Minnesota Plant Diseases. 



159 



Rusts (Uredinea). The rust fungi constitute a larger group 

 of plants than the smuts and exhibit more variety of structure 

 and habit. They may be considered as relatives of the smuts 

 in that the winter spores of the latter may be compared with 



rare grass rust s^ore (amphispore of 1'uccinia vcxans) germinating; it germinate* 

 as a summer spore, but has a thick coat and rests over winter as a winter spore. All 

 highly magnified. 1-5, after Ward; <J, after Carleton. (See also Fig. 74.) 



the smut spores The rusts, however, exhibit a great number 

 of accessory spore forms. They are all parasites and are of great 

 economic importance on account of the large number of dis- 

 ease-causing forms. The life-story of a rust plant is often very 



