2l6 
E. B. MAINS 
atmosphere favor the development of the rust and increase the number 
of spores formed. 
3. Puccinia coronata and Puccinia Sorghi do not appear to injure 
the cells of the infected area. The injury produced appears first in 
the areas surrounding the infected regions. This is probably due to a 
starvation brought about by a withdrawal of food from them by the 
infected areas. 
4. A starvation of the host of various elements does not bring about 
immunity from the rust, but reduces the quantity of the rust produced. 
5. Light is not necessary for the development of Puccinia coronata 
and Puccinia Sorghi when the host is able to obtain a good food supply. 
6. When deprived of carbohydrates, light is necessary for the 
development of Puccinia coronata and Puccinia Sorghi in that it is 
necessary for the formation of carbohydrates by the host. 
7. When deprived of carbon dioxide, the development of Puccinia 
Sorghi is stopped due to a lack of carbohydrates in the host. 
8. Pure cultures of Puccinia Sorghi can be maintained upon both 
sterile seedlings and upon pieces of Zea Mays leaf floated upon car- 
bohydrate solutions. 
9. Puccinia Sorghi develops and forms spores upon seedlings or 
cut pieces of corn leaf when these are supplied with starch, cane sugar, 
dextrose, maltose, and dextrin in the dark. 
10. When either seedlings or pieces of corn leaf are exhausted of 
carbohydrates and supplied only with mineral nutrient or water, 
Puccinia Sorghi is not able to develop in the dark. 
11. Puccinia Sorghi is not able to use maltose, dextrose, cane sugar, 
asparagine, leucine, peptone with and without mineral salts, or decoc- 
tions of. the host when supplied to it directly. 
12. The obligate parasitism of the rusts is probably explained by 
their requirement of some transitory or nascent organic products 
related to the carbohydrates which they obtain in the living host. 
VI. LITERATURE CITED 
Acton, E. H. 
1889. The Assimilation of Carbon by Green Plants from Certain Organic 
Compounds. Proc. Roy. Soc. London 47: 150-175. 
Balls, W. L. 
1905. Infection of Plants by Rust Fungi. New Phytol. 4: 18, 19, 
Bary, A de. 
1853. Untersuchungen iiber die Brandpilze. Berlin. 
1863. Recherches sur le developpement de quelques champignons parasites. 
Ann. Sci. Nat. IV. Bot. 20: 1-148. 
