1/3200 of a grain (.0202 mg.). Fourteen of these were strongly
inflected within 2 hrs., and some of them within 15 m.; three out of
the eighteen were only slightly affected, having twenty-one, nineteen,
and twelve tentacles in- [page 157] flected; and one was not at all
acted on. By an accident only fifteen, instead of eighteen, leaves were
immersed at the same time in water; these were observed for 24 hrs.;
one had six, another four, and a third two, of their outer tentacles
inflected; the remainder being quite unaffected.
The next experiment was tried under very favourable circumstances, for
the day (July 8) was very warm, and I happened to have unusually fine
leaves. Five were immersed as before in a solution of one part to
131,250 of water (1 gr. to 300 oz.), so that each received 1/4800 of a
grain, or .0135 mg. After an immersion of 25 m. all five leaves were
much inflected. After 1 hr. 25 m. one leaf had all but eight tentacles
inflected; the second, all but three; the third, all but five; the
fourth; all but twenty-three; the fifth, on the other hand, never had
more than twenty-four inflected. Of the corresponding five leaves in
water, one had seven, a second two, a third ten, a fourth one, and a
fifth none inflected. Let it be observed what a contrast is presented
between these latter leaves and those in the solution. I counted the
glands on the second leaf in the solution, and the number was 217;
assuming that the three tentacles which did not become inflected
absorbed nothing, we find that each of the 214 remaining glands could
have absorbed only 1/l027200 of a grain, or .0000631 mg. The third leaf
bore 236 glands, and subtracting the five which did not become
inflected, each of the remaining 231 glands could have absorbed only
1/1108800 of a grain (or .0000584 mg.), and this amount sufficed to
cause the tentacles to bend.
Twelve leaves were tried as before in a solution of one part to 175,000
of water (1 gr. to 400 oz.), so that each leaf received 1/6400 of a
grain (.0101 mg.). My plants were not at the time in a good state, and
many of the leaves were young and pale. Nevertheless, two of them had
all their tentacles, except three or four, closely inflected in under 1
hr. Seven were considerably affected, some within 1 hr., and others not
until 3 hrs., 4 hrs. 30 m., and 8 hrs. had elapsed; and this slow
action may be attributed to the leaves being young and pale. Of these
nine leaves, four had their blades well inflected, and a fifth slightly
so. The three remaining leaves were not affected. With respect to the
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