In our observations on the
circumnutation of leaves, some were selected which were rather too young,
so that they continued to diverge or sink downwards whilst their movements
were being traced. This may be seen in the diagrams (Figs. 98 and 112, pp.
232 and 249) representing the circumnutation of the young leaves of
Acanthus mollis and Pelargonium zonale. Similar cases were observed with
Drosera. The movements of a young leaf, only 3/4 inch in length, of Petunia
violacea were traced during four days, and offers a better instance (Fig.
111, p. 248) as it diverged during the whole of this time in a curiously
zigzag line with some of the angles sharply acute, and during the latter
days plainly circumnutated. Some young leaves of about the same age on a
plant of this Petunia, which had been laid horizontally, and on another
plant which was left upright, both being kept in complete darkness,
diverged in the same manner for 48 h., and apparently were not affected by
apogeotropism; though their stems were in a state of high tension, for when
freed from the sticks to which they had been tied, they instantly curled
upwards.
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