DECAYS AND DISCOLORATIONS IN AIRPLANE WOODS. 21 
shaped areas, which on the tangential or slash-grain face and the 
radial or edge-grain face of a board appear as brown streaks, usually 
running in a vertical direction. (Figs. 8 and 9.) The wood for a 
little distance around a pith-ray fleck may be darker than normai. 
This is particularly so in poplars or cottonwoods (Populus spp.). 
On the whole, the injuries are not at all serious, having no noticeable 
effect on the strength of the wood unless the flecks are exceedingly 
Fic. 7.—Slash-grain or tangential surface of a tulip-poplar board, showing stain and 
bird’s-eye caused by sapsuckers. One-third natural size. (Courtesy of the U. S. 
Biological Survey.) 
numerous. Only in the cherries (Prunus spp.) may a weakening 
be expected, for there the affected wood tissues are broken down, 
while in the other woods they are but little distorted. Furthermore, 
the presence of pith-ray flecks is usually hard to detect in the heart- 
wood of cherries. The color of the heartwood differs but little from 
the color of the pith-ray flecks. 
Pith-ray flecks are found in all the common poplars or cotton- 
woods, birches, maples, cherries, basswood, and many others, but 
there is considerable variation in their abundance on different closely 
related species. For example, these flecks are very common in soft 
maple, while they are rather infrequent in hard maple. In river, 
gray, and paper birch (Betula negra Linn., B. populifolia Marsh, 
and B. papyrifera Marsh) they are found in abundance, but are 
