752 , 



very complicated movements, without our being able to discover the 

 slightest trace of a nervous system. 



" The cells of vegetables are contractile ; and exciting agents act 

 upon them directly, without the intervention of any intermediate 

 body. The vascular tissue, being highly elastic, readily yields to 

 the motion impressed on the cellular tissue. 



" We may regard the cellular tissue of the sensitive plant as being 

 erectile in its nature. When it is in a state of active dilatation, the 

 plant is turgid, and its leaves are spread out; when the tissue is in a 

 contracted condition, the plant closes its leaflets and lowers its pe- 

 tioles. 



" In a state of active dilatation, the fluids of the plant fill the cells 

 of the lower surfaces, and maintain them in a state of turgescence. 



" In a state of contraclibility the fluids, being less abundant, leave 

 the cells of the upper surfaces hanging down and pressing upon 

 the lower surface. 



" In this way we may explain the normal diurnal and nocturnal 

 movements of the sensitive plant. In the day time, when the plant 

 is exposed to the light, the fluids are attracted towards the cuticle, 

 and there maintain a constant equilibrium, the fresh supplies replac- 

 ing those which had passed off" by evaporation. If this equilibrium 

 is interrupted by a touch, by cold, or by wounds, the circulation is 

 disturbed ; the fluids suddenly abandon the cells of the upper sur- 

 faces, dilate the vessels by the reaction, and a state of contractibility 

 is the consequence. 



" At the approach of evening, the fluids being less strongly propel- 

 led towards the superior surfaces, a condensation of the tissues en- 

 sues ; the plant contracts, and in the night the phenomenon attains 

 its maximum of intensity, ceasing gradually at the return of day. 

 Darkness opposes no obstacle to the diurnal state of sleeping leaves : 

 it even serves to maintain this state, and tends to keep the leaves 

 displayed. 



" When plants are placed in darkness, in a cool cellar, where the 

 air is loaded witii humidity, their waking state may endure for many 

 days. 



" If plants in a waking state are suddenly shifted from warm to 

 cool air, they assume their sleeping state, if there is a considerable 

 difference in the temperature. 



" If such plants are watered when in their waking state in a dark 

 place, they immediately enter upon their sleeping state, which, how- 

 ever, does not last long. 



