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The Biology of Polyporus Pargamenus Fries 149 
examination shows that they are caused by brown infiltra- 
tions in the cell-walls and lumina of the cells, these infiltra- 
tions often becoming so abundant that they exude into the 
lumina of the cells, particularly the vessels, and occlude 
these completely. (Plate XXVIII, Figs. 1 and 2, and 
Plate XXIX.) This brown substance usually collects in a 
blackish zone or layer between two adjoining areas in differ- 
ent stages of decay. If it should happen that for some reason 
the progress of the decay be indefinite and retarded the 
brown product may appear merely as an unlocalized brown 
discoloration in the wood. When seen in mass it is respon- 
sible for the dark coloration mentioned above. At the time 
of its formation the brown product is a liquid, but, upon 
further decomposition, it changes to a brown, amorphous 
brittle substance, frequently becoming more or less cracked 
after dessication. 
Chemical Origin of the Brown Decomposition Product.— 
The physical appearance and chemical composition of the 
brown by-product of decomposition varies greatly according 
to the extent to which it has become chemically altered: ‘Tn 
the earlier stages of the decay much of this decomposition 
product is soluble in and can be extracted from finely divided 
wood with a 5 per cent solution of potassium hydroxide. If 
the potash solution be neutralized with dilute hydrochloric 
acid a reddish-brown gelatinous precipitate of humic acid 
is formed slowly, which gradually settles to. the bottom. 
When dried the residue resembles the brown masses seen 
in many of the wood elements.. Von Schrenk (19007, p. 37) 
describes the decomposition product as follows: ‘“ In mass 
it is reddish-brown, soft, tasteless and odorless, insoluble in 
alcohol, ether, chloroform, acetone, turpentine, etc., but very 
soluble in alkahes, KOH, NaHPO,, ete., and can be repre- 
cipitated from such solutions by acids.” Because of its pecu- 
har physical and chemical properties the substance has been 
classed among the ‘“ humus compounds.” As was stated 
earlier in connection with the description of the decay of 
individual woods by Polyporus pargamenus, the hyphe fre- 
