CH. I. 



BY THE SURFACE OF THE ROOTS. 



13 



comprehensive as Sir Hiimpliry'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 bv the roots.'* Its course The course 



oftheTrea- 



upward is throuo;h the whole of the wood, heart-wood tisewiiigo, 



^ ^ ' with the 



as well as sap-wood, of the root, the stem, and the theVoor 

 branches. It thence passes through the insides of the theT^od 

 leaves and buds, and returns through their outsides into and hack ' 



by the bark 



the bark, and descends again to the roots. From the to the root, 

 ascending sap the growth in elongation of the stem 

 and branches takes place ; and from the descending sap 

 the growth in girthing of them, and also the growth in 

 elongation of the roots. 



But I imagine that, besides this vertical or longitu- 

 dinal flow of the sap between the roots and the 

 branches, there is also a horizontal or transverse 

 circulation between the heart- wood and bark ; and that 

 the joint elaboration of these two saps is essential to the 

 formation of the new annual growth in girthing. This 

 consists of a new sheath of wood, deposited outside the 

 last year's growth of wood, over the entire surface of 

 the stem, branches, and roots ; and also of a new sheath 



* Even tMs first principle is quite contrary to the opinions 

 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. 



