1917] 
ZELLER—DURABILITY OF YELLOW PINE 149 
centages of summer wood. As the percentage of summer 
wood increases the specific gravity increases. 
Chart nr shows the relation between specific gravity and 
the percentage of resin. The values of the specific gravity 
are given on the primary ordinate and the percentages of 
resin on the primary abscissa. Above a specific gravity of 
.75 the resin content may influence the weight considerably, 
but below this weight there seems to be no definite relation 
in any of the species, the longleaf and shortleaf pine being 
mixed quite evenly. 
Chart 1v shows the relation of specific gravity to dura- 
bility. On the primary abscissa are represented the per- 
centages of loss in weight in one year and on the primary 
ordinate the values of the specific weights. As was men- 
tioned above, in this case below .75 specific gravity, there 
is a high percentage of failures in inoculation, and conse- 
quently a congestion of plotted points along the primary 
ordinate in this region. Above .75 specific gravity the 
curve gradually swings away from the primary ordinate 
due to the loss of weight in sterilization. Thus, before 
considering the meaning of this chart it will be necessary 
to consider this upper portion of the chart with the points 
moved back toward the primary ordinate. 
This chart was plotted on the basis of individual culture 
blocks, and shows that (1) sap-wood decays irrespective of 
density or species; (2) there is a perceptible curve showing 
that irrespective of species the lighter heart-wood decays 
more readily than the more dense heart-wood; (3) loblolly 
pine, however, is generally lighter than longleaf and shortleaf 
pine, the two latter being fairly evenly distributed. 
Chart v shows the same relation as illustrated in chart ту, 
but differs from the latter in that the plotted points represent 
averages for columns of culture blocks rather than the indi- 
vidual blocks. The general points brought out by this chart 
are the same as in chart ту, except that the curve for heart- 
wood becomes more abrupt and the apparent increase of dura- 
bility due to an increase of density becomes less evident here 
than in chart ту. However, the specific gravity of pine wood 
