It rose up to its former level on the
following morning. The fourth and fifth leaves from the summit stood
horizontally during the day, and sank down at night only 38o. The sixth
leaf did not sensibly alter its position. The sinking movement is due to
the downward curvature of the petiole, no part of which exhibits any
structure like that of a pulvinus. Early on the morning of June 7th a
filament was fixed longitudinally to a young leaf (the third from the
summit, and 2 5/8 inches in length), and its movements were traced on a
vertical glass during 72 h., the plant being illuminated from above through
a skylight. Each day the leaf fell in a nearly straight line from 7 A.M. to
5 P.M., after which hour it was so much inclined downwards that the
movement could no longer be traced; and during the latter part of each
night, or early in the morning, the leaf rose. It therefore circumnutated
in a very simple manner, making a single large ellipse every 24 h., for the
ascending and descending lines did not coincide. On each successive morning
it stood at a less height than on the previous one, and this was probably
due partly to the increasing age of the leaf, and partly to the
illumination being insufficient; for although the leaves are very slightly
heliotropic, yet, according to Mr.
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