5i8 



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. 



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 Endoihia parasitica 

 obtained may be due to the effect of sunlight, for in those instances where 

 tlie 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 1013 at West Chester, Pa. 



Date of rain. 



Aug. 27. . . 

 29-30 



Sept. 7-8 . . 

 12-13 

 17-18 

 18-19 

 19-20 

 20-21 

 21 . . . 

 21-22 



Rainfall. 



Date of aspiration. 



Iiuhes. 



0-175 

 10 



37 



09s 



26 



68 



09 



43 

 10 



73 



Aug. 27 



30 

 Sept. 7-1 



13 

 18 



19 

 20 

 21 

 21 

 22 



Quantity of 

 air tested. 



Liters. 



12 

 60 



12 



68 



52 

 96 

 76 

 40 

 28 

 52 



Number of 

 spores of 

 Endotliia 

 parasitica 

 to 10 liters 

 of air. 



4.2 

 O 



o 

 o 



I. 92 

 o 

 o 



l'2S 



Results with 

 exposure 



plates. 



+ 



+ 

 + 

 + 

 + 

 + 

 + 



The chief explanation of the small number of spores of Endotliia para- 

 sitica 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 the}' 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 

 have been stray spores similar to those obtained in several exposure 

 plates. 



