1917] 
ZELLER—DURABILITY OF YELLOW PINE 153 
by an examination of the percentage of summer wood. The 
more desirable pieces of timber are those containing broad 
bands of summer wood and narrow bands of spring wood as 
shown in the cross-section. 
(9) The investigations thus far have been conducted to 
ascertain the toxic effect of resin on the fungous decay of 
wood. The results have shown that there are no toxic effects, 
but that there are other important relations of resin to decay, 
as, for instance, its waterproofing effect on wood and, thus, 
its influence on the absorption of moisture by wood contain- 
ing it; that is, the power of wood to absorb moisture is very 
important in its decay. It is well known that below a certain 
minimum and above a certain maximum of moisture in wood 
Leneites saepiaria and other similar fungi will not grow. Any 
property of the wood which will influence this balance of 
moisture is of importance in decay resistance. Thus, if the 
wood eontains enough resin to have a material waterproofing 
effect it must play a róle in durability. However, at present 
the percentage of resin necessary for such an influence is un- 
known. From the analyses given above it may be assumed 
that it is at least 5 per cent or more, but this would not be a 
safe basis for specifying decay resistance, since a piece of 
timber of low summer wood percentage (density) may contain 
this amount of resin, and yet be porous enough to be attacked 
by fungi. On the other hand, although not an absolute rule, 
it is generally true that a dense piece of heart-wood showing 
dark summer wood is more liable to contain at least 5 per 
cent resin than is a lighter piece. Hence, specifieations based 
on high percentage of summer wood in most cases would more 
nearly fulfil requirements for durability than those based on 
resin content, at least until more is known concerning the in- 
fluence of resin on the moisture-absorbing power of wood. The 
relation of resin to the absorbing power of pine timbers and 
the optimum relative humidity of the air for the decay of 
resin-containing wood are problems for further investiga- 
tions. When this work is taken up again due consideration 
will be given to correcting the error due to sterilization. At 
a later time the probable error of the mean when dealing with 
