Thus all
the leaflets, in those species which bear only 3 or 4 pairs, tend to form a
single packet, with their upper surfaces in contact, and their lower
surfaces turned outwards. Lastly, the main petiole rises at night, but with
leaves of different ages to very different degrees, namely some rose
through an angle of only 12o, and others as much as 41o.
Cassia calliantha.--The leaves bear a large number of leaflets, which move
at night in nearly the same manner as just described; but the petioles
apparently do not rise, and one which was carefully observed certainly fell
3o.
Cassia pubescens.--The chief difference in the nyctitropic
Fig. 155. Cassia pubescens: A, upper part of plant during the day; B, same
plant at night. Figures reduced from photographs.
movements of this species, compared with those of the former species,
consists in the leaflets not rotating nearly so much;
[page 372]
therefore their lower surfaces face but little outwards at night. The
petioles, which during the day are inclined only a little above the
horizon, rise at night in a remarkable manner, and stand nearly or quite
vertically.
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