147 



scarce touch the leaf of a vigorons sensitive plant so 

 ightly as not to make it clo^e. The large rib which 

 uns along its middle, is as an hin-e on which the two 

 ves of the leaf move, when they turn upon being- 

 touched, till they stand erect, and by that means meet 

 e another. The slightest touch gfves this motion to 

 elcaf; if a little harder, it gives the same motion 

 the leaf opposite. If the touch be still rougher the 

 whole arrangement of leaves on the same rib 'close in 

 the same manner. If it be stronger still, the rib itself 

 loves upward toward the branch on which it grows 

 if the touch be yet more rough, the very branches 

 innk up toward the main stem. The motion which 

 has the greatest effect of all others upon it, is the 



f 'haking one. Winds and heavy rain also caus- tfsis 

 lant to close its leaves, but not gentle showers the 

 ontraction being caused by the agitation of the wind 

 antt^ the strokes given by the large drops. 



The natural shutting and opening o f its leaves at 

 night and morning, are not so fixed as not to be va 

 riablc by many circumstances. In August a sensitive" 

 plant was carried in a pot into a dark cave. The 

 shaking in the carriage shut up its leaves, so that they 

 did not open for four and twenty hours; and whea 

 :hey dfd open, they closed no more for three days am! 

 nights. Being then brought again into the open air 

 they recovered their natural motions, shutting at ni-ht 

 and opening in the morning, as regular!/ as ever 

 Mile m the cave, it was as much affected by the 

 touch as in the open air. 



By this and many experiments it appears, that it is 

 not the light that opens these plants, nor the darkness 

 which shuts them. Neither is it owing to the increase 

 >f heat or cold. Indeed great heat will alh-ct them a 

 Jittle, but not in any considerable degree. Concern- 

 ing the real cause, we m ; ,y form man/coiijcclures, but 

 .{nothing certain can be 'known. 



Nearly related to the sleep of plants, is that which 

 Linnaeus called the awaking O f flowers. The flowers 

 plants, after they are once opened, continue 

 ii 2 



