The pulvinated cotyledons of some individuals of Mimosa
pudica and Lotus Jacobaeus made only a single oscillation, whilst those of
other individuals moved twice up and down in the course of 24 hours; so it
was occasionally with the cotyledons of Cucurbita ovifera, which are
destitute of a pulvinus. The movements of pulvinated cotyledons are
generally larger in extent than those without a pulvinus; nevertheless some
of the latter moved through an angle of 90o. There is, however, one
important difference in the two sets of cases; the nocturnal movements of
cotyledons without pulvini, for instance, those in the Cruciferae,
Cucurbitaceae, Githago, and Beta, never last even for a week, to any
conspicuous degree. Pulvinated cotyledons, on the other hand, continue to
rise at night for a much longer period, even for more than a month, as we
shall now show. But the period no doubt depends largely on the temperature
to which the seedlings are exposed and their consequent rate of
development.
[Oxalis Valdiviana.--Some cotyledons which had lately opened and were
horizontal on March 6th at noon, stood at night vertically up; on the 13th
the first true leaf was formed, and was embraced at night by the
cotyledons; on April 9th, after an interval of 35 days, six leaves were
developed, and yet the cotyledons rose almost vertically at night.
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