ASCENDING SAP 109 



fiber to fiber, from duct to duct, a similar transfer 

 takes place at points farther and farther away from 

 the evaporating surface, until the tip-ends of the 

 rootlets are reached, where a continuous absorption 

 makes good the loss of moisture by evaporation. 

 The process reminds one somewhat of the working 

 of our pumps, in which the piston leaves behind it 

 a void that is immediately filled by the water in the 

 pipe, which in its turn gets water from the bottom 

 of the well. This liquid which ascends in every 

 plant, absorbed by the spongioles of the rootlets 

 and put in motion by the evaporation from the leaves, 

 is called ascending sap, or crude sap. The sap is 

 called ascending because it passes from below up- 

 ward, from the roots to the branches ; and it is called 

 crude because it has not yet undergone the prepara- 

 tion that will turn it into the nutritive liquid of the 

 plant. Thus we have learned our first lesson, 

 namely: ascending sap is carried especially to those 

 parts of the plant where buds are numerous, where 

 leaves abound; it seeks by preference the ends of 

 the branches, where evaporation is most active. 



"We know that the surface wood is the newest; 

 it is formed of cells, fibers, and ducts whose cavities 

 are free and whose walls are permeable. The in- 

 terior wood is older; its cells, fibers, and ducts are 

 encrusted, stopped up, decrepit, out of use. The 

 liquid accordingly makes its way where circulation 

 is possible, and ceases to flow where the passage is 

 obstructed. That is to say, the ascent of the sap 

 takes place through the sap-wood and chiefly through 



