On the following morning
they were again flat and horizontal. the cotyledons of many other seedlings
were at the same time not in any way affected. Therefore this case seems
very different from that of ordinary sleep, and probably comes under the
head of epinasty, as is the case with the leaves of this plant according to
Kraus. The cotyledons are heliotropic, and so is the hypocotyl in a still
stronger degree.
Oxalis.--We now come to cotyledons provided with a pulvinus, all of which
are remarkable from the continuance of the nocturnal movements during
several days or even weeks, and apparently after growth has ceased. The
cotyledons of O. rosea, floribunda and articulata sink vertically down at
night and clasp the upper part of the hypocotyl. Those of O. Valdiviana and
sensitiva, on the contrary, rise vertically up, so that their upper
surfaces come into close contact; and after the young leaves are developed
these are clasped by the cotyledons. As in the daytime they stand
horizontally, or are even a little deflected beneath the horizon, they move
in the evening through an angle of at least 90o.
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