REPOSE, OR SLEEP. 97 



Do plants, it may be asked, sleep in consequence 

 cf the withdrawal of the light, or is this pheno- 

 menon more immediately connected with their 

 organism, that is, with some condition which 

 exists irrespective of the loss of the stimulus of 

 the light to which they are subjected during 

 the day ? According to the experiments of 

 Decandolle, by producing artificial day and 

 night, the natural periods of their sleeping and 

 waking may be reversed, and hence, at first 

 sight, we might be led to consider the with- 

 drawal of light as the sole cause of sleep. But, 

 then, how is the functional change to which we 

 have alluded to be accounted for ? And besides, 

 as we have said, some are nocturnal, sleeping 

 during the day, and awake during the night, 

 as anagallis, cereus, etc. ; moreover, it has been 

 ascertained that flowers, or the leaves of plants, 

 altogether excluded from the stimulus of light, 

 have their regular intervals of opening and 

 folding. Again, what definite end is to be 

 accomplished by this periodical repose ? To 

 man and the higher animals, sleep is " nature's 

 sweet restorer ;" but can it be said that it is so 

 to plants? It is easier to ask such questions than 

 to answer them. 



Let us pass, then, from a consideration of the 

 sleep of plants, to a few observations on the 

 sleep of animals, more particularly of the higher 

 orders. 



Sleep in man and the higher classes consists 

 in the periodical repose of the organs of the 

 senses, and the greater number of the intel- 



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