49 



only quote his opinions as quoted by 

 others. I regret this, as, from them, 

 he appears to be the most acute of all 

 physiologists. 



That the growth in the girthing or 

 diameter of trees is a downward growth, 

 that is, from the descending sap, seems 

 clear from this :— If a ring of bark is 

 taken olF round the stem or branch of a 

 tree, so as to intercept the return of 

 the sap between the wood and the bark, 

 as long as the tree or branch lives it 

 will continue to increase in girthing or 

 diameter above the ring, but not below 

 it ; and when such a branch is sawed in 

 two, lengthways, each additional annual 

 layer may be counted above the ring, 

 but none below it. But if the growth in 

 diameter was deposited from the upward 

 sap, the parts of a branch below the ring 

 would be more favourably situated for it 

 than the parts above the ring. 



A new innermost layer of bark (liber) 



D 



