The above amount of movement of the cotyledons is only temporary,
lasting with plants kept in a warm greenhouse from four to six days; how
long it would last with seedlings growing out of doors we do not know.
Raphanus sativus.--In the middle of the day the blades of the cotyledons of
10 seedlings stood at right angles to their hypocotyls, with their petioles
a little divergent; at night the blades stood vertically, with their bases
in contact and with their petioles parallel. Next morning, at 6.45 A.M.,
whilst it was still dark, the blades were horizontal. On the following
night they were much raised, but hardly stood sufficiently vertical to be
said to be asleep, and so it was in a still less degree on the third night.
Therefore the cotyledons of this plant (kept in the greenhouse) go to sleep
for even a shorter time than those of the cabbage. Similar observations
were made, but only during a single day and night, on 13 other seedlings
likewise raised in the greenhouse, with the same result.
The petioles of the cotyledons of 11 young seedlings of Sinapis nigra were
slightly divergent at noon, and the blades stood at right angles to the
hypocotyls; at night the petioles were in close contact, and the blades
considerably raised, with their bases in contact, but only a few stood
sufficiently upright to be called asleep.
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