340 THE RUSTS OF NOVA SCOTIA. FRASER. 



value." He adds that bis classification has to do fundament- 

 ally with the progressive evolution of the rusts and not with 

 adaptations; thus the genus Dasyspom includes species that 

 have progressed in their evolution to the stage where aecio- 

 spores and urediniospores have been effectively suppressed 

 from the life cycle. Such a classification demands a more 

 intimate knowledge of the rusts and more insight into their 

 life history than the old system which was based largely on 

 the structure of the teliospores. 



He also states that there are some short cuts that 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 pycnia 

 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 mycelium, it may safely be assumed that no uredinia 

 belong to the life cycle. Furthermore it rarely or >neve?r 

 happens that teliospores of the Uromyces-Puccinia type, 

 germinating immediately on maturity, belong to genera with 

 other spore forms in the life cycle, excepting some largely 

 tropical genera. Short cuts are also available in other direc- 

 tions. All gramineous and cyperaceous hosts bear rusts that 

 inay be assumed to possess all spore forms and are heteroecious. 

 Qnly one exception is known at present." 



In the following pages the species occurring in Nova Scotia 

 are described. The classification is largely that of Dietel in 

 "Die Natiirlichen Pflaiizenfamilien/' While it might be better 

 tjo follow Arthur's classification, as he has made the most 

 extensive and thorough study of !N"orth American rusts, yet 

 his work has not progressed far enough to make thait possible 

 in all cases, so for the present the classification that follows 

 has been adopted. 



