Mar. 25. I9IS Dissemination of Chestnut-Blight Fungus 519 



The aspirator tests do not appear to have given as reliable results as 

 the exposure-plate method, since it may be noted from Table XV that 

 negative results were obtained on certain days when the exposure plates 

 showed that ascospores were prevalent. The importance, however, of 

 the aspirator tests lies in the fact that ascospores were obtained under 

 perfectly natural conditions in the field at a distance of 13 feet from the 

 nearest lesion and that they were obtained at times when ascospore 

 expulsion was taking place. 



WATER SPORE-TRAP TESTS 



The use of water spore traps for testing the transport of spores of the 

 chestnut-blight fungus by the wind was the outcome of our attempts to 

 use the method of Burrill and Barrett (3) in their study of the wind 

 dissemination of Diplodia zeae. First, substituting a funnel for the glass 

 plates employed by the writers just cited, an attempt was made to find 

 some mixture which could be applied to the inner surface of the funnel 

 and which would fulfill the necessary requirements, as follows: 



1. The mixture must contain no substances toxic to spores of the 

 chestnut-blight fungus. 



2. It must spread readily and adhere to a glass surface. 



3. It must be sticky, so as to retain the spores which lodge upon the 

 surface, which is coated with it. 



4. It must retain its sticky character at least 24 hours under field con- 

 ditions. 



5. It must be readily soluble in water. 



Glycerin of various percentages was tried alone, as well as in combina- 

 tion with various quantities of gum arable or gelatin, but in all cases the 

 mixtures either dried too soon or did not spread well on a glass surface. 



The fact that pycnospores do not germinate in water (4) suggested the 

 substitution of dishes of sterile water for the funnels. The first idea was 

 that analyses of the water from these dishes exposed in the field under 

 natural conditions could be made at intervals of some days and would 

 reveal the presence of pycnospores if they had been carried by the wind. 

 Experience in the field, however, proved that the method was also well 

 adapted to the study of ascospore dissemination. 



DESCRIPTION OF THE WATER SPORE TRAPS 



A water spore trap consisted of a crystallizing dish 5 cm. deep and 10 to 

 12 cm. in diameter, into which sterile water was introduced. The dishes 

 were wrapped in paper and sterilized in the laboratory for transport to 

 the field. Each dish was supported about 2 feet above the ground by a 

 tripod of three small stakes driven into the ground. Ten-penny nails 

 were driven into the ends of the stakes, whose ends were converged to 

 make a support for the dish. The nails were held in proper position 

 by a heavy cord attached to them and encircling the dish. By this 

 means they were so firmly secured that they were never in danger of 

 being blown out by the wind (PI. LXIV, fig. 3). After placing a dish in 

 its proper field location, 100 to 150 c. c. of sterile water were introduced. 

 Water for this purpose was kept in stock in small Ivrlenmeyer llasks. 



The dishes of water were exposed in the field in various selected loca- 

 tions and analyses made at certain intervals (fig. 3; also PI. LXV, figs. 

 I and 2). 



