BRIEFER ARTICLES. 
TERMINOLOGY OF THE SPORE-STRUCTURES IN THE 
UREDINALES.: 
SOME time ago I began to study groups of species among the rusts in 
a more methodical way than usually pursued, and as part of the method 
undertook to prepare uniform descriptions in which like parts of each 
structure should receive the same kind of treatment in every case. I soon 
met with an obstacle that had not been anticipated. The terminology in 
use was found to be clumsy, ambiguous, poorly correlated, and quite inade- 
quate to show homologies properly. 
I will illustrate a few of the difficulties which confronted me. When 
an aecidium is mentioned, there is a tolerably clear conception of a cup- 
like structure filled with spores; but when one reaches the next stage of 
the rust, what is the meaning conveyed by the word uredo? I think it is 
most generally employed as a collective term, referring to the second stage 
of the rust. We can properly say that the uredo occurs on leaves of a 
certain host, but if we wish to specify a single uredinial structure correspond- 
ing to an aecidium, it is necessary to say uredosorus; and yet it is not per- 
missible to say aecidiosorus. Passing to the third stage of the rust there 
appears to be neither a specific nor a collective name with which to desig- 
nate it. The nearest approach to a specific term analogous to aecidium is 
teleutosorus, and to a collective term analogous to uredo is teleutostage. 
We can Say properly that aecidia appeared on a leaf, after a time they were 
followed by the uredo, and finally the teleutospore stage was developed; 
in which statement we have used three different methods to express the 
same idea relative to similar spore-structures. 
Taking up the first stage again, there appears to be nothing inappro- 
priate in calling the single spore-structure an aecidium so long as we have 
in mind the first stage of species belonging to the genus Puccinia or Uro- 
myces; but in the genus Phragmidium there is no peridium present, and in 
ymnoconia not only is the peridium absent but the spore-layer is extended 
and indefinite, and the term aecidium now seems far less applicable. For 
such cases it is customary to call the structure a caeoma, instead of an 
* Read before the American Mycological Society at Philadelphia, December 30, 
04. ' 
1905] 219 
