DISEASES OF WHEAT 



163 



of spores characteristic of the different stages in the life cycle 

 of such a fungus are so different in form and character and so 

 divergent in their modes of development and subsequent habits 

 of growth as to mislead the investigator completely and excite 

 no idea of relationship. Several entirely different types of hosts 

 are frequently utilized in the life cycle. It is because of their 

 complex life history that rusts have so long been shrouded in 

 mystery and confusion, and inadequately understood. 1 



The wheat rusts produce in order, from spring to spring, four 

 different forms of spores. (1) Aecidiospores (injuring spores) 

 are the first spores found in the year. They occur on shrubs, 

 or herbs other than grasses. (2) Uredospores (blight spores) 

 appear in the early summer, and are often called summer spores. 



TWO FORMS OF RUST SPORES COMMONLY FOUND ON WHEAT 



At the left is shown the uredospores of the red rust, commonly found in early 

 summer. At the right, the two-celled teleutospores or winter spores of the 

 black rust. 



These are the red spores that rust the leaf of the wheat. (3) 

 Teleutospores (completion spores) are the last ones of the sea- 

 son. They are also known as resting or winter spores. Their 

 dark color gave rise to the term " black rust." (4) Sporidia 

 are very minute and delicate spore bodies formed in the spring 

 on the germination tubes of the winter spores. The sporidia 

 infect the plant that is host to the aBcidium stage. The 

 question of a breeding act in the rust life cycle is still an un- 

 settled one. 



When the a3cidiospore lodges upon the wheat leaf or stalk 

 in the spring, it remains in a resting condition until a light 



1 The works of Bolley, Carleton and Freeman will be found 

 most useful in a study of rusts. 



