192 LE'AVES FROM THE BOOK OF NATURE. 



or otherwise suffering, cannot sleep, but keep their leaves 

 open and erect all night long, until they perish. Other 

 plants close their leaves during the day, and awake from 

 their slumbers at night, while a few even droop and clasp 

 the stem, as if seeking support in its strength, whenever 

 the sky is overcast and a storrn is threatening. 



This peculiar faculty of sleep stands in immediate con- 

 nection with the general power of certain leaves to move, 

 either upon coming in contact with other bodies, or, ap- 

 parently, in spontaneous motion. All the above-mentioned 

 mimosas fold up their leaves, when merely touched ; first 

 one little leaflet will be closed, then another, until the 

 whole leaf proper, with its delicate footstalk, droops down 

 and clasps the stem of the parent. If the plant be very 

 irritable and nervousness is here found to be in propor- 

 tion to good health the other leaves will follow the ex- 

 ample, until the whole little plant plays, to use a Virginia 

 phrase, '"possum." and looks, for all the world, as if it 

 were asleep. The oxalis of this continent requires several 

 successive strokes to produce the same effect, and the 

 robinia, our locust, which sleeps at night, must be violently 

 shaken. The common wild lettuce, also, shows a great 

 irritability, and, curiously enough, only when the plant is 

 in flower. Upon being touched, the leaves contract be- 

 neath, and force out, above, a milky juice, with which they 

 soon become covered. 



The so-called spontaneous movements of leaves and 

 other parts of plants arise mostly, though not always, 

 from their general tendency to turn towards the light. 

 Little is as yet known with accuracy of this interesting 



