napaea,
according to Batalin, does not possess a pulvinus; and he informs us that a
gradation may be traced in the several species of the genus between these
two states of the petiole. Sida rhombifolia presents another peculiarity,
of which we have seen no other instance with leaves that sleep: for those
on very young plants, though they rise somewhat in the evening, do not go
to sleep, as we observed
Fig. 126. Sida rhombifolia: circumnutation and nyctitropic (or sleep)
movements of a leaf on a young plant, 9 ? inches high; filament fixed to
midrib of nearly full-grown leaf, 2 3/8 inches in length; movement traced
under a sky-light. Apex of leaf 5 5/8 inches from the vertical glass, so
diagram not greatly enlarged.
[page 323]
on several occasions; whilst those on rather older plants sleep in a
conspicuous manner. For instance a leaf (.85 of an inch in length) on a
very young seedling 2 inches high, stood at noon 9o above the horizon, and
at 10 P.M. at 28o, so it had risen only 19o; another leaf (1.4 inch in
length) on a seedling of the same height, stood at the same two periods at
7o and 32o, and therefore had risen 25o.
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