prevent, as far as possible, the secretion, with its dissolved animal
matter, being wholly lost.
It has already been remarked that plants growing in a state of nature
have the margins of their leaves much more strongly incurved than those
grown in pots and prevented from catching many insects. We have seen
that insects washed down by the rain from all parts of the leaf often
lodge within the margins, which are thus excited to curl farther
inwards; and we may suspect that this action, many times repeated
during the life of the plant, leads to their permanent and well-marked
incurvation. I regret that this view did not occur to me in time to
test its truth.
It may here be added, though not immediately [page 381] bearing on our
subject, that when a plant is pulled up, the leaves immediately curl
downwards so as almost to conceal the roots, a fact which has been
noticed by many persons. I suppose that this is due to the same
tendency which causes the outer and older leaves to lie flat on the
ground. It further appears that the flower-stalks are to a certain
extent irritable, for Dr. Johnson states that they bend backwards if
rudely handled. *
Secretion, Absorption, and Digestion. I will first give my observations
and experiments, and then a summary of the results.
[The Effects of Objects containing Soluble Nitrogenous Matter.
(1) Flies were placed on many leaves, and excited the glands to secrete
copiously; the secretion always becoming acid, though not so before.
After a time these insects were rendered so tender that their limbs and
bodies could be separated by a mere touch, owing no doubt to the
digestion and disintegration of their muscles. The glands in contact
with a small fly continued to secrete for four days, and then became
almost dry. A narrow strip of this leaf was cut off, and the glands of
the longer and shorter hairs, which had lain in contact for the four
days with the fly, and those which had not touched it, were compared
under the microscope and presented a wonderful contrast. Those which
had been in contact were filled with brownish granular matter, the
others with homogeneous fluid. There could therefore be no doubt that
the former had absorbed matter from the fly.
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