SECT. V. THE LIGNEOUS LAYERS. 33J 



united together, by something more than mere % 

 cellular tissue.* Such at least was the inference 

 of Senebier. But it is certain that the divergent 

 layers acquire a degree of consistence in their ma- 

 ture state, that can long resist the action of the 

 atmosphere. On the horizontal section of the 

 trunk of an Elm- tree that had been exposed for a 

 great length of time to the weather, and had begun 

 to be in a state of decay, I inspected minutely the 

 net-work in question, and found it to be evidently 

 composed of the remains both of concentric and 

 divergent layers. But the divergent layers are 

 composed of cellular tissue, which, if in its mature 

 state, it can long resist the action of the atmos- 

 phere, might for the same reason have long re- 

 sisted the action of the solvents employed by 

 Senebier ; and might still have been the only bond 

 of union between the concentric layers ; the sub- 

 stance which first disappears, and renders the net- 

 work visible, being the indurated parenchyma con- 

 tained within the cellular tissue, and assuming in 

 the Alburnum a soft and floccy appearance, rather 

 than the cellular tissue itself. 



The concentric layers therefore are composed of And both 

 longitudinal fibres, generally forming a net- work ; 

 and the divergent layers, of parallel threads r 

 fibres of cellular tissue, extending in a transverse 

 direction, and filling up the interstices of the net- 

 work ; the two sets of fibres being interwoven and 



* Phys. Veg. vol. i. p. 209. 

 VOL. I. Z 



