u 



PLAKT STEUCTUEES 



disease with great rapidity (Fig. 50). Once it was thought 

 that this completed the life cycle, and the fungus receiTcd 

 the name f "redo. When it was known that this is but one 



Fig. 50 —Wheat rust, ehowing a young hypha forcing its way from the surface of a 

 leaf down among the nutritive cells.— After H. Maeshall Wakd. 



stage in a polymorphic life history it was called the Uredo- 

 stage, and the spores uredosjiores, sometimes "summer 

 spores."' 



Fig. 51. 



Wheat rnst, showing the winter spores (teleutospores).- 

 H. Marshall Ward. 



Toward the end of the summer the same mycelium 

 develops sporophores which bear an entirely different kind 

 of spore (Fig. 51). It is two-celled, with a very heavy black 



