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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 25o-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, 1919. 



