1917] 
ZELLER—DURABILITY OF YELLOW PINE 151 
heart-wood, the more resistant growth rings are the narrower 
ones, irrespective of species; (3) below a density of .75 the 
number of rings per inch must be closely associated with spe- 
cific gravity, that is, by correlating the results here with those 
of chart ту, there is an indication that narrower rings indi- 
cate denser, more durable wood than open wide rings. This, 
however, could not be absolute, for the wide rings are often 
more than 75 per cent summer wood. In such cases they are 
resistant to fungous attack. 
Chart уш shows the relation of the number of growth 
rings per inch to density. With the exception of those blocks 
having a density over .75 due to high resin content the ten- 
dency in this chart is to show an increased density as the 
width of the rings decrease. 
Distance from the pith as an index of durability Chart тх 
shows that distance from the pith, or age of the heart-wood, 
is no index of the durability of the heart-wood. Tests were 
made on pieces up to 16 inches in diameter. The sap-wood 
decays irrespective of distance from the pith. 
SERIES B 
See description of series В and table п above. 
SERIES C 
Chart x shows the relation of resin to the decay, induced by 
L. saepiaria, of yellow poplar blocks impregnated with resin. 
On the primary ordinate are represented the percentages 
of resin and on the primary abscissa the percentage loss 
in weight in one year. The plotted points are well scattered 
and show no definite course, unless there is a tendency to in- 
crease in percentage of decay with an increase of resin. When 
this is compared with chart x1, which shows the same rela- 
tion for Polystictus hirsutus, there is an interesting contrast, 
for Polystictus seems to be inhibited, if anything, by resin. 
Although the points are well scattered, there is a tendency to 
show that Lenzites thrives more or less on benzol-soluble sub- 
stances when infiltrated into the wood, while Polystictus, 
which usually grows on hard woods, does not. 
