VIIL] THE CORTEX AND BARK OF TREES. 209 



" bark " of Cinchonas, and other economic processes, 

 depend on these matters. 



In anticipation of some points to be explained only 

 if these phenomena are understood, I may simply re- 

 mark here that, obviously, if some parasite attacks the 

 growing lips of the " callus " as it is trying to cover 

 up the wound, or if the cambium is injured below, the 

 pathological disturbances thus introduced will modify 

 the result : the importance of this will appear when 

 we come to examine certain disturbances which de- 

 pend upon the attacks of Fungi which settle on these 

 wounds before they are properly healed over. In con- 

 cluding this brief sketch of a large subject, it may be 

 noted that, generally speaking, what has been stated 

 of branches, &c., is also true of roots ; and it is easy 

 to see how the nibbling or gnawing of small animals, 

 the pecking of birds, abrasions, and numerous other 

 things, are so many causes of such wounds in the 

 forest. 



