THE RUSTS OF NOVA SCOTIA. FRASER. 357 



pedicels, fusiform, acute or beaked above, narrowed below; 

 wall colourless, thin, smooth except two opposite longitudinal 

 thickened ridges bearing single rows of minute projections, 

 not always evident when wet. 



Teliospores globoid, one to four-celled or more, usually with 

 intersecting septa; wall smooth, colourless, thin. 



This genus is found only on ferns. The species can usually 

 be recognized in the field by the yellow areas, on the lower side 

 of which the minute nredinia can be made out with a lens. 

 Often the small white filiform columns of urediniospores can 

 be seen, where they have emerged. 



The teliospores can be studied best by sectioning the leaf, 

 or if a small piece of the discoloured area be boiled for a few 

 seconds in lactic acid the spores can then be made out with 

 the aid of the microscope. Viewed from above they appear 

 circular with the walls (if four-celled) appearing as two 

 diameters at right angles. Viewed from the side they usually 

 appear two-celled. 



Dietel in "Engler and Prantl" regards the form, which 

 Arthur places for convenience as an aeciospore, rather as a 

 stalked teliospore, but its true position is not known. 



Arthur in the "North American Flora" describes seven 

 species, of these five are here described from Nova Scotia. 

 The other two have been reported only from the Pacific coast. 



From careful field study the writer believes that the fern 

 rusts belonging to this genus are heteroecious, the aecidial 

 stages in some species being found on Abies balsamea. This 

 matter is discussed further under Peridermium balsameum. 



Uredinopsis Osmundae Magn. 



I. Aecia unknown. 



II. Uredinia hypophyllous, on yellowish spots, usually 

 bounded by veins, small, roundish, dehiscing by central open- 

 ing, spores exuded in a white filiform column. Urediniospores 

 oval or fusiform, sometimes clavate, 10-19 by 31-52/x, acute or 



