﻿11) 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 (Jwiiperus 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 light 

 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 (8, 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 



