Fig. 157 Mimosa pudica: circumnutation and nyctitropic movement of main
petiole, traced during 34 h. 30 m.
On two other occasions the movement of the main petiole
[page 376]
was observed every two or three minutes, the plants being kept at a rather
high temperature, viz., on the first occasion at 77o - 81o F., and the
filament then described 2 ? ellipses in 69 m. On the second occasion, when
the temperature was 81o - 86o F., it made rather more than 3 ellipses in 67
m. therefore, Fig. 157, though now sufficiently complex, would have been
incomparably more so, if dots had been made on the glass every 2 or 3
minutes, instead of every hour or half-hour. Although the main petiole is
continually and rapidly describing small ellipses during the day, yet after
the great nocturnal rising movement has commenced, if dots are made every 2
or 3 minutes, as was done for an hour between 9.30 and 10.30 P.M. (temp.
84o F.), and the dots are then joined, an almost absolutely straight line
is the result.
To show that the movement of the petiole is in all probability due to the
varying turgescence of the pulvinus, and not to growth (in accordance with
the conclusions of Pfeffer), a very old leaf, with some of its leaflets
yellowish and hardly at all sensitive, was selected for observation, and
the plant was kept at the highly favourable temp.
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