This bush
exhibited in a striking manner the evil effects of the leaves not being
allowed to assume at night their normal dependent position; for had they
all been prevented from doing so, assuredly every single leaf on the bush
would have been utterly killed by this exposure of only 30 m. The leaves
whilst sinking downwards in the evening twist round, so that the upper
surface is turned inwards, and is thus better protected than the outwardly
turned lower surface. Nevertheless, it was always the upper surface which
was more blackened than the lower, whenever any difference could be
perceived between them; but whether this was due to the cells near the
upper surface being more tender, or merely to their containing more
chlorophyll, we do not know.
Melilotus officinalis.--A large pot with many plants, which had been kept
during the winter in the greenhouse, was exposed during 5 h. at night to a
slight frost and clear sky. Four leaves had been pinned out, and these died
after a few days; but so did many of the free leaves. Therefore nothing
certain could be inferred from this trial, though it indicated that the
horizontally extended leaves suffered most.
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