284 FUNGI 



rust is known to be capable of propagating year after year 

 in the uredo stage alone.^ the spores surviving through the 

 winter on volunteer grains and other grasses. 



406. Cedar Apples. — An excellent subject for study is 

 the common fungus {Gymnosporangiunt) that produces 

 upon red cedar twigs the large excrescences familiarly 

 known as " cedar apples." It is related to the wheat rusts, 

 but has only two phases, its spores germinating and pro- 



543. — Two species of " cedar apple " ( Gymnosporangium') , showing stage of the 

 apple rust fungus corresponding to the uredo-teleuto stages of wheat rust (from 

 Coulter's "Plant Structures"). 



ducing aecidia upon the leaves of apple, hawthorn, and 

 other kindred plants. In this stage it is known as Rostelia, 

 and is the cause of apple rust and other similar orchard 

 diseases. Specimens are generally easy to obtain and can 

 be studied by the same methods outlined in the foregoing 

 paragraphs. 



407. Polymorphism. — Plants that pass through different 

 stages in their life history are said to be polymorphic, that 



^ Bulletin 16, United States Department of Agriculture. 



