Fraser: Cultures of Heteroecious Rusts 183 



Melampsoropsis Pyrolae (DC.) Arthur 



The association of this rust with Peridermium conorum-Piceae 

 (Rees) Arthur was discussed in a previous paper (Mycol. 3: 70. 

 191 1 ). This season's experiments were carried on for the pur- 

 pose of estabHshing the connection of these forms. 



Three trees of Picea mariana (Mill.) BSP. were taken into the 

 laboratory just when the cones were bursting the scales, and on 

 May 26 plants of Pyrola bearing germinating teliospores were sus- 

 pended above so that the basidiospores would fall on the cones. 

 Two of the trees soon died, the third grew for a time and the 

 cones developed. Pycnia were noticed on June 17, followed by 

 the aecia of Peridermium conorum-Piceae. The aecial spores 

 were being shed by July 16. Only one cone became infected, out 

 of about fifteen that grew on the tree. 



Experiments were also tried in the field. Two trees about 

 fifty yards apart were selected in a grove of Picea on a point that 

 juts into the harbor. The grove was surrounded on the land- 

 ward side by cultivated fields and was a mile or more distant from 

 any suspected source of infection. Plants of Pyrola bearing ger- 

 minating teliospores were suspended on May 29 above the cones 

 as in the experiment in the laboratory, provision being made to 

 keep their roots moist. On June 26 the cones of both trees were 

 covered with pycnia which probably appeared a week or more 

 earlier, as only occasional visits were made to the place. Aecia 

 were present by July 4 and the spores were being shed by July 8. 

 One of the trees was Picea mariana; of the 21 cones that it bore, 

 all but one were infected. There were 14 cones on the other tree 

 {Picea canadensis) , of which 9 were infected. The cones of the 

 trees {Picea) that grew everywhere near were carefully examined 

 and no infection was found in the vicinity or within more than 

 a mile of the place where the experiments had been made. When 

 the aecial spores are being shed the infected cones are conspicuous 

 and not likely to be overlooked especially on small trees. Even 

 the pycnial stage is also conspicuous as the scales turn yellow, 

 and yellow-colored resin oozes freely from the cones. The most 

 of the trees in the grove were small, not over 20 feet in height, 

 but cones were plentiful. For convenience, the smallest trees 

 with few cones were selected for the experiments. 



