1894 



THE MICROSCOPE. 



19 



spicuous, the medullary rays are much finer and greater 

 hi number consisting of more lines, the wood instead of 

 being in two rings, is in nine rings, the cambium layer 

 is narrower and the bark is much the same. 



The bark is in three layers, the external (epiphloeum) 

 which includes the corky layer, the middle or cellular 

 enA^eloj)e, and the liber. Next to the liber is the cam- 

 bium layer which always separates it from the wood and 

 it is in this that growth takes place. The epiphloeum 



usually consists of two or more cubical or tabular layers 

 and it is this which usually forms cork. Cork is by no 

 means confined to one tree but exists in greater or less 

 abundance in the bark of all exogenous stems. The mid- 

 dle layer is composed of cells and is more open than the 

 preceeding layer and often forms canals which have the 

 character of lactiferous vessels. This layer often forms 

 the greater part of the bark. The liber consists of cell- 

 ular vessels usually equaling in number the cells of the 



