EE EO Eee 
DECAYS AND DISCOLORATIONS IN AIRPLANE WOODS. 20 
are not subject to these pith-ray flecks, but a somewhat similar injury 
in western hemlock known as black check results from the work ot 
a different insect (/7). 
CHEMICAL DISCOLORATIONS. 
The sapwood of many species of wood is subject to discolorations, 
varying widely in appearance but fundamentally the same, which are 
the result of chemical action (3). Sapwood is rich in organic com- 
pounds and also contains certain soluble ferments which facilitate 
the oxidation of such compounds. Under favorable temperature con- 
ditions, for example, when green sapwood is exposed to the oxygen 
of the air, these ferments, known as oxidizing enzyms, act on the 
organic compounds in the sapwood. The result of their action, which 
is an oxidation process, is a discoloration of the sapwood, with the 
colored substance most noticeable upon microscopic examination in 
ue cells mainly concerned in the storage and transportation of 
ood. 
Hot, humid weather is most favorable for this staining. Cool, dry 
weather retards it or prevents it entirely. Logs immersed in water 
are not affected. Light is not necessary for this reaction, as it takes 
place just as readily in darkness. The stain is confined to the im- 
mediate surface layer, and the wood is not weakened. The most 
practical method of prevention, if this is considered necessary, is by 
dipping the green sap boards into boiling water for a few minutes 
as they come from the saw. 
HARDWOODS. 
Birch, maple, and cherry stain a reddish yellow or rusty color. 
The wood of alder becomes very intensely red or red-brown on freshly 
cut surfaces, often within an hour or so after the surface is exposed 
(40). In the case of red alder (Alnus oregona Nutt.), if the wood 
dries and remains white, the red color will appear upon the addition 
of water in the presence of air, provided the temperature is favor- 
able. A bluish stain often occurs in red gum (Liguidamber styraci- 
flua Linn.). - 
The European linden (77lia europaea, Linn.) is subject to a strik- 
ing discoloration (39), which probably also occurs on basswood 
in this country. When freshly sawed boards are so closely piled 
that they dry slowly, a more or less apparent dirty green color ap- 
pears in from 8 to 10 days. Under very favorable conditions the 
color is exceedingly bright and intense. The color varies between 
wide limits, from yellow-green or brown-green through all possible 
gradations to the purest moss green. Only the outer layers of the 
wood are colored. Usually the stain extends to a depth of one 
thirty-second of an inch or rarely to a depth of one-eighth of an inch. 
The staining, although it is the result of a chemical reaction (an iron- 
tannin reaction), is not dependent on temperature, since it occurs 
just as readily in winter asin summer. Too much moisture hinders 
the reaction, but a certain degree of moisture is essential. If the 
boards are dried quickly no staining results. 
SOFTWOODS. 
- Coniferous woods are not so commonly subject to this type of dis- 
coloration, but there are a few examples. The ends of incense-cedar 
