524 Journal of Agricultural Research voi. iii.no. e 



CONCLUSIONS 



(i) As a result of 756 exposure plates made in or near the badly 

 diseased chestnut coppice at West Chester, Pa., it can be definitely 

 stated that ascospores of Endothia parasitica (Murr.) And. are prevalent 

 in the air and after expidsion are carried for varying distances from their 

 source. 



(2) As shown by the same exposure plates, the period of prevalence 

 of ascospores varies with the conditions following the cessation of rains; 

 when there is a rapid drying of the bark, this period is short, but when 

 drying is retarded, this period is correspondingly extended. The tests 

 indicate a general prevalence of ascospores within the first 5 hours fol- 

 lowing the cessation of rains, with less abundance during later hours. 

 The longest period for our entire series was 14 hours. 



(3) During periods of dry weather ascospores, although not generally 

 prevalent, may occasionally be detected by the exposure-plate method. 

 These are apparently stray ascospores expelled during some previous 

 period of rain and now loosened from lodgment on some near-by objects. 



(4) In and near badly diseased chestnut groves or forests the number 

 of ascospores falling on each square foot of exposed surface following a 

 period of rain, as indicated by exposure plates, is very large and is suffi- 

 cient to offer abundant opportunity for new infections. 



(5) Ascospores are forcibly expelled in large numbers from the peri- 

 thecia during and after each warm rain in case the amount is sufficient 

 to soak up the pustules. Following a dry period a rain of 0.18 to 0.25- 

 inch has been observed to cause copious expulsion of ascospores, while 

 rains of o.oi to o.io inch, if immediately preceded by a copious rainfall, 

 have been sufficient to cause the resumption of spore expulsion. 



(6) As determined by the ascospore traps, the duration of expulsion 

 depends on the rapidity with which the bark dries and only continues 

 when the stromata are moist. Under natural conditions in the field 

 the period of expulsion for eight rains varied from 45 minutes to 13 

 hours and 14 minutes. 



(7) In some cases at least the maximum of ascospore expulsion occurs 

 after the cessation of rain. 



(8) The fact that the period of ascospore expulsion as determined by 

 the ascospore traps coincides in general with the period during which 

 spores were obtained by exposure plates points to these forcibly expelled 

 spores as the ones prevalent following periods of rain. This is definitely 

 substantiated by the development of colonies in the exposure plates 

 from ascospores only. 



(9) It is possible to determine the presence of ascospores of the chest- 

 nut-blight fungus in the air under natural conditions in the field by the 

 standard aspirator method of bacteriological analysis. By this method 

 positive results were obtained following four different rainy periods, but 

 only when the period of aspiration included a period of copious ascospore 

 expulsion. 



(10) By the use of water spore traps stationed at varying distances 

 from diseased trees it was possible to determine that ascospores are 

 prevalent in the air and fall upon exposed surfaces in considerable 

 numbers, the number diminishing with the distance from the source of 

 supply. 



