It is therefore
probable that this sleep-like movement, which occurs only when the ground
is dry, is an adaptation against the loss of moisture.
A bush about 4 feet in height, a native of Chili, which was thickly covered
with leaves, behaved very differently, for during the day it never closed
its leaflets. On July 6th the earth in the small pot in which it grew
appeared extremely dry, and it was given a very little water. After 21 and
22 days (on the 27th and 28th), during the whole of which time the plant
did not receive a drop of water, the leaves began to droop, but they showed
no signs of closing during the day. It appeared almost incredible that any
plant, except a fleshy one, could have kept alive in soil so dry, which
resembled the dust on a road. On the 29th, when the bush was shaken, some
leaves fell off, and the remaining ones were unable to sleep at night. It
was therefore moderately watered, as well as syringed, late in the evening.
On the next morning (30th) the bush looked as fresh as ever, and at night
the leaves went to sleep. It may be added that a small branch while growing
on the bush was enclosed, by means of a curtain of bladder, during 13 days
in a large bottle half full of quicklime, so that the air within must have
been intensely dry; yet the leaves on this branch did not suffer in the
[page 338]
least, and did not close at all during the hottest days.
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