24 BULLETIN 1128, U. S. DEPARTMENT OF AGRICULTURE. 
logs sometimes have a decided brownish red stain on the sapwood. 
This is of no importance, because it does not occur on sawed lumber 
except so faintly as to be almost invisible. 
A very unsightly discoloration known as brown-stain (43, p. 
305-307), which, however, does not weaken the wood, often occurs 
on sugar pine, but is frequently not noticeable until the lumber has 
been finished. ‘This appears in the sapwood as a streaky, dirty, light 
to dark brown or brownish black discoloration, and may be super- 
ficial or very deep. It is quite striking against the faint yellowish 
white sapwood in finished lumber. The discoloration cccurs on 
green sap lumber upon exposure to the air and may appear during 
air drying or kiln drying. In the last instance it is known as kiln 
burn, but it does not differ from the brown-stain and is probably 
sometimes due to defective circulation in the kiln. Brown-stain is 
particularly bad in lumber cut in early spring. Hot, humid weather 
and poor circulation of air in the lumber piles favor the staining, 
while cool, dry weather and proper piling tend to prevent it. This 
brown stain is an oxidation process similar to the others, but whether 
it can be prevented by the hot-water treatment is doubtful, since the 
discoloration often extends deeply into the lumber. 
The wood of sugar pine in dead trees, standing or down, may be 
affected by a very brilliant orange stain which occurs in spots or as 
a solid color, but more often is seen as narrow to broad streaks 
parallel to the grain of the wood. It is found in both heartwood 
and sapwood. ‘The exact cause of this discoloration is unknown, but 
it is probably the result of chemical reaction, since no fungous 
mycelium has been found associated with it. While the wood is 
apparently not weakened, the presence of this stain indicates that 
the lumber came from dead trees, and it should be closely watched 
for signs of decay and insect borings. 
DISCOLORATIONS CAUSED BY FUNGI. 
From an economic standpoint by far the most important discolora- 
tions in wood are caused by fungi. Fungi are very simple plants 
which can not live on the simple food elements of the soil and air 
and build up complex organic matter, as is done by the green plants 
with which we are familiar, but must have organic matter already 
prepared in order to sustain life. This they find in the material 
built up by green plants; hence they may attack living plants, or 
dead portions of such plants, or any dead vegetable matter. Some 
live on animal matter, but these do not concern us. The develop- 
ment of fungi is dependent upon a supply of oxygen, of which there 
is always sufficient in the air, a certain degree of moisture, a suit- 
able range of temperature, and the necessary food substances. The 
maximum and minimum of these requirements vary widely with 
different fungi. 
The fungous plant consists of very fine threads (hyphz), which 
are invisible to the naked eye unless they occur in mass. Individual 
hyphe require magnification by a compound microscope. Collec-- 
tively, the hyphe are termed mycelium. The hyphe usually live in 
the tissues of the substance on which the fungus is growing. The 
fruiting bodies or sporophores, which vary in size from those so small 
as to be invisible to the naked eye except in a mass to others quite 
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