44 
COURSE OF TIIE SAP. 
[Part II. 
Course of the 
upward sap 
through the 
whole of the 
wood. 
CHAP. II. 
COURSE OF THE SAP FROM THE ROOT TO THE LEAF, 
AND BACK TO THE ROOT. 
But, however much we may dispute on how the 
sap gets into the tree, we shall all agree that it 
does get in somehow; 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 physiologists into two parts, the heart- 
wood or dead wood; and the alburnum or sap- 
wood, that is, the unripe and outside 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 
aware that Coulon had about this time observed 
