Fraser: Cultures of Heteroecious Rusts 69 



the spores of Peridermium consimile on Chamaedaphne calycu- 

 lata and the uredinial stage of Melampsoropsis Cassandrae ap- 

 peared. This seems to be the only previous attempt to establish 

 the connection of these forms. 



Melampsoropsis abietina (Alb. & Schw.) Arthur 



The uredinial stage of this rust was very common on Ledum 

 groenlandicum Oeder in the summer of 1909, and many collections 

 of aecia were made on the spruces near, which seemed to belong 

 to the form on Ledum, but as no telia were collected the connec- 

 tion appeared doubtful. The next spring telia were found to be 

 very common on the under side of small, thin leaves of Ledum, 

 from which the tomentum was absent. The teliospores were 

 germinating freely the second week of June, the first collection 

 being on June 10. At this time the young shoots of Picea rubra 

 and P. mariana were opening, those of P. canadensis having 

 opened about a week earlier. 



On June 16 sowings were made on Picea rubra (DuRoi) Dietr. 

 Pycnia appeared abundantly on June 25 and abundant aecia soon 

 followed. Four trees were used and the infection was pro- 

 nounced on all of them. The aecia were found on examination 

 to be Peridermium. abietinum (Alb. & Schw.) Thiim. Two 

 plants of Picea obtained in the same place as those used for the 

 cultures were kept as controls and remained free from aecia. 



In the field, pycnia and aecia developed on the spruces that 

 grew near the telia-bearing Ledum. This was observed in many 

 places, though sometimes M. ledicola was near and a possible 

 source of infection. In one place where there was abundant 

 germination of the telia of M. abietina and no other rust was in 

 the vicinity, the aecial infection on the spruces near was very 

 pronounced. A collection from this source was made on July 

 17 and part of it was sent to Dr. Arthur. He reported the col- 

 lection as Peridermium abietinum (Alb. & Schw.) Thiim. and 

 the host as Picea rubra (DuRoi) Dietr. 



All the forms of this rust are very common in the vicinity of 

 Pictou. The telial stage was often found occurring on the same 

 plants as M. ledicola, but was much more common than that 

 species. 



