Chap. VII. SLEEP OF LEAVES. 337 



or even quite, closed during the day. But twigs cut from this 

 hush, with their ends standing in water, or wholly immersed in 

 it, or kept in damp air under a bell-glass, opened their leaves 

 though exposed to a blazing sun; whilst those on the plant 

 in the ground remained closed. The leaves on this same plant, 

 after some heavy rain, remained open for two days ; they then 

 became half closed during two days, and after an additional 

 day were quite closed. This plant was now copiously watered, 

 and on the following morning the leaflets were fully ex- 

 panded. The other plant growing in a pot, after having been 

 exposed to heavy rain, was placed before a window in the Labo- 

 ratory, with its leaflets open, and they remained so during the 

 daytime for 48 h. ; but after an additional day were half closed. 

 The plant was then watered, and the leaflets on the two following 

 days remained open. On the third day they were again half 

 closed, but on being again watered remained open during the 

 two next days. Prom these several facts we may conclude that 

 the plant soon feels the want of water ; and that as soon as this 

 occurs, it partially or quite closes its leaflets, which in their 

 then imbricated condition expose a small surface to evaporation. 

 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 ir 

 (he 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 diiring 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 sufler in the 



