The Biology of Polyporus Pargamenus Fries 161 
again be precipitated. The humic acids comprise substances 
thrown down as brown collodial precipitates by mineral acids 
or alkaline extracts of humus. The humie acids (their chem- 
ical composition is insufliciently known), containing pos- 
sibly 59 to 63 per cent C., 4.4 to 4.6 per cent H, and 35 to 
36 per cent O, are easily dissolved in alkalies and repre- 
cipitated from their solutions by stronger mineral acids. If 
they are withdrawn from acid soils or from ground decayed 
wood with alkalies or NH; and precipitated with HCl, 
voluminous, gelatinous substance is obtained which, in dry- 
ing, forms a brown or black amorphous mass. The humic 
acids are separated from their solution by freezing, in the 
form of a dark-colored powder, which gradually passes over 
again into solution. 
Products similar to these are obtained in a large number 
of decompositions of the carbohydrates, both simple and com- 
plex. Trusov (1915) reports experiments in which it was 
found that the humification of various organic compounds 
consists of both chemical and biological processes, woody sub- 
stances being humified by chemical compounds and fungi, 
albumin by ‘biological processes alone, and substances con- 
taining tannin and chlorophyll by chemical processes alone. 
He found that the process of humification was aided by good 
aeration and relatively high temperatures. The time neces- 
sary for complete humification of the various compounds 
varied, albumin requiring a longer period than lignin sub- 
stances containing tannic acid and chlorophyll. Starch was 
humified very slowly. Water extracts of undecomposed 
woody substances were very active in humus formation. 
Humus was not formed from proteids from substances con- 
taining tannic acid and chlorophyll, and was formed from 
lignin only when that substance decomposed together with 
albumin. 
While it is true that the tendency in the decay of organic 
matter is toward simpler compounds and ultimately to a few 
simple compounds or the elements, the material known as 
soil organic matter is in the transition stage from the com- 
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