i;o TIMBER AND SOME OF ITS DISEASES. [CHAP. 



caused by its ally : probably none but an expert could 

 distinguish between them, though the differences are 

 clear when the histology is understood. 



Polyporus fulvus is remarkable because its hyphre 

 destroy the middle-lamella, and thus isolate the 

 tracheides in the timber of firs ; Polyporus borealis 

 also produces disease in the timber of standing 

 Conifers ; Polyporus igniarius is one of the commonest 

 parasites on trees such as the oak, &c., and produces 

 in them a disease not unlike that due to the last form 

 mentioned ; Polyporus dryadeus also destroys oaks, 

 and is again remarkable because its hyphse dissolve 

 the middle-lamella. 



With reference to the two fungi last mentioned it 

 will be interesting to describe a specimen in the 

 Museum of Forest Botany in Munich, since it seems 

 to have a possible bearing on a very important ques- 

 tion of biology, viz. the action of soluble ferments. 



It has already been stated that some of these tree- 

 killing fungi excrete ferments which attack and dissolve 

 starch-grains, and it is well known that starch-grains 

 are stored up in the cells of the medullary rays found 

 in timber. Now, Polyporus dryadeus and P. igniarius 

 are such fungi ; their hyphae excrete a ferment which 

 completely destroys the starch-grains in the cells of 

 the medullary rays of the oak, a tree very apt to be 



