But between 7.15 and 10.15
P.M. the line consisted of a succession of steps, the cause of which we
could not understand; it was, however, manifest that the movement was no
longer a simple descending one.
Siegesbeckia orientalis (Compositae).--Some seedlings were raised in the
middle of winter and kept in the hot-house; they flowered, but did not grow
well, and their leaves never showed any signs of sleep. The leaves on other
seedlings raised in May were horizontal at noon (June 22nd), and depended
at a consi-
[page 385]
derable angle beneath the horizon at 10 P.M. In the case of four youngish
leaves which were from 2 to 2 ? inches in length, these angles were found
to be 50o, 56o, 60o, and 65o. At the end of August when the plants had grown
to a height of 10 to 11 inches, the younger leaves were so much curved
downwards at night that they might truly be said to be asleep. This is one
Fig. 162. Nicotiana glauca: shoots with leaves expanded during the day, and
asleep at night. Figures copied from photographs, and reduced.
of the species which must be well illuminated during the day in order to
sleep, for on two occasions when plants were kept all day in a room with
north-east windows, the leaves did not sleep at night.
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