The Biology of Polyporus Pargamenus Fries 191 
in the decay of different woods by this fungus are much more 
dependent upon the dissimilar structure of the respective 
woods than has been generally supposed. 
The results of the microscopic study of the decay of five 
woods of diverse structure, of the macroscopic study of the 
decay in twenty-eight other species of wood, indicate that the 
decay progresses to varying extents in different woods before 
reaching completion and that the decay of any given species 
approaches completion long before the w oody “substance is 
entirely destroyed. The ratio between the amounts of chemi- 
cally resistant by-products accumulated in the woody tissue 
and the potential food supply still remaining available for 
assimilation by the fungus automatically constitutes itself 
an index of the completion of the decay. 
The anatomical and microchemical observations on the 
decays of the five woods studied indicate that the vegetative 
mycelium of Polyporus pargamenus secretes diastatic, pro- 
teolytic, and cytohydrolytic enzymes, among the latter being 
pectinase, cellulase, and hgninase. 
The metabolic by-products most frequently encountered in 
wood decayed by Polyporus pargamenus are the extremely 
chemically resistant brown humic products which infiltrate 
portions of the wood, causing them to appear as brownish dis- 
colored areas, or which more often collect in narrow zones 
between the decayed and undecayed portions, causing the 
wood at this point to appear as a blackish zone of varying 
thickness. These zones are not constant in position since 
they keep pace with the advance of the decay in any part of 
the stem and ultimately disappear upon its completion within 
that part. 
The partially decomposed material of wocdy plants forms 
a particularly vague and indefinite group of substances con- 
taining all the non-volatile products of fungal, enzymic, and 
oxidative actions on the plant residues. The physical appear- 
ance and chemical composition of the brown humic by- 
products of decomposition vary greatly according to the 
extent to which they have been reduced. The chief character- 
istic of this series of degradation products of plant tissues is 
