496 Journal of Agricultural Research voi. m. No. 6 



The author admitted, however, that the observations reported were 

 rather meager in support of this conclusion. 



PURPOSE AND SCOPE OF PRESENT WORK 



Since most of the previous work on wind dissemination of the chest- 

 nut-blight fungus which yielded positive results was done under artificial 

 conditions, it was the aim of the present writers to studj' the problem 

 under absolutely natural conditions. Briefly stated, the purpose of these 

 tests was to determine whether or not, and if so, to what extent, wind ' 

 acts as an agent in dissemination of the spores of this fungus. It was 

 also the object of the work herein recorded to ascertain at what particu- 

 lar times under natural conditions spores of Endothia parasitica are preva- 

 lent in the air, the possible distances transported by the wind, and the 

 kind of spores (whether ascospores or pycnospores). 



The locality chosen in which to conduct our tests was a 4-acre plot of 

 native chestnut {Castanea dcntata) coppice near West Chester, Pa. The 

 trees in this plot ranged from 4 to 8 inches in diameter and all were badly 

 infected with the chestnut blight, many having already succumbed. 



In these tests, which covered a period of 36 consecutive days during 

 August and September, 191 3, four methods were employed in studying 

 the points in question. To determine the prevalence of spores of En- 

 dothia parasitica in the air at particular times and places a series of 756 

 exposure plates was made. The occurrence of ascospore expulsion was 

 detected and its exact period of duration ascertained by the examina- 

 tion of ascospore traps in the shape of object slides supported over peri- 

 thecial pustules on the trees. The number of spores present in the air 

 was determined quantitatn^ely by the aspirator method. Rather pro- 

 longed exposures of water spore traps, consisting of sterile water in dishes, 

 were made to secure additional information as to the kind of spores in the 

 air, the periods of occurrence, and the distance transported. 



EXPOSURE-PLATE TESTS 



In testing the spore content of the air among diseased trees in the 

 field for the presence of spores of Eiidolhia parasitica the exposure of 

 sterile poured plates of chestnut-bark agar proved to be the most satis- 

 factory method. The use of chestnut-bark agar ^ was found advan- 

 tageous, since this medium inhibits the development of bacterial colo- 

 nies and retards the growth of rapid-growing fungi, spores of which are 



' Falck has pointed out the importance of convection currents in the dissemination of ascospores. (Falck, 

 Richard. Uber die Luftinfektion dcs Muttcrkomcs (Claviceps purpurea Tul. ) und die Verbrcitimg 

 pflanzlicher Infektionskrankheiten durch Temperaturstrumungen. /n Ztschr. Forst- u. Jagdw., Jahrg. 

 43. No. 3. p. 202-227. 4 fig., 1911.) For this reason we have used the word "air" in the title of the present 

 paper. 



2 Chestnut-bark agar was made according to the following formula: Add 50 gm. of finely chopped or 

 ground air-dry chestnut bark to j.ooo c. c. of distilled water and boil for 15 minutes. Filter through 

 cheesecloth or absorbent cotton and add water to make up to 1,000 c. c. Add 15 gm. of agar and boil until 

 the agar has melted; then cool to 60° C. or under, clear with the whites of two eggs, filter, and sterilize in 

 the autoclave. 



