[Vor. 4 
152 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
CONCLUSIONS 
It would seem that, from the results of the preliminary 
experiments discussed above, it would be safe to conclude 
hat: 
(1) Resin is no safe index of the durability of the three 
species of yellow pine investigated. Resin is not only unde- 
sirable for specifying durability because it is no safe index 
of decay resistance, but also because of the expenditure of 
time and labor necessary to make resin percentage deter- 
minations. 
(2) On the other hand, specific gravity or density of the 
wood materially influences resistance to decay of the heart- 
wood, i. e., the more dense the wood the more durable it is, 
irrespective of the three species of wood examined. 
(3) Specific gravity, however, is a property which can not 
be determined from inspection, but it can be estimated by 
recourse to the proportion of summer wood to spring wood 
in the growth rings, which proves to be a safe criterion of the 
durability of heart-wood; i. e., an increase in summer wood 
results in an increase in specific gravity. 
(4) The width of the growth rings furnishes a further in- 
dex of durability, the narrower rings showing more resistance 
to fungous attack than broad, open rings. 
(5) The age, or distance from the pith of heart-wood, shows 
no relation to durability, at least up to 16 inches in diameter. 
(6) Sap-wood decays irrespective of resin content, specific 
gravity, width of the annual rings, or species of pine. 
(7) Shortleaf heart-wood or loblolly heart-wood is as dura- 
ble as longleaf heart-wood, provided it has the same qualities 
as to specific gravity or density. 
(8) Specifications for durability of the three species of pine 
considered should be based on a judicious combination of spe- 
cific gravity, number of rings per inch, and the percentage of 
sap-wood. In other words, where pieces of the highest lasting 
powers are desired it will be necessary to specify pieces of the 
greatest density and with a minimum percentage of sap-wood. 
For inspection purposes the specific gravity may be estimated 
