38 



COURSE OF THE SAP. 



PT. II. 



CHAPTEE II. 



COUESE OF THE SAP FROM THE ROOT TO THE LEAF^ 

 AND BACK TO THE ROOT. 



Coui'seof But, however mucli we may dispute on how tlie sap 



the upward j i i. 



th? whole ^ g^^^ i^^^ ^^^^ ivee^ we shall all agree that it does get in 

 of the wood. gQj-jrigj^Q^y . and, but for Dr. Lindley, I believe we should 

 all agree on the course which it then takes. 



The upward course of the sap is through the whole 

 woody part of the roots, stem, and branches of the tree. 

 This woody part has been hitherto divided by physiolo- 

 gists into two parts, the heart- wood or dead w^ood ; and 

 the alburnum or sap-wood ; that is, the unripe and out- 

 side rings, or latest deposits of wood around the stem. 

 It was considered that the heart- wood really was dead 

 wood, and that the upward course of the sap was 

 through the alburnum, or sap-wood, or latest rings of 

 wood only. In March, 1832, I remarked the stems of 

 some birch-trees, which I had cut down in the previous 

 November, bleeding from the heart-wood. I was not 

 then aw^are that Coulon had about this time observed 

 the same thing in cutting down some poplar-trees in 

 France. I afterwards satisfied myself, in various ways, 



