I 



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del attention to the phenomenon of the sleep of 

 plants. I found them the same in the steppes, 

 where no irregularity of the ground interrupted 

 the view of the horizon. It appears, that, ac- 

 customed during the day to an extreme brilli- 

 ancy of light, the sensitive and other legumi- 

 nous plants with thin and delicate leaves are 

 affected in the evening by the smallest decline 

 in the intensity of the sun's rays ; so that night 

 begins for the vegetables, there as with us, be- 

 fore the total disappearance of the solar disk* 

 But why, under a zone where there is scarcely 

 any twilight, do not the first rays of the sun 

 stimulate the leaves with so much more force, 

 as the absence of light must have rendered 

 them more irritable ? Does the humidity de- 

 posited on the parenchyma by the cooling of 

 the leaves, which is the effect of the nocturnal 

 radiation, prevent perhaps the action of the first 

 rays of the Sun ? In our climates, the legumi- 

 nous plants with irritable leaves awake during 

 the twilight of the morning, before the sun ap- 

 pears. 



