The Biology of Polyporus Pargamenus Fries 157 
constantly from the wood as fast as it is attacked by the 
advancing fungus. 
(3) In the decay of coniferous woods the formation of 
humic substances similar to those studied here is very small 
in quantity as compared with those arising in the decay of 
dicotyledonous woods. 
(4) In wood free from fungous attack the formation of 
the brown decomposition products is dependent mainly upon 
the concurrence of three factors: (a) the presence of dead 
cells, (b) an optimum supply of moisture, and (¢c) a supply 
of oxygen sufficient to promote oxidation. 
(5) The partially decomposed material of woody plants 
forms a particularly vague and indefinite group of sub- 
stances containing all the non-volatile products of fungal, 
enzymic, and oxidative actions on the plant residues. The 
resultant humic substances are exceptionally resistant to 
chemical reagents. 
(6) It is evident that the cell contents and certain other 
substances, particularly the hemicellulose, xylan (wood 
gum), that originally were combined with the cellulose to 
constitute the cell-wall furnish the formative material which, 
through oxidation upon the entrance of air and the presence 
of water, coagulates to thick drops and gives rise to the 
decomposition products which ultimately infiltrate certain 
portions of the wood, causing them to appear as blackish 
zones. 
(7) In the wood of the pignut hickory the hemicellulose, 
zylan, is destroyed early in the progress of the decay. In the 
early stages of the decomposition of the wood the wood gum 
apparently is the substance which gives rise to most of the 
humic substance. 
(8) By the action of a strong oxidizing reagent on fresh 
sapwood a brown humic substance can be prepared arti- 
ficially, which is essentially like that occurring naturally in 
dicotyledonous woods, whether in wounded areas of living 
trees, dead wood, or as the result of their decay by Polyporus 
pargamenus and other wood-rotting fungi. 
