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 (191 5), who con- 
siders that the determining factor is the physiological aging of the host 
tissue, 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 
