﻿DECAYS AND DISCOLO RATIONS 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 0.) The wood for a 

 little distance around a pith-ray fleck may be darker than normal. 

 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 exceeding! v 



Fig. 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 nigra Linn., B. populifolia Marsh, 

 and B. papyrifera Marsh) they are found in abundance, but are 



