north-east window; it bent very little towards it, as the hypocotyl which
was left free was rather old, and therefore not highly heliotropic. A
filament had been fixed to the midrib of one of the cotyledons, and the
movement of the whole seedling was traced during two days. The
circumnutation of the hypocotyl is quite insignificant compared with that
of the cotyledons. These rise up vertically at night and come into close
contact; so that they may be said to sleep. This seedling was so old that a
very small true leaf had been developed, which at night was completely
hidden by the closed cotyledons. On Sept. 24th, between 8 A.M. and 5 P.M.,
the cotyledons moved five times up and five times down; they therefore
described five irregular ellipses in the course of the 9 h. The great
nocturnal rise commenced about 4.30 P.M.

On the following morning (Sept. 25th) the movement of the same cotyledon
was again traced in the same manner during 24 h.; and a copy of the tracing
is here given (Fig. 25). The morning was cold, and the window had been
accidentally left open for a short time, which must have chilled the plant;
and this probably prevented it from moving quite as freely as on the
previous day; for it rose only four and sank only four times during the
day, one of the oscillations being very small. At 7.10 A.M., when the first
dot was made, the cotyledons were not fully open or awake; they continued
to open till about 9 A.M., by which time they had sunk a little beneath the
horizon: by 9.30 A.M. they had risen, and then they oscillated up and down;
but the upward and downward lines never quite coincided. At about 4.30 P.M.
the great nocturnal rise commenced. At 7 A.M. on the following morning
(Sept. 26th) they occupied nearly the same level as on the previous
morning, as shown in the diagram: they then began to open or sink in the
usual manner. The diagram leads to the belief that the great periodical
daily rise and fall does not differ essentially, excepting in amplitude,
from the oscillations during the middle of the day.