Nov., 1921] MAINS RUSTS ON NYSSA AND URTICASTRUM 
Kuehneola line may possibly be considered as representing an original 
potentiality in the ancestral type which developed in Melampsoropsis but 
which in the Aplopsora-Kuehneola line became gradually weaker. Phakop- 
sora with the delayed germination of its teliospores may be considered as 
a similar but less fully developed line from a source similar to that giving 
rise to Cerotelium. 
Both the rusts described above have offered considerable difficulty in 
the determination of their generic position. It is in this, however, that their 
principal interest lies, for such species are to be expected as the result of 
evolutionary development and from such our knowledge of relationships 
must be obtained. With our present imperfect knowledge of the rusts of 
the family Melampsoraceae, it is perhaps impossible to gain more than a 
suggestion of the possibilities which exist. It is felt, however, that these 
two rusts, Aplopsora Nyssae and Cerotelium Dicentrae, in their evident 
relationships point to lines of development, the importance of which will 
have to be left for future information and studies fully to bring out. 
To Prof. H. W. Anderson credit is due for the discovery of Cerotelium 
Urticastri and for the trouble he has taken in solving the life history of 
this rust. The writer wishes to express his appreciation to Dr. J. C. Arthur 
for the opportunity of studying the Urticastrum material and for advice 
and criticism in the study of these two interesting rusts. To Prof. H. S. 
Jackson acknowledgment is due for aid in obtaining additional material of 
Aplopsora Nyssae in the New York Botanical Garden herbaria and for 
helpful criticism of this work. 
Purdue University Agricultural Experiment Station, 
Lafayette, Indiana 
