l66 R. A. STUDHALTER AND F. D. HEALD 
larger number of colonies of Endothia parasitica appeared than of all 
other fungi combined, and that all of the plates from four pieces of 
bark developed only pure cultures of the chestnut blight fungus. 
Relation to Rainfall 
With the exception of Series 5, all of the collections were made not 
more than two days after a rain. Series 5 was collected at West 
Chester on May 26. The last preceding rain, 0.56 in., fell on May 12. 
During this interval of 14 days the weather was generally fair and 
warm, offering very good opportunities for the desiccation of the 
spores. Of the nine pieces of bark tested in this series, five yielded 
viable pycnospores, ranging in number from 33 to 1181 per square 
centimeter (Table I). Assuming that the average number of p3/cno- 
spores on the day following the rain was about 75,000 per square 
centimeter, as was the case in Series 6 (Table II), the number which 
remained viable at the end of 14 days of desiccation was only a frac- 
tion of one percent of those present at the start. The significant 
fact, however, is that some pycnospores could withstand two weeks of 
desiccation in five out of nine pieces of bark tested. 
After some rains the bark remains wet or moist in sheltered places 
for several days. Some of the bark tested was still wet at the time 
of collection. This was true for all of Series 2 and part of Series i. 
On such areas of bark practically all of the pycnospores present would 
no doubt remain viable until the bark begins to dry. When the bark 
once begins to dry the number of viable pycnospores is probably 
greatly reduced by the mere act of drying, after which the further 
reduction will be more gradual. This statement is based upon the 
results obtained under certain artificial conditions (8) where the mere 
act of drying was found to reduce very greatly the number of viable 
pycnospores; once dry, the decrease was quite gradual. 
It is brought out in the last mentioned work (8) that the decrease 
in the percentage of viable pycnospores is not as great when only a 
part of the mucilaginous coating is washed off, as when all the mucilage 
has been removed. Under natural conditions in the field it is very 
probable that only a small part of the mucilage is washed away by 
rains, for it ma}^ frequently happen that fragments of spore-horns 
may remain intact with nearly all of the mucilage still surrounding 
the spores. This condition leads us to believe that the number of 
pycnospores to resist desiccation is greater on the bark below lesions 
