190 



Mycologia 



Field observations made during 1910 seemed to point to Puccin- 

 iastrum arcticum on Rubus as the telial stage (Mycol. 3: 72. 

 191 1 ). It was also noticed that Uredinopsis mirabilis (Peck) 

 Magn. was associated in a very striking way with the same Peri- 

 dermium, but it was not considered probable that they were re- 

 lated. However, as observations made during the early summer 

 of 191 1 seemed to point to their connection, a sowing of the 

 Peridermium was made on a pot of Onoclea sensibilis on July 7. 

 Uredinia were observed abundantly on July 16. At this date the 

 filaments of urediniospores were oozing out. As the plants of 

 Onoclea were grown from rhizomes taken into the laboratory 

 in early spring, there was no chance for infection before the 

 sowing. Later study, however, suggested that urediniospores 

 may have been present on the Onoclea which grew beneath the 

 Abies shoots used in the culture experiment, and that infection 

 may have possibly come from urediniospores clinging to the 

 leaves. It was some time after the appearance of the Perider- 

 mium that the collection was made for the culture, so that there 

 was sufficient time for the urediniospores to appear on the ferns 

 even if they developed from the aecia on Abies. No record was 

 made at the time of collection of the presence of the fern rust, 

 but later it was abundant on the Onoclea beneath the fir and may 

 have been present at the time of collection of the aecia. 



On July 17 another sowing was made on a number of plants 

 of Onoclea sensibilis that had been obtained in the field on the 

 same day. Uredinia appeared on all about July 25. One pot of 

 plants kept as a check remained free from infection, but a few 

 plants of Onoclea in the field alongside of those that were used for 

 the culture showed uredinia on July 31. The possibility of the 

 plants being infected before being taken into the greenhouse is not 

 therefore excluded, so the experiment does not establish the con- 

 nection of the Peridermium and the fern rust. 



During the season the distribution of Peridermium balsameum 

 and Uredinopsis on ferns was carefully studied in the field and 

 their association was so marked that the writer concluded it 

 could not be accidental. There was evidence to show that more 

 species than one are included under this Peridermium. The first 

 appearance of the aecia was during the last week of June and the 



