98 THE VEGETABLE WORLD. 
Primrose (C@nothera) has similar properties, and like the Trefoil 
forms during the night a sort of cradle for the reception of the 
leaves. On the contrary, the genus Sida and the Lupinus reverse 
their leaves. On the other hand, many of the Mallows roll their 
leaves into the form of a coronet. The Vetch, the Sweet Pea, the 
Broad Bean, rest their leaves during the night one against the 
other, and seem to sleep. 
This strange sleep of plants vaguely recalls to us the sleep of 
i animals. Inits 
sleep the leaf 
seems, by its 
disposition, to 
approach _ the 
&\.\ age of infancy. 
“ It folds itself 
: up, nearly as 
it lay folded in the bud before 
it opened, when it slept the 
lethargic sleep of winter, 
sheltered under the robust 
and hardy scales, or shut up 
in its warm down. We may 
say that the plant seeks every 
night to resume the position 
which it occupied in its early 
days, just as the animal rolls 
itself up, lying as if it lay mn 
its mother’s bosom. 
What is the cause of the 
phenomenon which we desig- 
nate the sleep of plants? It occurs in all hygrometrical conditions 
Fig. 124.—Closed leaves of Oxalis. 
of the atmosphere, and the hours during which it affects them ise 
not influenced by any change of temperature. De Candolle sup- 
posed that the absence of light was the direct cause of the pheno 
menon. To assure himself of this, he subjected plants whose leaves 
are disposed to sleep, to the action of artificial light, furnished by 
two lamps which were, when united, equal to five-sixths of daylight. 
The results were very varied. “When I exposed the Sensitive 
