CH. v.] THE SAP. 165 



forth by the sun, yet that the plant itself is put 

 forth by the moon ^. 



The sap, after ascending the stem, and being dis- 

 tributed along the various branches, is poured by 

 their vessels into their leaves and there undergoes 

 that elaboration, the phenomena of wliich have been 

 described in the last chapter. The sap vessels are 

 ramified from the wood of the branches along the 

 upper side of the leaf-stalks, are minutely subdi^'ided 

 so as to form a web resembling lace work, on their 

 superior sm'faces, and unite at the edge of the leaf 

 with equally minute vessels, forming a similar web 

 on then lower sm'faces. These fall into larger 

 vessels, which return the sap along the under side 

 of the leaf-stalks into vessels traversing the inner 

 bark of the branches, stem, and roots, and the sap 

 is found to be converted, during its elaboration in 

 the leaves, into the peculiar juices of the plant. The 

 limpid insipid sap has been converted into the 

 austere Gallic acid and tannin of the oak; the 

 acrid perfumed oil of the lemon ; the insipid gum 

 of the cheriy ; the starchy matter of the potato, 

 and the pimgent resin of the pine tribe. 



In its descent in trees and shrubs it deposits 



between the bark and the wood that juice, known as 



cambium, from which the year's increase or enlarged 



growth is obtained, and a superfluous store is depo- 



^ Deut. xxxiii. 14. 



