Annals 
of the 
Missouri Botanical Garden 
Vor. 5 APRIL, 1918 No. 2 
CORRELATION OF THE STRENGTH AND 
DURABILITY OF SOUTHERN 
PINE 
SANFORD M. ZELLER 
Visiting Fellow in the Henry Shaw School of Botany of Washington University 
INTRODUCTION 
It has been known for some time that the strength of 
pine structural timbers is a function of specific gravity 
(density). About twenty-five years ago Johnson! demon- 
strated by actual tests on longleaf pine (Pinus palustris) that 
there is a regular increase in average strength with an in- 
crease in density, and this is especially true where all of the 
pieces tested are reduced to a standard dryness. He also 
pointed out that compression endwise tests parallel with the 
grain give the best indication of the general strength value of 
the wood. 
Since these earlier studies many testing laboratories have 
continued to establish relations between the physical and 
mechanical properties of wood. This is especially true of the 
Forest Products Laboratory maintained by the United States 
Forest Service and the Purdue University Laboratory for 
Testing Materials. The results of the tests made by the 
Forest Service and others were discussed by Betts? before the 
American Society for Testing Materials, and rules for grad- 
2 Johnson, J. В. Timber physics. Investigations on longleaf pine. 4. Results 
on mechanical tests. U. S. Dept. Agr., For. Div. Bul. 8: 22-31. f. 11-16. 1893. 
Discussion of the proposed Forest Service rules for grading the 
strength of southern pine structural timbers. Proc. Am. Soc, for Testing Materials 
151: 369—384. f. 1-9. 1915. 
ANN. Mo. Вот. GARD., VOL. 5, 1918 (109) 
