The evening rise began
after 4 P.M. in the same manner as before, and on the second morning it
again fell rapidly. The ascending and descending lines do not coincide, as
may be seen in the diagram. On the 30th a new tracing was made (not here
given) on a rather enlarged scale, as the apex of the leaf now stood 9
inches from the vertical glass. In order to observe more carefully the
course pursued at the time when the diurnal fall changes into the nocturnal
rise, dots were made every half-hour between 4 P.M. and 10.30 P.M. This
rendered the lateral zigzagging movement during the evening more
conspicuous than in the diagram given, but it was of the same nature as
there shown. The impression forced on our minds was that the leaf was
expending superfluous movement, so that the great nocturnal rise might not
occur at too early an hour.
Abutilon Darwinii (Malvaceae).--The leaves on some very young plants stood
almost horizontally during the day, and hung down vertically at night. Very
fine plants kept in a
[page 324]
large hall, lighted only from the roof, did not sleep at night for in order
to do so the leaves must be well illuminated during the day.
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