286 



MANUAL OF TREE DISEASES 



bark, and the spores within are shed as a fine powder. The 

 affected limbs of older trees may show but little swelling or, as 

 in the case of lodge-pole pine, large knots or galls and cankers 



are produced (Fig. 56). After the first 

 crop of blisters is formed, the bark 

 usually dies and the mycelium extends 

 its activities to the healthy bark around 

 the dead area. This process of en- 

 largement of the canker or gall con- 

 tinues until the limb or trunk is 

 girdled and death results. 



On the under sides of the leaves of 

 species of Castilleja, small yellowish 

 spots appear diu-ing the summer. 

 Later numerous brownish bristles are 

 pushed out from these spots. The 

 appearance of the leaf is very similar 

 to cm-rant and gooseberry leaves af- 

 fected with felt-rust (see page 277). 



Cause. 



The blister-rust which affects west- 

 ern pines and species of Castilleja is 

 caused by the rust-fungus Cronartium 

 coleosporioides { = Peridermiu'm,filainen- 

 tosum, the Rocky Mountain form of 

 Peridermium Harhnessii). The life 

 history of this rust is similar to that 

 of Cronartium ribicola described on 

 page 279. The seciospores germinate 

 and infect the Castilleja leaves. Ure- 

 diniospores propagate the fungus on this host throughout the 

 summer and the teliospores and basidiospores are formed iu 

 late summer. Infection of the pine takes place in the autunm. 



Fig. 56. — Blister-rust or 

 Castilleja rust on lodge-pole 

 pine. 



