80 Journal of thk Mitchkll Society [Scptcmhrr 



vestigal nuecllai- tissue. TJie liyphae will be noted to be present in all 

 of these tissues which make up the seed coat and to extend into the 

 storag-e tissues of the cotyledons beneath, Fig. 12-e. 



The initiation of the disease in fields not previously seeded to vetch 

 is due to the planting of infected seed. This is supported by field 

 observations during the past two seasons and by an experiment 

 planned to determine this point. Seed from affected pods were col- 

 lected b.y the writer in the spring of 1918, and were sown in a new 

 field. By April 15th of the following spring, the plants were abun- 

 dantly diseased. 



The organism can remain alive during summer on old affected 

 parts which undoubtedly serve as a source of infection where vetch 

 is permitted to reseed itself. No evidence has been secured that the 

 organism possesses any other than the conidal stage although repeated 

 examination has been made throughout the entire year of material 

 kept out of doors in wire baskets. Were an ascigerous stage formed, 

 it is not believed that it could have escaped detection. Furthermore, 

 reproduction by conidia alone has occurred in cultures on the various 

 media previously mentioned. Some of these cultures have been main- 

 tained for an entire year without transfer but with the addition of 

 sterile water to replace that lost to evaporation. 



Infection Experiments 



The organism is such a virulent parasite, as indicated by field 

 observations, that little attention has been given to infection experi- 

 ments except to study the manner of infection. Three series of inocu- 

 lations were effected, however, upon plants grown in the greenhouse. 

 Two were made with a crude inoculum consisting of the water in which 

 diseased plants had been washed. This water was atomized upon 

 healthy plants and characteristic lesions developed within ten days. 

 The other was made with pure cultures of the organism grown on 

 agar. A watery suspension of conidia was in this case apj^lied with 

 an atomizer to healthy plants on May 19. The plants were then 

 shaded for 24 hours with a sheet of paper. By May 29 acervuli had 

 matured on the stems and leaves of these inoculated plants. 



Host Plants 



Frotocoronospora nigricans appears to be limited to species of 

 Vicia. It has been observed to be very destructive to Vicia sativa 



