204 TIMBER AND SOME OF ITS DISEASES, [chap, 



Hgnified, and for the most part very thin and yielding, 

 and retain their living contents. For the rest, we 

 may neglect details and refer to the illustration for 

 further particulars. The tissue in question is marked 

 by Sj c, hb in the figure, and is called phloem or bast. 



A word or two as to the functions of the cortex, 

 though the subject properly demands much longer 

 discussion. It may be looked upon as especially the 

 part through which the valuable substances formed in 

 the leaves are passing in various directions to be used 

 where they are wanted. When we reflect that these 

 substances are the foods from which everything in the 

 tree — new cambium, new roots, buds, flowers, and 

 fruit &c. — are to be constructed, it becomes clear that 

 if any enemy settles in the cortex and robs it of 

 these substances, it reduces not only the general 

 powers of the tree, but also — and this is the point 

 which especially interests us now — its timber-produc- 

 ing capacity. In the same way, anything which cuts 

 or injures the continuity of the cortical layers results 

 in divexting the nutritive substances into other 

 channels A very large class of phenomena can be 

 explained if these points are understood, which would 

 be mysterious, or at least obscure, otherwise. 



Having now sketched the condition of this cortical 

 jacket when the branch or stem is still young, it will 



