and then the distinction, as might be expected, becomes very doubtful,
and at last disappears. But as in all, except the simplest, cases the
state of the leaves simultaneously immersed for an equal length of time
in water and in the solutions will be described, the reader can judge
for himself.]
CARBONATE OF AMMONIA.
This salt, when absorbed by the roots, does not cause the tentacles to
be inflected. A plant was so placed in a solution of one part of the
carbonate to 146 of water that the young uninjured roots could be
observed. The terminal cells, which were of a pink colour, instantly
became colourless, and their limpid contents cloudy, like a mezzo-tinto
engraving, so that some degree of aggregation was almost instantly
caused; but no further change ensued, and the absorbent hairs were not
visibly affected. The tentacles [page 142] did not bend. Two other
plants were placed with their roots surrounded by damp moss, in half an
ounce (14.198 ml.) of a solution of one part of the carbonate to 218 of
water, and were observed for 24 hrs.; but not a single tentacle was
inflected. In order to produce this effect, the carbonate must be
absorbed by the glands.
The vapour produces a powerful effect on the glands, and induces
inflection. Three plants with their roots in bottles, so that the
surrounding air could not have become very humid, were placed under a
bell-glass (holding 122 fluid ounces), together with 4 grains of
carbonate of ammonia in a watch-glass. After an interval of 6 hrs. 15
m. the leaves appeared unaffected; but next morning, after 20 hrs., the
blackened glands were secreting copiously, and most of the tentacles
were strongly inflected. These plants soon died. Two other plants were
placed under the same bell-glass, together with half a grain of the
carbonate, the air being rendered as damp as possible; and in 2 hrs.
most of the leaves were affected, many of the glands being blackened
and the tentacles inflected. But it is a curious fact that some of the
closely adjoining tentacles on the same leaf, both on the disc and
round the margins, were much, and some, apparently, not in the least
affected. The plants were kept under the bell-glass for 24 hrs., but no
further change ensued. One healthy leaf was hardly at all affected,
though other leaves on the same plant were much affected. On some
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