The Ascent of the Sap 



This force resides in the shoots, or rather 

 in the leaves. Every leaf is the seat of 

 vigorous evaporation, the object of which is 

 to eject from the plant the large amount of 

 water which has been needed to dissolve 

 in the ground the precious nutritive sub- 

 stances that have been absorbed, and to 

 transport them to the foliage. This evapora- 

 tion gives rise to a vacuum in the cells that 

 have ejected the water, which is at once filled 

 up from the neighbouring cells, which in 

 their turn receive the contents of the inferior 

 layers. A similar process goes on from cell 

 to cell, from fibre to fibre, from vessel to 

 vessel, at points farther and farther from 

 the evaporating surface, until it reaches the 

 extremities of the radicles, which by their 

 constant absorption replace the fluid that is 

 lost. It resembles the action of our pumps, 

 where the piston leaves a vacuum behind it, 

 immediately filled by the water in the pipe, 

 which receives it from the well. This fluid 

 that rises in every plant, being absorbed by 

 the spongioles of the radicles, and set in 

 motion by the evaporation of the leaves, is 

 called risifig sap or raw sap. It is said to 

 be rising because it proceeds from the bottom 

 to the top, from the roots to the branches ; 



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