RUST-FUNGI. 



245 



soon shed (Fig. 62), while the Cseoma-stage is spent on Conifer leaves 

 (Pines, Firs, and Larch). 



In the genus MelampsoreUa the intermediate form is called JEcidium, 

 and the chief disease is M. cerastii, producing round orange-yellow pustules 

 on the leaves of plants belonging to the Alsinece family (and especially 

 Cerastium, Stellaria, and Holostea] which 

 develop the resting - spores producing Fig. 62. 



JEcidium elatinum on the Silver Fir, either 

 as spindle-shaped cankerous excrescences on 

 the stem, or twig-clusters with yellow-green 

 deformed foliage ("witches' brooms") on 

 branches. It perenniates and often kills 

 trees infected, especially in hot dry years 

 and on sandy soil. 



Whether a canker-spot or a twig- deformity 

 will be produced depends on where the 

 spores enter and the mycelium develops, 

 but both are often found on a tree. If 

 infection takes place near a healthy bud, a 

 deformed twig-cluster results ; but if the 

 mycelium infects the bark of a shoot, canker 

 is produced, infection being only possible 

 through some wound-surface. The yellow 

 or brownish - orange 

 cecidiospores are pro- 

 duced in the diseased 

 leaves of the young- 

 est shoots in the 

 twig - clusters, and 

 appear from June till 

 August on the lower 

 side. The ^Ecidium 

 perenniates and in 

 course of time the 

 canker-swellings and 

 the twig-clusters at- 

 tain a large size. 

 The disease can only 



Willow Rust on Osier. 



a. Green leaf with yellow pustular sporophores. 



&. Dead parts of leaf. 



c. Sporophores on the osier-stem. 



be eradicated by con- 

 tinuously cutting off and burning the twig-clusters in June and July 

 before their spores ripen by pruning infected branches, by thinning out 

 cankered poles or trees, and by removing and burning the host-plants 

 (Cerastium, Stellaria, Holostea) '^upon which the M. cerastii develops 

 resting-spores. Anotner disease of the sam genus is M. betulina + ^Ec. 



