Even with the 11-days' old
seedling the movement did not depend exclusively on the pulvinus, for the
blade where joined to the petiole was curved upwards, and this must be
attributed to unequal growth. Therefore the periodic movements of the
cotyledons of 'O. corniculata' depend on two distinct but conjoint actions,
namely, the expansion of the cells of the pulvinus and on the growth of the
upper part of the petiole, including the base of the blade.
Lotus Jacoboeus.--The seedlings of this plant present a case parallel to
that of Oxalis corniculata in some respects, and in others unique, as far
as we have seen. The cotyledons during the first 4 or 5 days of their life
do not exhibit any plain nocturnal movement; but afterwards they stand
vertically or almost vertically up at night. There is, however, some degree
of variability in this respect, apparently dependent on the season and on
the degree to which they have been illuminated during
[page 122]
the day. With older seedlings, having cotyledons 4 mm. in length, which
rise considerably at night, there is a well-developed pulvinus close to the
blade, colourless, and rather narrower than the rest of the petiole, from
which it is abruptly separated.
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