May, 1922] RAINES VEGETATIVE VIGOR OF THE HOST 221 



of the uredospores under the conditions of inoculation was from 75-90 

 percent, and that it is possible for a single spore to produce infection, we 

 can say that (taking the conservative germination figure of 50 percent) of 

 more than fifty spores germinating on the surface of the leaf, only one 

 produced successful infection. Evidently, successful infection~by a uredo- 

 spore involves other factors besides that of germination on the leaf surface 

 of the host plant. 



The Constitution of the Fungous Mycelium as a Factor in Teleutospore 

 Production by Puccinia coronifera 



Our knowledge of the conditions governing teleutospore production in 

 the cereal rusts is summarized and extended by Gassner (1915), who con- 

 siders that the determining factor is the physiological aging of the host 

 tivssue, teleutospore production being particularly coincident with the 

 mobilization of the food resources of the plant for flower and fruit produc- 

 tion. The picture of teleutospore production presented by the plants of 

 the experimental field plots described above closely parallels Gassner's 

 observations in similar experiments and is consistent, with his views. 



Consideration of the behavior of Puccinia coronifera as regards teleuto- 

 spore production, when grown in the greenhouse, leads to the suggestion 

 that the protoplasmic constitution of the fungous mycelium may be a factor. 

 Greenhouse cultures of the rust from material brought in from the field in 

 the vicinity of New York exhibited moderate teleutospore production. A 

 series of cultures from material sent the writer by J.I. Durrell from Ames, 

 Iowa, on the other hand, grown at the same time on similar host material 

 and under similar conditions, showed very abundant teleutospore produc- 

 tion, the difference in this respect between the two series of cultures being 

 readily noticeable. While such teleutospore production on potted oat 

 seedlings in the greenhouse is more commonly on the older infected leaves, 

 which are yellowing at the tip, it is not unusual to observe the production of 

 teleutospores by rust pustules on young and vigorous leaves shortly after 

 first infection. 



Experiment showed that it is readily possible to secure variation in the 

 tendency of the rust towards teleutospore production by selection. The 

 rust was grown in test tubes under aseptic conditions. Large variation in 

 the tendency towards teleutospore production was noted in cultures of the 

 third generation, some rust cultures showing no teleutosori at all; in others 

 as much as 75 percent of the pustules were teleutosori. Two series of 

 cultures were therefore propagated. In one of the series, transfers were 

 made from cultures showing no teleutospores. Of 36 cultures in this series, 

 20 showed complete absence of teleutosori ; only 2 of the cultures developed 

 more than 50 percent of the winter stage. 



In the second series, transfers were made from cultures showing 75 

 percent teleutosori. Of 35 cultures in this series, 30 showed more than 



