluids were plainly larger than those of water. Only one
leaf on the same plant was tried, and the plants were collected from
two distant localities. The experiments were made during August and
September. In judging of the effects, one caution is necessary: if a
drop of any adhesive fluid is placed on an old or feeble leaf, the
glands of which have ceased to secrete copiously, the drop sometimes
dries up, especially if the plant [page 77] is kept in a room, and some
of the central and submarginal tentacles are thus drawn together,
giving to them the false appearance of having become inflected. This
sometimes occurs with water, as it is rendered adhesive by mingling
with the viscid secretion. Hence the only safe criterion, and to this
alone I have trusted, is the bending inwards of the exterior tentacles,
which have not been touched by the fluid, or at most only at their
bases. In this case the movement is wholly due to the central glands
having been stimulated by the fluid, and transmitting a motor impulse
to the exterior tentacles. The blade of the leaf likewise often curves
inwards, in the same manner as when an insect or bit of meat is placed
on the disc. This latter movement is never caused, as far as I have
seen, by the mere drying up of an adhesive fluid and the consequent
drawing together of the tentacles.
First for the non-nitrogenous fluids. As a preliminary trial, drops of
distilled water were placed on between thirty and forty leaves, and no
effect whatever was produced; nevertheless, in some other and rare
cases, a few tentacles became for a short time inflected; but this may
have been caused by the glands having been accidentally touched in
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