4 



BULLETIN 1140, U. S. DEPARTMENT OF AGRICULTURE, 



distributed by seasons of exposure except in the case of those cut in 

 1918, of which there are only three, all that could be obtained. The 

 basis for this class is insufficient. The cull percentage shows a steady 

 increase and the percentage of total trees with merchantable volume 

 a steady decrease except in the 1918 trees. This points to a sufficient 

 basis for the other classes. Then, too, during the course of the field 

 work the similarity in condition between trees exposed for the same 

 number of seasons was quite apparent. 



Figure 1, which is a diagrammatic smoothed curve based on Table 

 1, illustrates the rate of deterioration of the down timber. 



ZOO 



SO 



^80 



I 70 



/O — 



1 ] I 



mm 



Fig. 1. 



O / 2 3 4 5 6 7 



<S£:/?&oa/s' or exposure: 



-Diagrammatic smoothed curve, illustrating the rate of deterioration of felled 

 western yellow pine. 



CAUSES OF DETERIORATION. 



In Table 1 sap-stain is not considered a defect. While this dis- 

 coloration does degrade the lumber, discolored wood can still be used 

 for a variety of purposes. In this region blue-stain caused by the 

 fungus Ceratostomella sp. is most common, while a brown stain, of 

 which the causal fungus is probably Alternaria sp. 2 is sometimes 

 found. Staining is practically confined to the sapwood, rarely pene- 

 trating the heartwoocl. The "extent of the stain in a tree is easily 

 misjudged. As previously pointed out, there is a very dry outside 

 layer of sapwood, too dry to stain, and a hasty examination may show 

 bright wood, but deeper chopping will reveal the stain. By the end 

 of the first season all the sapwood with the exception of the outer 

 layer was heavily stained in the trees examined. In the upper por- 

 tions of the trees, where the bark had been left on, this outer layer, 

 since it had been kept moist, was also stained. The discoloration 



a Hubert, Ernest E. Some wood stains and their causes, 

 no. 11, p. 17-19, illus. 1922. 



In Hardwood Rec, v. 52, 



