16 
Mycologia 
It is of interest in this connection to compare Stereum hir- 
sutum Fr. with Hymeuocliacte rubiginosa in its method of attack 
on wood and the chemical changes involved (Ward, 1898). This 
form is not so exacting as to its host as H. rubiginosa, but grows 
readily on oak, willow, horse-chestnut, pine, and other hosts. The 
fungus, while usually saprophytic, may spread from dead wood 
into the trunk and in such cases shows marked preference for 
the sap wood. This does not apply with H. rubiginosa; it is 
found uniformly on fallen, decorticated wood and no preference 
is shown for sap wood. The mycelium of Stereum hirsutum 
attacks all the elements in the diseased tissue with equal ease and 
localized areas of distintegration are not formed. The whole 
mass of tissue eventually succumbs and a general decay of the 
wood results. In both fungi the first evidence of decay is one of 
delignification. The tertiary la}’ers are first reduced to cellulose, 
followed successively by the secondary and primary layers, and 
the swollen cellulose matrix is then consumed, layer by layer. In 
the case of 5 '. hirsutum, the primary lamella is not attacked until 
the last, and before it succumbs the tertiary and secondary layers 
have usually entirely disappeared. This is in marked contrast to 
the decay caused by H. rubiginosa, where the middle lamella dis- 
appears as soon as lignin reduction is complete and before cellulose 
digestion has taken place. While closely related botanically, 
marked differences occur in the decay caused by the two forms. 
The superficial type of decay at the periphery of the wood noted 
above has likewise been observed in connection with Stereum 
frustulosum}'’ The possibility still remains, however, that this 
may have been caused by the mycelium of another fungus as in 
the case of the form described in this paper. Pure cultures are 
necessary to decide this point. 
Between the cavities the wood appears sound in both forms of 
decay. The pockets may enlarge occasionally and coalesce, and 
larger pockets thus arise. The mycelial strands accompanying 
the decay described here were likewise described by Hartig in 
connection with Stereum frustulosum. Both forms apparently 
employ the same method of attack and bring about a similar prog- 
ress of decay in the wood. 
1" Hartig, Th., loc. cit., page 19. 
