130 MAXUAL OF TREE DISEASES 



(Pyrus). The teliospores borne on the brown cushions gei> 

 minate and the basidiospores which are formed in this process 

 are blown away and cause the infection of the chokeberry 

 leaves, ^ciospores produced on this host plant then cause 

 infection of the cedar leaves later in the season if they 

 chance to lodge on them. A more detailed explanation of 

 the life history and control of the rust-fungi belonging to the 

 same genus as this pathogene will be found imder junipter dis- 

 eases, on page 192. 



Western Leaf-Rust 



Caused by Gymnosporangium nootkalensis (Trelease) Arthur 



Along the Pacific Coast in the Northwest, the yellow cedar 

 is affected by this leaf-rust. The symptoms are similar to the 

 eastern leaf-rust described above. The life history of the causal 

 pathogene is completed on the leaves of species of apple and 

 mountain ash. For a more detailed description of the habits 

 and control of the rust-fungi of this genus, see under eastern 

 leaf-rust, above, and juniper diseases, on page 192. The life 

 history of this rust-fungus differs, however, from all of the 

 other species of the genus GjTunosporangium, in that uredinio- 

 spores are formed on the cedar leaves. The teliospore-cushions 

 have not been found but undoubtedly occiu- on the cedar 

 leaves associated with the lurediniospores. 



Bkown Felt-Blight 

 Caused by Herpotrichia nigra Hartig 



Incense cedar is one of the many conifers subject to this 

 disease in the Northwest. The leaves and twigs are covered 

 with a dark brown mat of mycelium (Fig. 16). The mycelium 

 also enters the leaf-tissues. Young trees and the lower branches 

 of older ones are killed and imder conditions favorable for the 

 development of the causal fungus, the trees appear as scorched 



