Forest Service, U. S. Dept. of Agriculture Mechanical Pulp. 



PLATE II. 





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FIG. 1. NATURAL SURFACE OF STONE. (JACK PINE RUN No. 2.) 



FIG. 2. TEN TO THE INCH SOLID; STRAIGHT-CUT BURR. (HEMLOCK RUN No. 0.) 



FIG. 3. EIGHT TO THE INCH SOLID; SPIRAL BURR. (HEMLOCK RUN No. 43.) 



