172 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



oak-timber thus attacked, and the medullary rays 

 of which appeared as glistening white plates. These 

 plates consist of nearly pure starch : the hyphae have 

 destroyed the cell-walls, but left the starch intact. It 

 is easy to suggest that the two ferments acting to- 

 gether exert (with respect to the starch), a sort of in- 

 hibitory action one on the other ; but it is also obvious 

 that this is not the ultimate explanation, and one 

 feels that the matter deserves further investigation. 



It now becomes a question What other types of 

 timber-diseases shall be described ? Of course the 

 limits of a popular book are too narrow for anything 

 approaching an exhaustive treatment of such a sub- 

 ject, and nothing has as yet been said of several other 

 diseases due to crust-like fungi often found on decaying 

 stems, or of others due to certain minute fungi which 

 attack healthy roots. Then there is a class of diseases 

 which commence in the bark or cortex of trees, and 

 extend thence into the cambium and timber : some of 

 these " cankers," as they are often called, are proved 

 to be due to the ravages of fungi, though there is 

 another series of apparently similar " cankers " which 

 are caused by other variations in the environment 

 the atmosphere and weather generally. 



It would need many chapters to place the reader au 

 courant with the chief results of what is known of 



