water at other times, but no exact record of the effects produced was
kept; yet these cursory observations support the conclusions arrived at
in this chapter. A few of the long-headed tentacles, namely from one to
about six, were commonly inflected within half an hour after immersion;
as were occasionally a few, and rarely a considerable number of the
exterior round-headed tentacles. After an immersion of from 5 to 8 hrs.
the short tentacles surrounding the outer parts of the disc generally
become inflected, so that their glands form a small dark ring on the
disc; the exterior tentacles not partaking of this movement. Hence,
excepting in a few cases hereafter to be specified, we can judge
whether a solution produces any effect only by observing the exterior
tentacles within the first 3 or 4 hrs. after immersion.
Now for a summary of the state of the 173 leaves after an immersion of
3 or 4 hrs. in pure water. One leaf had almost all its tentacles
inflected; three leaves had most of them sub-inflected; and thirteen
had on an average 36.5 tentacles inflected. Thus seventeen leaves out
of the 173 were acted on in a marked manner. Eighteen leaves had from
seven to nineteen tentacles inflected, the average being 9.3 tentacles
for each leaf. Forty-four leaves had from one to six tentacles
inflected, generally the long-headed ones. So that altogether of the
173 leaves carefully observed, seventy-nine were affected by the water
in some degree, though commonly to a very slight degree; and
ninety-four were not affected in the least degree. This [page 140]
amount of inflection is utterly insignificant, as we shall hereafter
see, compared with that caused by very weak solutions of several salts
of ammonia.
Plants which have lived for some time in a rather high temperature are
far more sensitive to the action of water than those grown out of
doors, or recently brought into a warm greenhouse. Thus in the above
seventeen cases, in which the immersed leaves had a considerable number
of tentacles inflected, the plants had been kept during the winter in a
very warm greenhouse; and they bore in the early spring remarkably fine
leaves, of a light red colour. Had I then known that the sensitiveness
of plants was thus increased, perhaps I should not have used the leaves
for my experiments with the very weak solutions of phosphate of
ammonia; but my experiments are not thus vitiated, as I invariably used
leaves from the same plants for simultaneous immersion in water. It
often happened that some leaves on the same plant, and some tentacles
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