CULTURES OF HETEROECIOUS RUSTS 



W. p. Fraser 



The cultures described in the following pages were undertaken 

 during the spring and early summer of 191 1. Special attention 

 was given to the study of the aecia on conifers and their connec- 

 tion with telial forms, but a few cultures of the grass and sedge 

 rusts that field observation suggested were also tried. The success 

 attained was largely due to the excellent opportunity for field 

 observation that the region afforded and the ease with which 

 material could be collected. 



The teliosporic material used in the cultures was collected in 

 the districts surrounding the town of Pictou. The greater part 

 was obtained in the spring, but considerable material was col- 

 lected the previous fall and was left exposed to the weather during 

 the winter in small cheese cloth bags. When the host plants were 

 ready for infection, the leaves or parts of the plants bearing telia 

 were placed in a moist chamber on damp blotting paper and then 

 sprayed with water by means of an atomizer. When it was found 

 by examination that the teliospores had germinated, the germi- 

 nating teliosporic material was suspended above the host plants 

 so that the basidiospores would fall on the leaves, the whole was 

 then sprayed by an atomizer and covered for from one to several 

 days with a bell jar. This method was satisfactory except that 

 it frequently gave such rich infection that the plants were killed 

 by the abundant pycnia. In all cases the teliospores were found 

 to be germinating before the sowing was made unless stated other- 

 wise in the descriptions. Sometimes it was found that the telio- 

 spores did not germinate in the moist chamber for several days; 

 in some cases five to seven days were required for germination, 

 in others a day or less was sufficient. The teliospores of the 

 Melainpsoropsis rusts, which mature and germinate on the living 

 host plants in the spring, were collected when germinating, or 

 the mature telia were placed immediately after collection in a 

 moist chamber until they germinated freely, which usually took 

 place in about twenty-four hours. 



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