518 Journal of Agricultural Research Vol. III, No. 6 
DISCUSSION OF RESULTS OF ASPIRATOR TESTS 
The results obtained from these tests are presented in Table XIV. 
The average number of bacteria per liter of air was 2.91, while the number 
of fungi per liter averaged 7.03. The number of fungus species repre- 
sented in the cultures ranged from 3 to 14. ; ne 
In only five instances did any colonies of the chestnut-blight fungus 
appear in culture, and the number of spores per liter was never large. It 
is not impossible that the small numbers of spores of Endothia parasitica 
obtained may be due to the effect of sunlight, for in those instances where 
the rains were followed by fair weather the aspirator was exposed to the 
direct rays of the sun for a part of the day. This may also be the expla- 
nation of the fact that no spores of E. parasitica were obtained after some 
of the rains when ascospore-trap collections made it certain that expulsion 
was taking place, notably those of September 7 and 8 and September 21 
and 22 (Table XV). Unfortunately there are no published investigations 
which give any information on the effect of sunlight on ascospores of the 
chestnut-blight fungus. 
TaBLE XV.—Relation of aspiration tests to rainfall in 1913 at West Chester, Pa. 
Number ‘ 
; clothes | Results with 
Date of rain. Rainfall, Date of aspiration. Suan i aie exposure 
to ro liters plates. 
of air. 
Inches. ’ Liters. 
Aug. 27.... 0.175 | Aug. 27.......... 12 4-2 + 
29-30.. 1.10 Oeees crane 60 ° — 
Sept. 7-8... -37 | Sept. 7-8......... 12 ° + 
12-13 - 095 EG ores davavercat ie 68 ° - 
T7-18. 2.0... 26 IS. siete 52 I. 92 + 
18-19 - 68 AQ ich dnead 96 ° + 
19-20 +09 20! bccn: 76 ° + 
20-21 - 43 BE re someicsceran 40 I. 25 + 
21 Io 20 ae viegass 28 89 + 
21-22 73 ere 52 ° + 
The chief explanation of the small number of spores of Endothia para- 
sttica to the liter is to be found in the small amount of air drawn through 
each tube. While this averaged 38 liters for those tubes yielding positive 
results, only a few liters were drawn through the tube in the several hours 
during which copious expulsion of ascospores took place. The figures 
given in the tables are therefore smaller than the actual number of 
spores per liter during the period of copious expulsion. In view of 
these facts, Tables XIV and XV do not represent the true number of 
ascospores present in the air during the time of their actual prevalence, 
since the period of aspiration included many hours when they were not 
prevalent, as shown by the exposure-plate tests. 
The rate of development of the colonies of the chestnut-blight fungus 
showed that they all originated from ascospores and none from pycno- 
spores (5). 
The spores obtained from sugar tube No. 7 two days after a rain may 
feeb been stray spores similar to those obtained in several exposure 
plates. 
