Ма ША ва reer ee “рам 
шая ае. г. даи чи Зала PP 
[Vor. 4 
150 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
depends on the percentage of summer wood (chart п) and 
there is a tendency toward an increase in density with a 
greater number of growth rings per inch (chart уш). These 
two facts, together with the results shown in charts ут and 
vu, indicate a more evident relation of density to durability 
than is represented by chart v. 
Summer wood as an index of durability.—Chart v1 shows 
the relation of the proportion of pine summer wood and 
spring wood to resistance to decay. Since density depends on 
the percentage of summer wood and durability seems to in- 
crease with an increase of density, it would be anticipated 
that with inereased summer wood there would be inereased 
decay resistance. Chart ут shows this to be true. А part of 
the longleaf pine containing between 45 and 55 per cent sum- 
mer wood was very resinous, and in this chart these points 
farther out should be considerably thrown back toward the 
primary ordinate to correct for sterilization. 
Chart ут shows that (1) sap-wood decays irrespective of 
species of pine and also irrespective of summer wood; 
(2) the summer wood of the heart-wood, on the other hand, 
shows a tendency to resist decay more than the spring wood, 
and is a fairly good index of durability; (3) shortleaf heart- 
wood with a high percentage of summer wood is as resistant 
to decay as longleaf heart-wood with high percentages of 
summer wood, and vice versa. 
Width of the rings of growth as an index of durability.— 
Since in specifications for structural timber the width of the 
annual rings has been closely associated with rules for grad- 
ing, which involve density, chart уп was plotted to show the 
relation of the number of annual growth rings per inch to 
decay. The number of rings per inch measured on a radius 
of the stem are represented on the primary ordinate and on 
the primary abscissa the percentage loss in weight due to 
decay. 
The results are very similar to those noted in chart ут; 
that is, we may conclude that (1) the width of the rings in 
the sap-wood of the three species of pine has little or no effect 
on the inroads of the fungus; (2) in a consideration of the 
