position 5 and all leaves elevate themselves on the 
foot-stalk during their exposure to the solar light, 
and as it were move towards the sun. 
This effect seems in a great measure dependent 
upon the mechanical and chemical agency of light 
and heat. Bonnet made artificial leaves, which, 
when a moist sponge was held under the lower 
surface, and a heated iron above the upper surface, 
turned exactly in the same manner as the natural 
leaves. This, however, can be considered only as 
a very rude imitation of the natural process. 
What Linnaeus has called the sleep of the leaves, 
appears to depend wholly upon the suspension of 
the action of light and heat, and on the operation 
of moisture. 
This singular but constant phenomenon had 
never been scientifically observed, till the attention 
of the botanist of Upsal was fortunately directed 
to it. He was examining particularly a species of 
lotus, in which four flowers had appeared during 
the day, and he missed two in the evening ; by 
accurate inspection, he soon discovered that these 
two were hidden by the leaves which had closed 
round them. Such a circumstance could not be 
lost upon so acute an observer. He immediately 
took a lantern, went into his garden, and witnessed 
a series of curious facts before unknown. All the 
simple leaves of the plants he examined, had an 
arrangement totally different from their arrange- 
ment in the day : and the greater number of them 
were seen closed or folded together. 
The sleep of leaves is, in some cases, capable of 
being produced artificially. Decandole made this 
