210 SLEEP OF FLAM'S. 



likewise follow the sun in its course; a clover- 

 field is a familiar instance of this. 



Of all leaves those of pinnated leguminous 

 plants are found most affected by light, inso- 

 much that it appears, in several cases, the sole 

 cause of their expansion, for when it is with- 

 drawn they fold over each other, or droop, 

 as if dying; and this is called by Linnaeus the 

 Sleep of Plants, who has a dissertation on the 

 subject in his Amoenitates Academicce. The 

 term Sleep may not really be so hyperbolical 

 as at first sight it seems, for the cessation of 

 the stimulus of light, and of the consequent 

 restrained position, of the leaves, may be use- 

 ful to the vegetable constitution, as real sleep 

 is to the animal. Another purpose is answered 

 by the nocturnal folding of some leaves, that 

 they shelter their flowers from the dew, the 

 advantage of which we shall explain hereafter. 



Some pinnated leaves display a more ex- 

 traordinary sensibility, not merely to light, 

 but to the touch of any extraneous body, 

 or to any sudden concussion, as those of 

 Mimosa sensitiva, and puclica, O.vaiis seii- 

 :iiJivci, and Sjnithuf scns/tiva^ Ad, Hori. 



