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 puie 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 ty|)es of 

 timber-diseases shall be described ? Of course the 

 limits of a popular book aie 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 appaiently similar *' cankers" which 

 are caused by other variations in the environment — 

 the atmosphere and weather generally. 



It would need many chapters to place the readei au 

 cotirant with the chief results of what is known of 



