dropped on the discs of leaves cause any inflection; but when they are
immersed in olive oil, they become strongly inflected; but to this
subject I shall have to recur. Oily substances are not digested by the
gastric juice of animals.
Starch. Rather large bits of dry starch caused well-marked inflection,
and the leaves did not re-expand until the fourth day; but I have no
doubt that this was due to the prolonged irritation of the glands, as
the starch continued to absorb the secretion. The particles were not in
the least reduced in size; [page 127] and we know that leaves immersed
in an emulsion of starch are not at all affected. I need hardly say
that starch is not digested by the gastric juice of animals.
Action of the Secretion on Living Seeds.
The results of some experiments on living seeds, selected by hazard,
may here be given, though they bear only indirectly on our present
subject of digestion.
Seven cabbage seeds of the previous year were placed on the same number
of leaves. Some of these leaves were moderately, but the greater number
only slightly inflected, and most of them re-expanded on the third day.
One, however, remained clasped till the fourth, and another till the
fifth day. These leaves therefore were excited somewhat more by the
seeds than by inorganic objects of the same size. After they
re-expanded, the seeds were placed under favourable conditions on damp
sand; other seeds of the same lot being tried at the same time in the
same manner, and found to germinate well. Of the seven seeds which had
been exposed to the secretion, only three germinated; and one of the
three seedlings soon perished, the tip of its radicle being from the
first decayed, and the edges of its cotyledons of a dark brown colour;
so that altogether five out of the seven seeds ultimately perished.
Radish seeds (Raphanus sativus) of the previous year were placed on
three leaves, which became moderately inflected, and re-expanded on the
third or fourth day. Two of these seeds were transferred to damp sand;
only one germinated, and that very slowly. This seedling had an
extremely short, crooked, diseased, radicle, with no absorbent hairs;
and the cotyledons were oddly mottled with purple, with the edges
blackened and partly withered.
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