THE TAXONOMIC VALUE OF PORE CHAR- 
ACTERS IN THE GRASS AND SEDGE 
RUSTS^ 
J. C. Arthur and F. D. Fromme 
It is only in recent years that the germ-pores of the uredin- 
iospores of the rusts have been the objects of critical study by the 
mycologist. This study has been prompted by the desire to find 
additional morphological characters of sufficient constancy and 
clearness for taxonomic purposes. 
The first consistent use of urediniospore-pore characters in 
the description of rust species was made by the senior author of 
this paper in the second number of the North American Uredineae, 
issued in 1898 and printed in the Bulletin of the University of 
Iowa. They had occasionally been incorporated in descriptions 
prior to this but had not been used with any constancy. The pre- 
vailing tendency had been to regard all of the urediniosporic char- 
acters as of slight taxonomic value and to place the greater de- 
pendency on characters of the teliospores. The recent authors of 
systematic works on the rusts who have used urediniospore-pores 
most consistently are Fischer, Holway, Bubak and Grove. None 
of these authors, however, have incorporated these pore char- 
acters in their keys as has been done in the rust part of the North 
American Flora, the first number of which was issued in 1907. 
In no groups of the rusts has the taxonomist’s need of sharply 
distinctive morphological characters been more imperative than in 
those which have their uredinial and telial stages on grass and 
sedge hosts. These are included under two genera, Nigredo 
{Uromyces in part) and Dicaeoma (Puccinia in part) ; the former 
with one-celled and the latter with two-celled teliospores. There 
is a growing belief, which has been strengthened by the study of 
the urediniospore-pores, that there is no essential difference be- 
tween the two genera and that the presence of more than one cell 
1 Read before the Botanists of the Central States, at the St. Louis meeting, 
October 17, 1914. 
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