5IO 



Journal of Agricultural Research 



Vol. m. No. 6 



Table IX. — Percentage of the tiumber of spores of Endothia parasitica to the total spore 

 content of the air, as shown by exposure-plate tests on chestnut-bark agar in igi3 at West 

 Chester, Pa. 



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. 



As the occurrence of ascospores in the air in considerable numbers is 

 the prime requisite for wind dissemination and as ascospore expulsion 



