188 
Journal of Mycology 
[Vol. 12 
/ A NEW CLASSIFICATION OF THE UREDINALES. 
BY J. C. ARTHUR. 
Separates of the paper on Eine Klassidkation der Uredineen, 
read by the present writer before the International Botanical 
Congress at Vienna in July, 1905, were distributed early in Au¬ 
gust of the present year to many Journals and Libraries, and 
to a large number of mycologists. Some of the phylogenetic 
reasons which are made the basis of this latest attempt at a 
natural arrangement of the genera of rusts have been more or 
less fully stated in other communications already before the pub¬ 
lic. The present occasion may be seized to state some of the 
aids and difficulties that will beset the practical acceptance of 
the classification. 
The simplicity of the old order of things disappears in this 
new arrangement, and herein will doubtless arise one of the 
strongest protests against it. When nine-tenths of all forms of 
rusts usually met with were easily assigned to the Uromyces- 
Puccinia group, and if they had one-celled teliospores were 
species of Uromyces, or two-celled teliospores were species of 
Puccinia, or if they happened to be aecia were species of Aecid- 
ium, the naming of rusts seemed an easy matter to the casual 
student. But in the new system it is essential that something 
of the life history be known, including the number of spore forms, 
and the structure of the sorus. Before, any species with a two- 
celled, stalked teliospore might be safely called a Puccinia; but 
now, such a species may rest in any one of thirteen genera. 
Before, it did not matter whether pycnia (spermogonia) accom¬ 
panied the telia, or other spore stages, or not; but now such 
association is often of fundamental importance in the location of 
a species in the system. Heretofore, the structure of the uredin- 
iosorus has been of slight systematic value; now, examination 
of this feature alone may place the species in the correct genus, 
or within a small group of genera. Such requirements for the 
naming of collections necessitate a more intimate knowledge of 
the rusts as a whole, some insight into their life-history and 
some appreciation of their structure. For this reason the system 
may not for a time prove as acceptable as the one in present use. 
There are, however, some short cuts to sufficient informa¬ 
tion to enable one to name his collections. Thus, telia associated 
with pycnia may be safely assumed to belong to a genus in which 
aecia and uredinia are wanting, or at most so little developed 
as to be of no taxonomic importance. In like manner pvcnia 
associated with uredinia, the so-called primary uredinia, may be 
assumed to indicate a genus in which aecia are wanting. If 
aecia show telia arising within or about them from the same 
