Mar. 35, 191S Disse initiation of Chestnut-Blight Fungus 



503 



Table III. — Record of exposure plates made on August 27, /p/j, at West Chester, 



Pa. — Continued 



RAIN NO. 2 Co.os.'i INCH. 5.35 TO 5.50 P. M.) 



The second shower on August 27 took place late in the afternoon, and 

 though the precipitation was Hght, the cumulative effect of this rain upon 

 that of the preceding one caused abundant expulsion of ascospores. The 

 four plates exposed within about half an hour after this shower yielded 

 colonies of E. parasitica in such numbers as to prove bejond doubt that 

 the ascospores were at that time very prevalent in the air. The ascospore- 

 trap tests for this period (Tables X and XVII) showed that, although out 

 of the 14 examined only i bore any evidence of spore expulsion during 

 the first 15 minutes after the cessation of the rain, 12 out of 14 showed 

 expulsion of ascospores during the time in which the plate exposures were 

 made. The sun had gone down, and the weather conditions following 

 this storm were not conducive to the rapid drying of the bark. The results 

 of this date were the first evidence secured which indicated beyond 

 doubt that ascospores of Endothia parasitica are disseminated by wind 

 under natural conditions. 



During the dry, hot weather of August 28 evidently no sporesof Endothia 

 parasitica were present in the air, nor were any detected on August 29. On 

 this date the humidity was high and cloudiness prevailed, accompanied 

 by traces of rain insufficient to cause ascospore expulsion. As there was 

 a rainfall of i.io inches in the evening of August 29, several plates were 

 exposed in rapid succession the next morning, but no spores were caught. 

 This failure is attributed to the fact that once more too long a time had 

 passed since the rain ceased, and spore expulsion, though probably abun- 

 dant in the night, had no doubt ceased long before the first exposures were 

 made. Throughout the following week there was no rain, and no ascopore 

 expulsion occurred at any time. 



For the night previous to September 8 a rainfall of 0.37 inch was 

 recorded, the time of cessation being prior to 1.30 a. m. The ascopore 

 traps gave evidence of plentiful spore expulsion. Between 6.27 and 8 

 a. m. eight exposures were made before the sun had dried the vegetation 

 and while the bark was still wet in places. Three of these plates yielded 

 colonies of Endothia parasitica, and as two of them were exposed at sta- 

 tions more or less in the open, it would seem that ascospores were at that 

 time prevalent in the air to some extent. The third plate and also five 

 others exposed at later intervals during the day each yielded one colony 

 of E. parasitica. 



Of the plates exposed on September 9, a dry, hot day, two in the morn- 

 ing also yielded one colony each of Endothia parasitica. During the dry 

 weather of ,Septembcr 10 and 1 1 negative restiUs were obtained. 



