THE ROSE RUST 115 



The Rose Rust 



Phragmidium mucronatum 



This is a distinct and easily recognized affection of 

 roses which has long been known, both in Europe and 

 America, to lovers of the queen of flowers. It seldom 

 attacks tea roses, usually confining its attention to the 

 hardy hybrid perpetuals. It generally appears early in 

 summer in the form of orange-yellow spots upon the 

 leaves, their petioles, or the green growing stalks. At 

 first these spots are small, but they grow in size, espe- 

 cially on the leaf petioles and young shoots, where they 

 generally become elongate, while the petioles and shoots 

 often become twisted and otherwise deformed. About 

 midsummer the orange-yellow color gives way to a brick- 

 red color, the latter appearing on the same spots and 

 being due to the production of a diiferent kind of spore. 

 Towards autumn still another kind of spore is produced, 

 developing in small blackish masses, mostl}'' on the 

 under sides of the leaves. These masses consist of the 

 so-called Avinter spores, which live over winter among 

 the fallen leaves, and in spring start the disease again. 



Microscopic Characters. — This is one of those 

 fungi which produce different spores at different seasons. 

 The spring form, producing the orange-yellow spots on 

 the leaves, is composed of the so-called wcidio-sjjores. 

 They are small spherical or angular bodies, which serve 

 for the rapid spread of the disease as they are blown 

 about by the wind. The spores forming the brick-red 

 spots of midsummer are called the uredo-spores. They 

 are borne on short pedicels, and though spherical in gen- 

 eral outline, have the outer surface roughened by numer- 

 ous projecting j)oints. One of the spores composing the 

 black spots found late in the season — called by botanists 

 the teleuto-spore — is represented at Fig. 52. It is very 

 different from either of the preceding forms, being cyl- 



