PR( ) rOBASIDIOMYCETES 423 



There are about fifteen species of these fungi, all but one of 

 which have the aecidial or rust stage (Rcestelia) on some member 

 of the tribe Pomeae, generally apple, pear, or crab (Pyrus), quince 

 (Cydonia), shad bush or service berry (Amelanchier), or hawthorn 

 (Crataegus). The teleutosporic stage, which is commonly produced 

 on hypertrophied parts in the nature of " cedar apples," witches' 

 brooms, and other deformities of the host, generally occurs upon 

 one of the species of red cedar or juniper (Juniperus) ; only two 

 species of these fungi are exceptions, these having as a host the 

 related genus Cupressus. These fungi are of economic interest 



FIG. 205. ^ECIDIAL STAGE OF GYMNOSPORANGIUM ON FRUIT OF HAW 



because of the injuries to fruits and leaves of the Pomeae, and 

 not as a rule because of serious injuries to the coniferous hosts. 

 f On account of the great similarity in development, the general 

 facts of life history import may be collectively presented. More- 

 over, since in the order of season the teleutosporic form occurs 

 first, the discussion will follow this plan. 



Soon after the growing season begins, and following a warm 

 rain, there will be found protruded from the cedar apples, or from 

 enlargements on the twigs of other conifers mentioned, gelatinous, 

 orange-colored spore masses, sometimes horn-like, and again almost 

 shapeless. These masses consist, in large part, of orange-tinted 



