The Story-Book of the Fields 



it is raw because it has not yet had the 

 preparation that is to turn it into the liquid 

 food of the plant. Hence we learn that the 

 rising sap is transported first of all to those 

 parts where the shoots are numerous and the 

 foliage abundant, and prefers the extremities of 

 the branches, where evaporation is most active. 

 We know that the exterior wood is the 

 youngest : it consists of cells, fibres and 

 vessels, the cavities of which are unconfined, 

 and whose walls are permeable. The in- 

 terior wood is older : its cells, fibres and 

 vessels are encrusted, obstructed, worn out 

 and useless. So the fluid makes its way 

 where circulation is possible, and no longer 

 penetrates where it is unable to pass. The 

 ascent of the sap occurs in the superficial and 

 recently formed layers. If a tree is cut 

 down at the season of the activity of the sap, 

 the outside layers will be damp, while the 

 inner wood is perfectly dry. In herbaceous 

 plants the ascent takes place throughout the 

 stem. This ascent stops in the winter because 

 of the absence of leaves, and acquires remark- 

 able activity at the return of spring. If 

 fruit trees have their branches lopped at this 

 season, they are said to bleed, for the ascending 

 fluid pours out through the openings of the 



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