540 ANNUAL REPORTS OF DEPARTMENT OP AGRICULTURE. 



During the year a study was made of the pith-ray flecks, or medul- 

 lary spots, which occur in many native woods. These are caused by 

 the larva3 of an insect which live in the cambium during the growing 

 season, and discolor the wood, often rendering it unfit for certain 

 uses. The study dealt with the kinds of trees affected, the means by 

 which the larva? obtain entrance to the cambium, the geographical 

 distribution of the insect and the factors affecting the local distribu- 

 tion of larva} and mines, and the deteriorative effect on the wood. 



Hand collections of the chief commercial woods of North America 

 were prepared for the use of schools and of branches of the F'orest 

 Service needing such material. In cooperation with the Bureau of 

 Plant Industry, 100 important Panama woods were described and 

 illustrated for a proposed publication dealing with the trees and 

 woods of the Isthmus. A catalogue of national forest flora was 

 prepared, showing on which national forests certain species occur. 

 The study of the effect of shade on hardiness of coniferous seed- 

 lings, begun in 1911, was continued. As in former years, a number 

 of wood samples submitted by manufacturers and other wood users 

 were identified. 



STUDIES OF FOREST PRODUCTS. 



Work in forest products during 1912 was of broader scope, greater 

 volume, and productive of more important results than in any pre- 

 vious year. 



STRENGTH TESTS. 



The work of testing woods grown in the United States as a means 

 of assisting users to select the species best adapted to a given pur- 

 pose or to find substitutes for species becoming difficult to obtain 

 was actively carried forward. During the year 23,882 tests were 

 made on 35 species of wood. By the systematization of this work 

 the cost of making tests has been steadily reduced, until now it 

 amounts for each test to approximatelj'^ 50 cents, or about half the 

 cost prior to the establishment of the Forest Products Laboratory. 

 The tests will be continued until all species of commercial impor- 

 tance growing in the United States have been covered. 



The work in connection with structural timbers was confined dur- 

 ing the year mainly to analyses of test data previously obtained for 

 longleaf, shortleaf, and loblolly pine, Douglas fir, western hemlock, 

 western larch, Norway pine, tamarack, and red spruce. One impor- 

 tant result was to show that many of the defects which have been 

 the basis of culling timbers do not seriously affect their value for 

 structural purposes. Another fact brought out is that western hem- 

 lock, generally considered an inferior timber, is entitled to a place 

 among the important western woods. Green western hemlock 

 stringers showed an average strength 88 per cent as great as that of 

 Douglas fir, one of the chief construction timbers of the United 

 States. Western larch, another little-used wood, showed a strength 

 81.7 per cent of that of Douglas fir. Besides determining the rela- 

 tive mechanical properties of the different woods, the results of these 

 tests permit the formulation of grading rules that classify timbers 

 according to strength. Tests were started on western yellow-pine 

 car sills and floor beams and were completed on that portion of the 



