LETTER V. 



Look here, upon this picture." — Hamlet. 



August 18, 1854. 



My Dear Sons, 



1. Hitherto we have examined the Exogen in its 

 longitudinal or vertical aspect only. Let us now view 

 it in its transverse or horizontal, and in connection 

 with a tissue which is equally annual in its formation 

 as the wood or bark, but widely different from the 

 former, at least in the manner of its disposition and 

 growth. I mean the cellular tissue. This tissue may 

 be said to be the basis or matrix within which, or 

 rather through the midst of which the bundles of 

 woody tissue pass, and by means of which they are 

 bound and knit together^ The medullary rays, as 

 they are called, seen in the cross-cutting of a tree, 

 have their seat in this cellular tissue, and are in fact 

 nothing save a peculiar appearance given to it by the 

 mode in which the bundles traverse it. 



2. Viewed in this aspect, the additional facts fur- 

 nished by the Exogen will, if I mistake not, come out 



\ very favourably for our theory. 



