S22 



THE BASIDIOMYCETES 



Fig 12. Stages in development of the uredinium of Cronartinm ribicola. 

 (Adapted from Colley.) A. Subepidermal primordium composed of bi- 

 nucleate cells B. Layer of cells, destined to become urediniospores, formed 

 on outer surface of primordium. C. Urediniospores liberated by rupture 



of overlying host tissue. 



