ГУ от. 4 
96 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
Mayr distinguishes between the liquid resin, as it is found 
in the sap-wood of conifers, and solid resin, such as fossil 
amber. Fungi such as Nectria and Pestalozzia thrive on the 
soft resin, while the hard resin is very durable. Thus, the 
greater the amount of hard resin wood contains, the more 
durable will it be. He suggests that the influence of resin 
should not be overestimated, however, since other factors, 
such as density or specific gravity, dark color due to the im- 
pregnation with ‘‘Dauerstoff,’’ climatic conditions under 
which the trees were grown, and the duration of seasoning, 
are of much greater importance in decay resistance. On the 
other hand, where different species of coniferous wood have 
the same specific gravity, Mayr ascribes the differences in 
durability to variations in resin content. Pieces of spruce, 
larch, and Douglas fir, for instance, often show the same spe- 
cific gravity, but the spruce and larch are generally more 
durable than the Douglas fir, since the latter is considerably 
inferior in resin content. 
Mayr further says that for the judging of the durability of 
all species of wood, the **Dauerstoff," a substance ог sub- 
stances which cause the dark color of heart-wood, must be 
taken into consideration; that is, that a species of wood pos- 
sessing dark heart-wood surpasses in durability that with 
light-colored heart, providing the resin content and specific 
weights are the same. 
The climatic conditions under which the trees are grown 
will influence the durability of the wood. Mayr suggests the 
pine as an example of this fact. For instance, the timber 
grown in relatively warm climates on sandy soils possesses 
a dark, broad heart, while that produced on gravelly soils in 
cooler climates has narrow, light-colored heart-wood, and un- 
der warmer conditions the wood is specifically heavier and 
possesses a greater resin content than in cooler regions. 
It is also suggested in Mayr’s conclusions that the season- 
ing of the wood influences the durability because of its effect 
on the resin content. If seasoning is rapid the resins may be 
carried out of the wood by the evaporation of the turpentine 
