Mar. 2s. 1915 Dissemination of Chestnut-Blight Fungus 



523 



following the rain. This appears to be substantiated by negative re- 

 sults obtained during dry periods and by positive results obtained with 

 exposure plates and slide traps just following a period of rain. The 

 results are briefly summarized in Table XIX. It is interesting to note 

 the number of viable ascospores of the chestnut-blight fungus that must 

 have fallen on each square inch of water surface for the time represented. 

 This information is presented in Table XX. 



Table XIX. 



-Summary 0/ positive results obtained from water spore traps in igij at 

 West Chester, Pa. 



Table XX. — Number of ascospores of Endothia parasitica falling on each square inch of 

 water surface at various distances in igij at West Chester, Pa. 



The large number of spores of Endothia parasitica falling on each 

 square inch of surface for a single rainy period certainly emphasizes the 

 fact that healthy trees in the vicinity of badly diseased ones have innu- 

 merable opportunities to become infected by wind-borne spores. 



It should be mentioned in this discussion of the results obtained by 

 the water spore traps that there are some possibilities of error. It might 

 be claimed that the spores found in the water traps were carried by 

 birds or insects. This, however, appears exceedingly improbable. The 

 cultures alwavs indicated ascospores and tests have shown that birds are 

 carriers of pycnosporcs only (8). The position of the traps was such as 

 to reduce the insect visitors to a minimum. Insects tested as carriers 

 of the chestnut-blight fungus yielded both pycnosporcs and ascospores, 

 but the former were very much more abundant (17). Besides, it was 

 rare that any insects were found in the exposure dishes. Furthermore, 

 spores were present in the traps only at periods following rains when 

 other tests had indicated their prevalence. 



