The Biology of Polyporus Pargamenus Fries 91 
panying cyto-hydrolytic enzyme. For instance, ligninase, 
called hadromase by Czapek (1899), designates the enzyme 
capable of «splitting lgnin; cellulase, the true cellulose- 
hydrolyzing ferment ; hemicellulase, the ferment hydrolyzing 
hemi-cellulose; and pectinase, an enzyme which hydroly ZeS 
into reducing sugars the pectinous substances, especially the 
middle larnellee of plants. All of these different enzymes and 
many others, when present, enact a definite role in the disso- 
lution of the woody substance. 
Recent investigations prove conclusively that, in order to 
accomplish the dissolution of the woody substance, each wood- 
destroying fungus secretes a number of different enzymes, 
each of which is so specialized that it acts only on certain 
individual substances or groups of related substances. Fur- 
thermore, these various enzymes may act simultaneously. 
In a word, enzyme action is the strategic center of vital 
activity. The chemical action induced by such agents causes 
a rapid dissolution of certain constituents of the cell-contents 
and the cell-walls of the wood, the ultimate product being a 
reduced, disintegrating mass which crumbles readily under 
the shghtest pressure. 
In all cases, regardless of how the decay proceeds or what 
constituents are removed from the wood, there is a momen- 
tous change in its physical character. This change is most 
strongly exemplified by the decrease in its specific gravity. 
In case the fungus has delignified the cell-walls of the wood, 
partial or complete collapse occurs, since it was through 
lignification of the fundamental cellulose wall originally that 
the essential element of strength was afforded. 
The ultimate effect of Polyporus pargamenus is to reduce 
the essential physical properties of the wood attacked and 
thereby lessen or completely destroy the utility and conse- 
quently the value of the timber. 
THe Decay or Yettow Biren Woop. 
Structure of Normal Wood.— Macroscopically the wood of 
yellow birch (Betula lutea Michx. f.) is heavy, hard, and 
strong, but not durable when exposed. The sapwood is a 
