THE RUSTS 235 



succeeding one another, and is found upon both red and 

 white clovers. It is a widespread disease, but seldom does 

 serious injury. 



Another closely related fungus is Alfalfa Rust, but this 

 as a rule causes only a minor injury. The pustules showing 

 the summer spores are likely to be found upon alf alf a leaves 

 at any time in summer. 



The Rose Rust is still another species having a life story 

 similar to that of the Asparagus Rust. It is very frequently 

 found upon the leaves and stems of roses. Other rusts 

 occasionally occur upon beans and beets. 



WHEAT STEM RUST 



The Asparagus Rust is typical of the rusts that pass their 

 various stages upon one host. There are many others, how- 

 ever, in which the fungus develops part of the year upon 

 another host, so that the life history may seem even more 

 complex than that of the Asparagus Rust. 



The Stem Rust of Wheat is a good example of a rust that 

 lives upon two hosts. Most people in regions where wheat 

 is grown are familiar with the slender black spots on the 

 leaves and stems of ripened wheat. Under a lens these are 

 readily seen to consist of teleutospores, similar to the teleu- 

 tospores of the Asparagus Rust. They serve as the winter 

 spores of the Wheat Stem Rust, living through the winter 

 wherever the straws may be. 



In spring the teleutospores germinate by sending out 

 tubes, and these tubes in turn give rise to secondary spores 

 called sporidia exactly as in the case of the Asparagus Rust. 



These sporidia are blown about by the wind. If one 

 chances to light upon a moist barberry leaf, it germinates 

 and sends its fungus thread through a breathing pore into 



