LETTER XIX. 



" All knowledge is to be referred to use and action." 



Lord Bacon. 



" Be aye stickin' in a tree, Jock ; it'll growe whaun ye're sleepin'." 



Sir Walter Scott, Bart. 



September 20, 1855. 



My Dear Sons, 



1. If my theorj^ be a sound one, it should be worth 

 something. It should supply a reasonable answer to 

 the question — Cui bono ? 



2. One use it will clearly serve — that of explaining 

 various phenomena occurring in trees, and that of 

 solving sundry questions presenting themselves in con- 

 nection with trees — such questions as those relating 

 to their age and size, the very variable duration of 

 trees of the same species or of different species — and 

 such phenomena as the unequal growth of trees on 

 different sides, the winding course, or the strange 

 bundling and plaiting of the woody fibres in the trunk 

 of some trees, the vigorous state of many trees, even 

 after the trunk is in a state of decay and quite hollow, 

 the existence of roots in the chasms, and of birds' 



