On the following morning,
[page 302]
the petioles diverged before it was light. The hypocotyl is slightly
sensitive, so that if rubbed with a needle it bends towards the rubbed
side. In the case of Lepidium sativum, the petioles of the cotyledons of
young seedlings diverge during the day and converge so as to touch each
other during the night, by which means the bases of the tripartite blades
are brought into contact; but the blades are so little raised that they
cannot be said to sleep. The cotyledons of several other cruciferous plants
were observed, but they did not rise sufficiently during the night to be
said to sleep.
Githago segetum (Caryophylleae).--On the first day after the cotyledons had
burst through the seed-coats, they stood at noon at an angle of 75o above
the horizon; at night they moved upwards, each through an angle of 15o so
as to stand quite vertical and in contact with one another. On the second
day they stood at noon at 59o above the horizon, and again at night were
completely closed, each having risen 31o. On the fourth day the cotyledons
did not quite close at night.
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