202 DISEASES OF TREES 



The white blotches consist of elements which have been con- 

 verted into cellulose, and which have become isolated by the 

 solution of the middle lamella. The yellowish parts, on the 

 other hand, reveal a form of decomposition of the cells which 

 is exceedingly like that due to P. igniarius > and which is cha- 

 racterised by the middle lamella persisting the longest. The 

 white patches are the first to be dissolved, and thus holes, sur- 

 rounded by very hard sides, are formed. When freely exposed 

 to the air the wood assumes a cinnamon brown colour, and is 

 replaced by a mass of firm brown hyphae. 



The large hoof-shaped annual sporophores are of a cinnamon 

 brown colour, and appear on the bark or on the spots previously 

 occupied by branches. They possess so little durability that 

 one but seldom meets with a perfect specimen. 



Should P. dryadens and P. igniarius simultaneously attack an 

 oak, and should their hyphae come into contact, a peculiar kind 

 of decomposition occurs along the line where the hyphae of the 

 two species meet. ' The wood becomes yellowish white, the 

 decomposition being similar in appearance to that which is 

 induced by P. igniarius alone. All the longer medullary rays, 

 however, are represented by snow-white bands, which, on being 

 investigated, are often found to consist of nothing but unaltered 

 starch-grains, while the cell-walls have been almost entirely 

 dissolved, or have been converted into cellulose. 



HYDNUM DIVERSIDENS l * 



A parasite is frequently met with on oaks and beeches whose 

 yellowish white sporophore takes the form of an incrustation or 

 bracket, and which is distinguished by the hymenium being 

 disposed on downward-directed spines of unequal length. The 

 hymenium, which is at first simple, periodically increases in 

 thickness by the hyphae growing through the last layer to form 

 a new hymenium. In the lower portion of the spines especially 

 this process is repeated five to eight times, the result being that 

 the spines increase greatly in thickness, and the hymenium 

 displays five to eight layers. 



In this case also the decomposition, which spreads from 



1 R. Hartig, Zersetsungsersckeinungen^ pp. 97 et seq.> and Table XII. 

 *[This is also British. ED.] 



