[Vor. 4 
148 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
In all of these charts (1-1x), except chart 1v, showing the 
relation of specific gravity to decay, each point represents an 
average for a column of culture blocks in the original samples. 
It was necessary to take these averages in cases where one of 
the factors concerned was a property of the whole column of 
blocks, such as resin content, percentage of summer wood, 
number of rings per inch, ete. In chart гу each point герге- 
sents an individual culture block. 
Resin as an index of durability —Chart т shows the relation 
of the resin content of the wood to its decay. The percentages 
of resin are given on the primary ordinate and the percent- 
ages of loss in weight in one year on the primary abscissa. 
This chart shows two definite facts: (1) Sap-wood decays in 
all three species irrespective of resin content. The maximum 
resin content for sap-wood, however, was but 12.9 per cent 
with a loss in weight of about 13 per cent. (2) In the heart- 
wood the resin content has no definite relation to resistance in 
any one of the three species of pine. If there is any relation to 
be recognized, however, it is apparent above 12 per cent resin, 
and even here both shortleaf and longleaf pine are reduced in 
weight 12.5 per cent. Even though the reduction in the upper 
part of the chart (above 18 per cent resin) may be due en- 
tirely to sterilization, the curve below that would be very 
steep, in fact, practically parallel to the ordinate. 
Specific gravity as an index of durability.—Betts (715) has 
shown that the density of pine wood depends upon the pro- 
portion of summer wood and spring wood in the annual 
growth rings. ‘‘In tests made on a number of small pieces of 
summer wood and spring wood whittled out separately from 
wide-ring pieces of loblolly pine, the . . . density of the 
summer wood came very close to being just twice that of the 
spring wood, so that the percentage of summer wood in the 
annual rings is an indication of weight.’’ 
Chart п shows very clearly that the specific gravity of the 
samples used in this work depends upon the percentage of 
summer wood. Оп ће primary ordinate the values of specific 
gravity are represented and on the primary abscissa the per- 
