Chap. I.] BY THE SURFACE OF THE ROOTS. 
15 
subject, that one cannot adopt a single opinion 
without opposing many, held by minds, perhaps, 
as clear and comprehensive as Sir Humphrey’s. 
It is, then, to save the reader’s time if I lay 
down as certain what better men have doubted 
or controverted; or if I use the words, “ I think 
this,” or “ I think that,” in stating other people’s 
opinions. 
The sap is absorbed by the roots.* Its course 
upward is through the whole of the wood, heart- 
wood as well as sap-wood, of the root, the stem, 
and the branches. It thence passes through the 
insides of the leaves and buds, and returns 
through their outsides into the bark, and 
descends again to the roots. From the ascend¬ 
ing sap the growth in elongation of the stem 
and branches takes place, and from the descend¬ 
ing sap the growth in girthing of them, and also 
the growth in elongation of the roots. 
But I imagine that, besides this vertical or 
longitudinal flow of the sap between the roots 
and the branches, there is also a horizontal or 
* Even this first principle is quite contrary to the opi¬ 
nions of the mass of physiologists, ancient and modern. 
Priestley, Senebier, De Saussure, Liebig, &c., think the 
more head, the more root it will feed. I think the more 
root, the more head it will feed. 
The course of 
the Treatise will 
go, with the sap, 
from the root, 
through the 
wood to the 
leaf, and back 
by the bark to 
the root. 
