but when viewed as a transparent object under the microscope, minute
specks of light were transmitted, and this was not the case with the
unaffected parts of the same leaves. These effects, however, merely show
that the secreted fluid is highly injurious or poisonous to leaves; for
nearly the same effects were produced in from one to two days on various
kinds of young leaves, not only by artificial pancreatic fluid, prepared
with or without thymol, but quickly by a solution of thymol by itself.
On one occasion leaves of Corylus were much discoloured by being kept for
eighteen hours in pancreatic fluid, without any thymol. With young and
tender leaves immersion in human saliva during rather warm weather, acted
in the same manner as the pancreatic fluid, but not so quickly. The
leaves in all these cases often became infiltrated with the fluid.
Large leaves from an ivy plant growing on a wall were so tough that they
could not be gnawed by worms, but after four days they were affected in a
peculiar manner by the secretion poured out of their mouths. The upper
surfaces of the leaves, over which the worms had crawled, as was shown by
the dirt left on them, were marked in sinuous lines, by either a
continuous or broken chain of whitish and often star-shaped dots, about 2
mm. in diameter. The appearance thus presented was curiously like that
of a leaf, into which the larva of some minute insect had burrowed. But
my son Francis, after making and examining sections, could nowhere find
that the cell-walls had been broken down or that the epidermis had been
penetrated. When the section passed through the whitish dots, the grains
of chlorophyll were seen to be more or less discoloured, and some of the
palisade and mesophyll cells contained nothing but broken down granular
matter. These effects must be attributed to the transudation of the
secretion through the epidermis into the cells.
The secretion with which worms moisten leaves likewise acts on the
starch-granules within the cells. My son examined some leaves of the ash
and many of the lime, which had fallen off the trees and had been partly
dragged into worm-burrows. It is known that with fallen leaves the
starch-grains are preserved in the guard-cells of the stomata. Now in
several cases the starch had partially or wholly disappeared from these
cells, in the parts which had been moistened by the secretion; while it
was still well preserved in the other parts of the same leaves.
Sometimes the starch was dissolved out of only one of the two
guard-cells. The nucleus in one case had disappeared, together with the
starch-granules. The mere burying of lime-leaves in damp earth for nine
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