950 PLANTS REQUIRE NO SLEEP. 



vision and all the other senses are quiescent 

 that sleep walkers perform many extraordinary 

 feats of muscular and mental exertion, of which 

 they remember nothing afterwards. But this 

 inquiry cannot be further pursued at present. It 

 may, however, be observed, that nightmare is 

 owing to a temporary obstruction of the general 

 circulation, caused by overloading the stomach, or 

 by the intemperate use of spirituous liquors, both 

 of which prevent sound and refreshing sleep ; 

 while they induce a lethargic state of the system, 

 as shown by the torpor of the boa constrictor when 

 gorged with an enormous meal, by some savage 

 tribes, and by nearly all intemperate persons. 



As for plants, they require no sleep, because 

 they suffer no loss of their substance and vitality 

 by exercise, therefore, have nothing to do but to 

 grow. The drooping of the leaves which takes 

 place in a few of them when deprived of light, is 

 owing to a diminished circulation of sap through 

 their vessels, and is no more entitled to be re- 

 garded as sleep, than the folding up of the leaves 

 that takes place in some plants, under the 

 scorching influence of a burning sun, which causes 

 their fluids to be carried off by evaporation faster 

 than they are supplied by the soil. 



Nor must we confound the lethargy of hyber- 

 nating animals, (during which the temperature 

 falls to that of the surrounding medium, or nearly 

 so, and all the functions of life are arrested or 



