510 Journal of Agricultural Research Vol. IIL, No. 6 
Tani IX.—Percentage of the number of spores of Endothia parasitica to the total spore 
content of the air, as shown by exposure-plate tests on chestnut-bark agar in 1913 at West 
Chester, Pa. 
Per- Per- 
Lento: Num. |of colo: 
- = | Ol colo- 
Total | Bort | ‘nies of Total | ber of | nies of 
num | colo- | Endo- erat | colo-_ | Endo- 
Plate ber of | nies of | thia Plate Date, fun, | ties of | thia 
No. Date: fun- | Endo-| para- No. ~ | Endo- | para- 
Boo. | thia | sitica , ae, (| _thia sitiee , 
‘i - | to tot : para- 
nies. | Utica. snore mIES. | Sitica, sore 
content content 
of air. of air. 
4383 | Aug. 27.....| 30 16 53 || 5046 | Sept. 20....) 9 7 7 
4384 |...do....... 25 21 84 5047 |...do....... It Io gr 
4385 |...do....... 70 33 47 || 5048°|...do....... 6 6 100 
4386 |...do....... 25 20 80 || 5049 |...do....... 9 7 77 
4787 | Sept. 18....] 20 II 55 || 5050 |...do....... 6 3 50 
go4r | Sept. 20....] z2 10 83 5069 | Sept. 21....| 30 12 49 
5042 |...do....... 9° 7 47 || so7o |...do....... 50 20 40 
5043 |...do.......] 10 4 40 || 5071 |...do....... 70 62 88 
5044 |...do....... 23 22 O5 | §072 |xc.dOswaces 28 24 85 
5045 |...do....... 14 Iz 48 || 5073 |...do....... 2I 19 go 
In connection with these figures it should be borne in mind that the 
fungi represented are such as will grow only on chestnut-bark agar. 
Taking into consideration, however, the relatively large numbers of other 
fungi ordinarily developing in the exposure plates (Table I), it is a note- 
worthy fact that at certain periods when ascospore expulsion was in 
progress the spores of this one species should constitute from 40 to 100 
per cent of the total spore content of the air. 
Since these plates were exposed not long after a rain, a possible expla- 
nation suggested is that spores of other fungi were washed from the air 
by the rain and the supply had not yet been replenished, whereas condi- 
tions were very favorable to the abundant expulsion of ascospores of 
Endothia parasitica. It has also been suspected that certain types other 
than this fungus which were often found in plates exposed at such times 
represented other ascomycetous fungi the spores of which had just been 
expelled. 
SUMMARY OF EXPOSURE-PLATE TESTS 
In all of the exposure plates yielding colonies of Endothia parasitica it 
was determined from the time of appearance of these colonies that all 
originated from ascospores. Therefore we may safely state at the outset 
that under the conditions of the tests little or no wind dissemination of 
pycnospores occurred. 
By comparison with ascospore-trap tests it is evident that ascospores 
of Endothia parasitica were caught in the exposure plates in numbers and 
at some distances from trees only during certain periods following rains 
when ascospore expulsion was in progress. The possible exception 
occurred on the morning of September 8, when no series of observations 
was made on the ascopore traps. ace 
As the occurrence of ascospores in the air in considerable numbers is 
the prime requisite for wind dissemination and as ascospore expulsion 
