18 



MASS. EXPERIMENT STATION BULLETIN 368 



infection without wounding. This again indicates the possibility of the disease 

 being spread by insect vectors. 



B 





howing hyphae of the causal fungus in the 



Experiment 4. 



Procedure: — Another series of inoculations was carried out with fifteen 

 different isolations of the fungus. These cultures were used directly from isola- 

 tions without any attempt to obtain single-spoie cultures. All of the cultures 

 were less than a month old. 1 iioculations were made on seedlings of U. americana 

 L. by the agar insertion nielliod. Roots also were inoculated by placing a small 

 block of fungus-laden agar on the root tissue from which the epidermis had been 

 scraped. Following this operation the soil wiiicli iiad been removed from the 

 roots was carefully replaced. These inoculations were made August 10, 1936. 



Results: — Twigs from the inoculated trees, which showed symptoms of the 

 disease, were collected December 15, 1936, and used for tissue plantings. Seven 

 trees died back and from si.K of these seven the fungus was leisolated. The 



