222 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
50 percent teleutosori, and only 5 less than that. Two of the cultures in 
this series never produced any uredospores whatever, teleutosori only being 
developed. It was obviously impossible to make transfers from such 
cultures. 
Figure 3, Plate XII, shows a rust mycelium in which only the first 
pustule produced uredospores, succeeding pustules bearing only teleuto- 
spores. 
Apparently there may be wide differences in the tendency towards the 
production of teleutospores in different cultures of a rust fungus, and the 
factor of fungous constitution should be given consideration in work on 
the conditions of teleutospore production. 
Nutrition and Growth Studies 
Water Cultures 
Six experiments were performed with Puccinia Sorghi on corn to test 
the effect on rust development of growing the host plants in culture solu- 
tions of varying nutritive value. A sugar corn was used, as being more 
susceptible to rust than a flint or dent corn. The seedlings were grown in 
water culture in 250-cc. Erlenmeyer flasks. Knop's nutrient solution was 
used as a base. Except as otherwise noted, the endosperm was removed 
about the time that the first leaf was breaking through the coleoptile, so 
that the plant was entirely dependent for sustenance on the mineral salts 
it could obtain from the nutrient solution and on the carbohydrates it 
could manufacture in its leaf tissue. Inoculation was effected by spraying 
with a suspension of uredospores and covering with a bell jar for 24 hours. 
Observations were made on the incubation period and on the progress of 
the disease on the plants. The dry weight of the top of the plant at the 
conclusion of the experiment was taken as an index of the relative vigor of 
growth of the plant. 
Table 5 
Exp. I. Effect of Renewing Solution. Plants Inoculated February 28, iqiq 
Drv Weight 
Observations 
No. of 
Treat- 
of Top 
Plant 
ment 
of Plant 
in Mg. 
March 9 
March 11 
March, 13 
I 
Solution 
3 pustules on 
I pustule on 
2 pustules on second 
changed once 
third leaf 
second leaf ; 
leaf; 3 pustules on 
a week 
3 pustules on 
third leaf 
third leaf 
2 
Solution not 
310 
No infection 
I pustule on 
I pustule on first leaf; 
changed 
second leaf 
4 pustules on second 
leaf; i pustule on 
fourth leaf 
3 
Solution not 
280 
No infection 
No infection 
I pustule on first leaf; 
changed 
I pustule on third 
leaf 
