1. Each successive ridge shows a decrease in the number of old
infections, from the Blue Ridge northward.
2. There is more blight along the south slopes than on the adjacent
north slopes.
3. Recently cut stumps with their sprouts show a high per cent. of
infection even where adjacent tracts are clear of blight.
4. Centers of infection are found under all conditions. Slope,
exposure, drainage, rock formation, and fertility of the soil seem to
have no relation to origin of infections.
5. A large number of infections one and two years old began in wounds
made by cicadas in 1911.
6. Wind appears to be the most important factor in the dissemination of
the blight. Birds may be factors as carriers of the original infecting
spores, but cannot be blamed for the local distribution of the blight
around an infection center. This distribution is very uniform, which
presumably would not be the case had birds been the principal carriers
of the disease. In young coppice growth much wounded by cicadas, the
wounds on the twigs are the chief points of entrance for the disease.
Results of accurate counting show that on certain tracts 80 to 90
per cent. of new infections began in such wounds made by the 17-year
cicadas during their invasion of 1911. Many new infections are at and
near the bases of young sprouts, and there is little cause to believe
that these were due to birds, since they are usually about the same
age and at points that birds are not likely to frequent. Also, this
condition exists on exposed north slopes little visited by birds. The
most plausible explanation seems to lie in the hypothesis of wind
dissemination. This explains the numerous infections starting in cicada
stings; also the rapid spread over a tract of young sprouts; the common
occurrence of new infections on trees standing alone, in exposed
places. The greater quantity of infection on south slopes appears to be
due to the fact that the prevailing winds are southerly and easterly
during the periods when ascospores are extruded in greatest numbers.