, 1877, p. 95), on the gradations in the
Leguminosae between suba?rial and subterranean cotyledons.
[page 111]
time they are expanded almost horizontally. The circumnutating movement is
thus at least partially periodic, no doubt in connection, as we shall
hereafter see, with the daily alternations of light and darkness. The
cotyledons of several plants move up so much at night as to stand nearly or
quite vertically; and in this latter case they come into close contact with
one another. On the other hand, the cotyledons of a few plants sink almost
or quite vertically down at night; and in this latter case they clasp the
upper part of the hypocotyl. In the same genus Oxalis the cotyledons of
certain species stand vertically up, and those of other species vertically
down, at night. In all such cases the cotyledons may be said to sleep, for
they act in the same manner as do the leaves of many sleeping plants. This
is a movement for a special purpose, and will therefore be considered in a
future chapter devoted to this subject.
In order to gain some rude notion of the proportional number of cases in
which the cotyledons of dicotyledonous plants (hypogean ones being of
course excluded) changed their position in a conspicuous manner at night,
one or more species in several genera were cursorily observed, besides
those described in the last chapter.
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