64 



PLANT STRUCTURES 



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

 that this completed the life cycle, and the fungus received 

 the name Uredo. When it was known that this is but one 



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

 leaf down among the nutritive cells. — After H. Marshall Ward. 



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

 stage, and the spores uredospores, sometimes "summer 

 spores." 



Fig. 51. Wheat rust, showing the winter spores (teleutospores). — After 

 n. 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 



