16 BULLETIN 1128, U. S. DEPARTMENT OF AGRICULTURE. 
of factors (52), but most important is a chemical reaction in which 
iron plays an important part. Timber is not weakened by this discol- 
oration, since the action is confined to the surface. 
In boards cut from red cedar (Juniperus virginiana Linn.) white 
streaks are frequently found mingling with the normal red heart- 
wood. Such streaks are the white sapwood, the mingling being due > 
to the irregular outline of the stem to which the heartwood con- 
forms or to layers which never change to heartwood. 
In Sitka spruce the heartwood has a light reddish tinge, slightly 
distinguishing it from the sapwood. Some trees of Sitka spruce, 
however, have a pronounced reddish or brownish pink heartwood, 
which is quite uniform throughout. The color difference is striking 
in a planed board or timber containing both heartwood of this kind 
and characteristic white sapwood. The same phenomenon undoubt- 
edly occurs, in red and white spruce, where it would be even more 
noticeable, since the heartwood in these species is normally as hight 
colored as the sapwood. This reddish heartwood is just as strong as 
wood of the usual color and can be safely utilized. The same condi- 
tion is reported as being quite common in the Himalayan spruce 
(Picea morinda Link) in India (16, 29). 
The brown heartwood of incense cedar (S, p. 22-24) and western 
red cedar often has a reddish to purplish tinge, varying in intensity 
even in the same piece, while in other trees it may be completely lack- 
ing. It is entirely without significance in relation to the strength 
of wood so affected. 
In certain softwoods color variations may be connected with 
changes in the rate of growth. In the heartwood of Douglas fir, 
which has a distinct reddish or orange-reddish hue, the reddish color 
may be strongly intensified in long regular bands. A careful exami- 
nation will show that this color change is confined to a definite group 
of annual rings, narrower than those on both sides or containing 
a greater proportion of summer wood. The brown heartwood of the 
cedars also varies in this way. The so-called “ yellow fir,” from the 
slowly grown, exceedingly narrow ringed outer layers of the old 
coast Douglas firs, is another example. The origin of such variations 
can be readily recognized, since the color is. confined to a definite 
group of annual rings. | 
Occasionally an apparent discoloration in heartwood may be due 
to the failure of the wood to change color uniformly during the 
transition from sapwood to heartwood. This has been noticed in 
white ash, Douglas fir, western red cedar, western larch (Larix oc- 
cidentalis Nutt.), and other woods. The sapwood of white ash is 
white or straw colored, while the heartwood is grayish brown, some- 
times with a reddish tinge. Hence, when the condition above men- 
tioned is found, the grayish brown heartwood will contain sharply 
delimited straw-yellow areas of various sizes and shapes. The wood 
is not weakened. How to avoid confusing this condition with the 
initial stages of white-rot will be considered later. 
Discoloration may be caused by dirt or dust. Surfaced or sanded 
white pine or sugar pine is sometimes found covered with tiny little 
grayish black streaks following the grain of the wood. A close ex- 
amination will show that this is due to deposition of dust in the 
numerous resin ducts. This is especially apparent against the almost 
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