aggregation in leaves subjected for two hours to this gas and then
immersed in a solution of the carbonate of ammonia is much retarded, so
that a considerable time elapses before the protoplasm in the lower
cells of the tentacles becomes aggregated. In some cases, soon after
the leaves were removed from the gas and brought into the air, the
tentacles moved spontaneously; this being due, I presume, to the
excitement from the access of oxygen. These inflected tentacles,
however, could not be excited for some time afterwards to any further
movement by their glands being stimulated. With other irritable plants
it is known* that the exclusion of oxygen prevents their moving, and
arrests the movements of the protoplasm within their cells, but this
arrest is a different phenomenon from the retardation of the process of
aggregation just alluded to. Whether this latter fact ought to be
attributed to the direct action of the carbonic acid, or to the
exclusion of oxygen, I know not.
* Sachs, Traite de Bot. 1874, pp. 846, 1037. [page 229]
CHAPTER X.
ON THE SENSITIVENESS OF THE LEAVES, AND ON THE LINES OF TRANSMISSION OF
THE MOTOR IMPULSE.
Glands and summits of the tentacles alone sensitive Transmission of the
motor impulse down the pedicels of the tentacles, and across the blade
of the leaf Aggregation of the protoplasm, a reflex action First
discharge of the motor impulse sudden Direction of the movements of the
tentacles Motor impulse transmitted through the cellular tissue
Mechanism of the movements Nature of the motor impulse Re-expansion of
the tentacles.
We have seen in the previous chapters that many widely different
stimulants, mechanical and chemical, excite the movement of the
tentacles, as well as of the blade of the leaf; and we must now
consider, firstly, what are the points which are irritable or
sensitive, and secondly how the motor impulse is transmitted from one
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