THE NATURE AND DEVELOPMENT OF THE PRIMARY 
UREDOSPORE. 
A. H. CHRISTMAN. 
(With Plate XXIX) 
The true interpretation of the peculiar fertilization phases 
in the life cycle of certain of the rusts as discovered by Black¬ 
man (1) and the author (3) will certainly not be reached with¬ 
out the study of a great number of forms, including especially 
those species with an abbreviated life cycle. The studies de¬ 
scribed here are intended as a further contribution in this line, 
taking up the special case of the development of the so-called 
primary uredospore. 
Phragmidium potentillae canadensis Diet, is a form in 
which the aecidium is commonly supposed to be lacking, and 
the so-called primary uredospores result from an inoculation 
with sporidia from the teleutospores, while the secondary ure¬ 
dospores occur later as a result of infections from primary ure¬ 
dospores. 
The hyphae of the primary uredospores differ from those that 
produce the later uredospores, in that they apparently also pro¬ 
duce spermatia while those of the secondary uredospores do 
not. In structure, too, there is a difference. Those hyphae 
associated with the spermatia, in every case that I have ob¬ 
served, are composed of uninucleated cells, while the mycelial 
cells of stages unaccompanied by spermatia have regularly two 
more compact and smaller nuclei. 
