290 BOTANICAL GAZETTE [APRIL 
each, while on the genus first mentioned 25 species are here recog- 
nized. All of the species, so far as known, are autoecious, although 
the full life history has been determined for only a few. There are 
a number of unconnected species of Aecidium and Uredo recorded 
which are not discussed in this account. While it is possible that 
some of the former may belong to heteroecious species, there is no 
supporting evidence available. 
The large number of species occurring on Vernonia and the 
great variation in morphological characters and in life history which 
they exhibit are perhaps unparalleled on any other host genus in 
this group of rusts. When we consider, however, that the most 
important influencing factor in the evolution of the parasitic fungi, 
particularly in a group as highly specialized as the rusts, is undoubt- 
edly that of the host, it is perhaps to be expected that a genus of 
hosts which includes an estimated number of 600 species, many of 
which show great variation, should harbor a large number of species 
of closely related parasites. The genus Vernonia occurs in bo 
the Eastern and Western Hemispheres, over a wide range of lati- 
tude and under almost every conceivable condition of climate and 
range of elevation. 
It is noticeable that the species of rusts under discussion are 
more numerous in the subtropical than in the temperate regions. 
For example, while but one species of Puccinia occurring on 9 
species of Vernonia is known in the United States, 10 species 
occurring on 8 hosts are known from Guatemala and Costa Rica. 
Three host species, V. patens, V. leiocarpa, and V. triflosculosa, 
harbor two species each in the latter region. There are 17 different 
species recognized from North America, of which 4 have been 
collected in Mexico, 5 in the West Indies, and ro in Guatemala and 
Costa Rica; 8 are known from South America and 3 from the 
Eastern Hemisphere; 2 species only are indigenous to both North 
and South America. 
All of the material in the Arthur herbarium at.the Purdue 
University Agricultural Experiment Station and in the herbarium . 
of the New York Botanical Garden has been available in making 
this study. In addition, a very remarkable collection of uniden- 
tified specimens made by Professor E. W. D. Hotway in Guatemala 
