14 
Mycologia 
the case of Trametes abietis the wood between the original areas 
of infection is finally attacked and broken down so that the whole 
mass of wood tissue eventually loses its firmness and is in large 
part destroyed. The same does not apply to the other fungi 
mentioned since the cells remain intact and sound between the 
diseased areas so far as can be detected by microchemical re- 
actions. 
The similarity between Stereum frustulosum and Hymeno- 
chaete rubiginosa in their manner of attack and effect on the 
wood is striking. Both are xerophytic fungi and attack decorti- 
cated wood which is sound or little decayed through the attacks 
of other fungi. The first is a perennial form reported on oak 
alone, so far as I have observed, the second an annual form found 
on oak, chestnut, and several other hosts. The first evidence of 
attack in both is in the formation of white areas which respond 
to the tests for cellulose. Subsequently the elements in these are 
in part digested and cavities are formed which in one stage of 
the disease are lined with a white layer of cellulose. The wood 
remains sound between the diseased areas and in the final stage 
the condition resulting is comparable to a honeycomb in which the 
cavities of the wood represent the chambers in the comb, and the 
tissue lying between, the walls of the chambers. The white lin- 
ing has entirely disappeared at this stage. 
From the preceding paragraph it follows that the decay in 
oak associated with H. rubiginosa is very similar, superficially, 
to that caused by Stereum frustulosum. Closer examination of 
the specimens at hand, however, has revealed a difference which 
may be of value in separating these two types of rot. The flecks 
caused by Stereum frustulosum are shorter and wider than those 
associated with H. rubiginosa. In radial view they appear as a 
rule from oval to elliptical in shape, while those of H. rubiginosa 
are narrow elliptical to long cylindrical. In the final stage of 
Stereum frustulosum the wood is much more porous, due to the 
large size of the cavities and the small spaces intervening.*® 
Chemical Changes in Oak Wood. — What has been said regard- 
15 The differences given above are much a matter of degree, however, and 
familiarity with the two types of decay is essential in making a reliable 
diagnosis. 
