At noon on this day (8th) the
plants, after having been left before the north-east window for 5 h. 45 m.
and thus illuminated (though not brightly, as the sky was cloudy during the
whole time), were replaced in the dark cupboard, and at 3 P.M. the position
of the leaves was very little, if at all, altered, so that they are not
quickly affected by darkness; but by 10.15 P.M. all the leaves which had
faced the north-east sky during the 5 h. 45 m. of illumination stood
vertical, whereas those on the back of the plant retained their diurnal
position. On the following morning (9th) the leaves awoke as on the two
former occasions in the dark, and they were kept in the dark during the
whole day; at night a very few of them became vertical, and this was the
one instance in which we observed any inherited tendency or habit in this
plant to sleep at the proper time. That it was real sleep was shown by
these same leaves reassuming their diurnal position on the following
morning (10th) whilst still kept in the dark.
The pot was then (9.45 A.M. 10th) replaced, after having been kept for 36
h.
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