subsequent absorption is, perhaps, one of the most striking cases. But
it is not really more remarkable than the digestion of meat, which is
dissolved by this secretion in the same manner and by the same stages
as by gastric juice. The secretion dissolves bone, and even the enamel
of teeth, but this is simply due to the large quantity of acid
secreted, owing, apparently, to the desire of the plant for phosphorus.
In the case of bone, the ferment does not come into play until all the
phosphate of lime has been decomposed and free acid is present, and
then the fibrous basis is quickly dissolved. Lastly, the secretion
attacks and dissolves matter out of living seeds, which it sometimes
kills, or injures, as shown by the diseased state [page 270] of the
seedlings. It also absorbs matter from pollen, and from fragments of
leaves.
The seventh chapter was devoted to the action of the salts of ammonia.
These all cause the tentacles, and often the blade of the leaf, to be
inflected, and the protoplasm to be aggregated. They act with very
different power; the citrate being the least powerful, and the
phosphate, owing, no doubt, to the presence of phosphorus and nitrogen,
by far the most powerful. But the relative efficiency of only three
salts of ammonia was carefully determined, namely the carbonate,
nitrate, and phosphate. The experiments were made by placing
half-minims (.0296 ml.) of solutions of different strengths on the
discs of the leaves, by applying a minute drop (about the 1/20 of a
minim, or .00296 ml.) for a few seconds to three or four glands, and by
the immersion of whole leaves in a measured quantity. In relation to
these experiments it was necessary first to ascertain the effects of
distilled water, and it was found, as described in detail, that the
more sensitive leaves are affected by it, but only in a slight degree.
A solution of the carbonate is absorbed by the roots and induces
aggregation in their cells, but does not affect the leaves. The vapour
is absorbed by the glands, and causes inflection as well as
aggregation. A drop of a solution containing 1/960 of a grain (.0675
mg.) is the least quantity which, when placed on the glands of the
disc, excites the exterior tentacles to bend inwards. But a minute
drop, containing 1/14400 of a grain (.00445 mg.), if applied for a few
seconds to the secretion surrounding a gland, causes the inflection of
the same tentacle. When a highly sensitive leaf is immersed in a
solution, and there is ample time for absorption, the 1/268800 of a
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