316 MANUAL OF TREE DISEASES 



urediniospores develop. Later in the autumn small bright 

 red or yellowish clumps of teliospores are formed on the leaves 

 and these spores over-winter and produce basidiospores in 

 the spring. These latter spores infect the young spruce needles. 

 The affected needles become yellowish and soon produce two 

 irregular rows of white blisters on the under surface. 



The three species of closely related rust-fungi causing these 

 diseases were known by the following names for the stage on the 

 spruce before the stages on the heath plants were connected 

 with them: Peridermium abietinum (Alb. and Schw.) Thiim. 

 = M. abietina (Alb. and Schw.) Arthur ; P. decolorans Peck 

 = M. ledicola (Peck) Arthur ; P. cansimUe Arthur and Kem 

 = M. cassandroB (Peck and Clinton) Arthur. 



References 



Arthur, J. C, and Kem, P. D. North American species of Peri- 

 denmum. Bui. Torrey Bot. Club 33 : 403-^38. 1906. 



Fraser, W. P. Cultures of some heteroecious rusts. Myeologia 3 : 

 67-74. 1911. 



Fraser, W. P. Cultures of heteroecious rusts. Mycologja 4 : 175-193. 

 1912. 



Clinton, G. P. Heteroecious rusts of Connecticut having a Perider- 

 mium for their secial stage. Connecticut Agr. Exp. Sta. Ann. 

 Rept. 1907-1908 : 369-396, pis. 25-32. 1908. 



Leaf-Rust 



Caused by Chrysomyxa Weirii Jackson 



The leaves of Engelmann spruce are affected by a rust disease 

 in the Northwest. This leaf-rust differs markedly from the 

 blister-rusts of spruce (see page 315). The affected needles 

 show yellowish spots on which develop prominent orange or 

 brownish waxy pustules which break through the epidermis. 

 The teliospores formed in these pustules germinate and produce 

 basidiospores which infect other spruce needles. No alternate 

 host is required in the life history of this rust and the JBciospore 

 and lurediniospore stages are omitted. 



