16 
BULLETIN 510, U. S. DEPARTMENT OF AGRICULTURE. 
1 to 2 feet (fig. 16) or set on short posts. A few of the best mills 
make use of concrete piers for this purpose. The latter type of 
foundation would be greatly improved by the use of stringers treated 
with a wood preservative. 
The dangers arising from partially rotted foundations are evident, 
as has been seen from the earlier discussion of the activities of wood- 
destroying fungi. Where wood blocks are used to support the skids, 
fungi often progress directly from the moist soil upward, in this way 
frequently infecting the skids, thus adding the possibility of direct 
mycelial infection to 
that of spore infec- 
tion. The infected 
skids themselves are 
dangerous, since the 
fungous mycelium 
can progress directly 
from them to the bot- 
tom of the lumber 
piles (PL IV, fig. 3; 
text fig. IT). Once 
started, , and the 
weather conditions 
being warm and 
moist, such infections 
may pass through an 
entire stack. In con- 
sidering the menace 
of infected skids, we 
must also not lose 
sight of the fact that 
such timbers are a 
prolific source of 
fruit bodies (PI. Ill, 
fig. 3) with their 
many spores, to be 
borne up into the 
lumber piles either directly by the wind or by convection currents 
which occur in relatively still air. The proof of this latter form of 
air currents is often before us in the form of rising mists or fogs. 
The first requisite in building foundations is to get them well off 
the ground, so as to allow ample ventilation beneath, which will 
dry out the timbers themselves as well as the soil below. A height 
of at least 24 inches from the top of the skids to the surface of the 
ground should be adhered to. 
P77F 
Fig. 12. — Rotten base of an old hardwood stack upon 
which sound lumber has been piled. This is a most 
insanitary practice, as fungous infection will be spread 
both by the contact of the diseased with the sound lumber 
and indirectly by the production of fruit bodies and 
spores, the latter blowing about, reaching sound mate- 
rial, and germinating to produce new infections. 
