Pathogenicity of the Chestnut Bark Disease 49 



ascospores in from 10 to 30 minutes after they had been ,wet and 

 would continue to discharge for from one to five hours. ~The 

 distance the spores were shot varied from 5 to 25 mm. The ex- 

 pulsion of ascospores depends not only upon the presence of suffi- 

 cient moisture but also upon the temperature to which the lesion 

 has been subjected. Laboratory tests have shown that bark bear- 

 ing perithecial pustules, if subjected to low temperatures (5.5 to 

 7.8 C.) for a period of several hours, would not begin the ex- 

 pulsion of ascospores until exposed to favorable temperatures 

 for three or four days, although supplied with an abundance of 

 moisture. Minimum temperatures at which spore expulsion takes 

 place vary from 11.0 to 15.5 C. 



Dissemination. 



The study of the dissemination of the disease \vas consid- 

 ered a very important phase of the work requisite to the finding 

 of an efficacious means of control'. Every probable means of 

 dissemination was investigated. 



As explained above, rain is one of the factors which must 

 be considered in the dissemination of the fungus. It is believed 

 that the influence is even greater than to merely stimulate the ex- 

 pulsion of the ascospores from the perithecia. Specimens of bark 

 received during the early spring of 1912 bearing perithecia with 

 long necks, on being placed in a humid environment, in twelve 

 hours showed clumps of ascospores clinging to the necks of the: 

 perithecia. These were ripe when examined under the micro- 

 scope. When dried, the mass of spores turned a dark amber 

 color and when sprayed with water the spore globules dissolved 

 and the spores collected between the necks of the perithecia, be- 

 tween the pustules, and in small fissures in the bark. When 

 drying they appeared first gelatinous and later granular. A 

 similar condition was observed on a specimen of bark sent in 

 after a heavy rain. Pycnospores are produced in enormous num- 

 bers and washed down the diseased trees during every winter 

 rain. These vary from a few thousand to several million. 



While working with the above specimens under the binocular 

 dissecting microscope the writer often observed nematodes 

 crawling over the surface of the bark where perithecia were 

 numerous. So frequently were their eggs found in the globules 

 of ascospores that the method of starting cultures from asco- 

 spores gathered from the perithecial necks had to be abandoned. 

 The cultures showed hatching nematodes *along with the germ- 

 inating ascospores. They were found living in the pustules, but 

 none were seen in the perithecia. 



