422 FUNGOUS DISEASES OF PLANTS 



of any rust. The spermogonia are extremely numerous, cover- 

 ing practically both surfaces of the leaf, while the uredo and 

 teleutosporic sori occur on the under surface of the leaves only. 

 In the first generation the sori are confluent, but in the second 

 generation distinct. This species occurs on the common Canada 

 thistle (Cirsium arvense). Infection from the teleutospores pro- 

 duces a mycelium which deforms the host, but the infection from 

 uredospores produces a localized mycelium. These differences upon 

 the same host suggest a condition which may be regarded as bio- 

 logically intermediate between true autoecism and hetercecism. 



Puccinia Hieracii (Schum.) Mart. This rust occurs on various 

 species of Hieracium, and from the observations made it would 

 also appear to be a species embracing many different forms. 



Puccinia fusca Relhan. This rather variable species is parasitic 

 upon certain anemones, and the mycelium has been experimentally, 

 determined to be perennial in the host. 



XX. GYMNOSPORANGIUM 



FARLOW, W. G. Notes on Some Species of Gymnosporangium and Chryso- 



myxa in the United States. Proc. Amer. Acad. Arts and Sci. 20 : 3 1 1-323. 



1885. 

 FARLOW,W. G. The Development of the Gymnosporangia of the United States. 



Bot. Gaz. 11 : 234-241. 1886. 

 FARLOW, W. G. The Gymnosporangia (Cedar-Apples) of the United States. 



Anniv. Mem. Boston Soc. Nat. Hist. 38 pp. 2 pis. 1880. 

 PAMMEL, L. H. The Cedar Apple Fungi and Apple Rust in Iowa. Iowa Agl. 



Exp. Sta. Built. 84: 1-36. 1905. 

 RICHARDS, H. M. The Uredo-stage cf Gymnosporangium. Bot. Gaz. 14 : 



211-216. pi. 77. 1889. 

 THAXTER, R. Notes on Cultures of Gymnosporangium made in 1887 and 



1888. Bot. Gaz. 14: 163-172. 1889. 

 THAXTER, R. The Conn. Species of Gymnosporangium (Cedar-Apples). 



Conn. Agl. Exp. Sta. Built. 107: 1-6. 1891. 



There is, perhaps, no genus of rust fungi comprising several or 

 more species which is as uniform in developmental processes as 

 the genus Gymnosporangium. Aside from a direct agreement in 

 the sequence of spore forms, and in the general relations of these 

 forms one to another in the different species, all have the same 

 spore forms, namely, spermogonia, aecidia, and teleutospores ; and 

 in the different species the same spore forms appear in almost 

 the identical season. 



