INJURIES INDUCED BY PLANTS 201 



POLYPORUS IGNIARIUS l * 



This is the parasite most frequently met with on the majority 

 of dicotyledonous trees. My investigations on its destructive 

 effects on wood have been conducted for the most part on the 

 oak. 



Infection may occur on branches or on bark-wounds, and the 

 mycelium spreads rapidly in the wood. At first the wood 

 assumes a deep brown colour, and this is succeeded by yellowish 

 white decomposition, which is the commonest kind of white- 

 rot in the oak. The yellowish white wood constantly becomes 

 lighter and softer, and resembles in its properties the cellulose 

 that is used in paper-making. The hyphse, which are at first 

 very strong and afterwards extremely delicate, completely fill 

 up the elements, and induce a form of decomposition which is 

 characterised by the inner layers of the walls being converted 

 into cellulose and dissolved, before the middle lamella, which 

 persists for a long time as a delicate skeleton, undergoes similar 

 changes. It will thus be seen that the process of decomposition 

 bears a close resemblance to that described under P. borealis. 

 The sporophores, which usually spring directly from bark that 

 is infested by the mycelium, are at first hemispherical, but 

 afterwards become more or less hoof-shaped. Although they are 

 familiar enough, it may be mentioned that they differ from 

 those of P. Hartigii) which they resemble in external appearance, 

 by exhibiting concentric zones, and frequently cracks as well, on 

 their upper surface, while internally the layers of pores are also 

 interrupted by the zones. 



POLYPORUS DRYADEUS 2 f 



This fungus of the oak produce^ a form of decomposition 

 in which oblong yellowish or white blotches occur, surrounded 

 by firm wood which displays the original colour of the duramen. 



1 R. Hartig, Zersetzungserscheinungen> pp. 114 et seq., and Tables XV. 

 .and XVI. 



2 Ibid., pp. 124 et seq., and Table XVII. 



*[One of the commonest fungi in Windsor Park and neighbourhood, 

 especially on old Beeches. ED.] 

 f [Common in Britain. ED.] 



