PAPERS ON BOTANY 131 



STUDIES IN PHYLLOSTICTA AND CERCOSPORA. 



ESTHER YOUNG, UNIVERSITY OF ILLINOIS 



During the years 1912 and 1913, while Dr. F. L. Stevens 

 was clean of the College of Agriculture and Mechanic Arts 

 in Porto Rico, he made extensive collections of parasitic fungi. 

 When he came to the University of Illinois, he donated this 

 collection to the University. In my studies I have made use of 

 this material, working chiefly on the two genera Cercospora 

 and Phyllosticta, both of which belong to the group of Im- 

 perfect Fungi. 



The genus Cercospora of about 700 species, contains many 

 important parasites, chiefly causing leaf-spotting. The spots 

 are variable in size and color, often bordered by a narrow red- 

 dish or purple margin, with a sordid-white center due to the 

 fungal hyphae which penetrate into the leaf. The spots are 

 usually definite, though in some instances indefinite, or even 

 lacking when the leaf is covered with a smoky brown mass. If 

 conditions are such that growth is abundant, the spots become 

 hoary, due to the large number of spores. The fruiting bodies 

 are conidia which are borne on the ends of hyphae or conidi- 

 phores, which vary in number and size, may be simple or 

 branched, and are brown in color. They are often abruptly 

 bent at the point of spore production, and thus conidial scars 

 are left. Conidiophores are usually fasciculate, and may arise 

 singly or in numbers from the stomata of the leaf. As a rule, 

 they vary in length and septation with age. The conidia are 

 hyaline, several septate and they vary in size and shape. They 

 are usually elongate, clavate or fusoid, straight and sometimes 

 attenuate at the end farthest from the conidiophore. Each 

 cell of a conidia is capable of germination, and very often 

 when spores fall on a leaf, they produce germ-tubes which in- 

 fest the host through the stomata. Very few cross inocula- 

 tions have been made, and, little is really known concerning 

 the limitations of the species. When the host plants are dif- 

 ferent, minor variations in size, color, septation, etc., of the 

 conidia and conidiophores, or in the macroscopic appearances 

 of the spots are generally employed in distinguishing species. 



The genus Phyllosticta is very large, comprising nearly 

 1200 species, only a few of which have been determined by 

 comparison or cultural studies. These forms produce leaf 

 spots which may be circular, angular or indefinite. This 

 genus differs from Phoma in that it inhabits only the leaves, 

 while the latter may spread over the fruit, twigs or stems, also 

 in that Phoma never produces a definite spot. The leaf blotch 



