getting the leaves into a proper position. That water should produce no
effect might have been anticipated, as otherwise the leaves would have
been excited into movement by every shower of rain.
[Gum arabic. Solutions of four degrees of strength were made; one of
six grains to the ounce of water (one part to 73); a second rather
stronger, yet very thin; a third moderately thick, and a fourth so
thick that it would only just drop from a pointed instrument. These
were tried on fourteen leaves; the drops being left on the discs from
24 hrs. to 44 hrs.; generally about [page 78] 30 hrs. Inflection was
never thus caused. It is necessary to try pure gum arabic, for a friend
tried a solution bought ready prepared, and this caused the tentacles
to bend; but he afterwards ascertained that it contained much animal
matter, probably glue.
Sugar. Drops of a solution of white sugar of three strengths (the
weakest containing one part of sugar to 73 of water) were left on
fourteen leaves from 32 hrs. to 48 hrs.; but no effect was produced.
Starch. A mixture about as thick as cream was dropped on six leaves and
left on them for 30 hrs., no effect being produced. I am surprised at
this fact, as I believe that the starch of commerce generally contains
a trace of gluten, and this nitrogenous substance causes inflection, as
we shall see in the next chapter.
Alcohol, Diluted. One part of alcohol was added to seven of water, and
the usual drops were placed on the discs of three leaves. No inflection
ensued in the course of 48 hrs. To ascertain whether these leaves had
been at all injured, bits of meat were placed on them, and after 24
hrs. they were closely inflected. I also put drops of sherry-wine on
three other leaves; no inflection was caused, though two of them seemed
somewhat injured. We shall hereafter see that cut off leaves immersed
in diluted alcohol of the above strength do not become inflected.
Olive Oil. drops were placed on the discs of eleven leaves, and no
effect was produced in from 24 hrs. to 48 hrs. Four of these leaves
were then tested by bits of meat on their discs, and three of them were
found after 24 hrs. with all their tentacles and blades closely
inflected, whilst the fourth had only a few tentacles inflected. It
will, however, be shown in a future place, that cut off leaves immersed
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