CHAPTER VII 



THE WHEAT RUST 



88. The Rusts. — There is a very large group of par- 

 asitic fungi which cause great damage to the plants on 

 which they live. Growing inside the tissues of its host plant, a 



rust forms masses 

 of spores which 

 break through the 

 epidermis of the 

 host. But in- 

 stead of forming 

 only one kind of 

 spore, as the 

 bread mold does, 

 a single species of 

 ru st may bear /owr 

 different kinds of 

 spores ; although 

 not all the rusts 

 actually do bear 

 so many. Many 

 rusts require two 

 hosts, in each of 

 which a part of 

 the life history of the parasite is passed. The common 

 wheat rust, which we are to study, is one that lives for part 

 of the year upon one host, and then transfers its activities 

 to a second victim. 



60 



Fig. 26. — A, the upper surface of a barberry- 

 leaf, showing the diseased areas caused l^y the rust ; 

 the darlc dots represent the openings into the cavities 

 in which spermatia are formed. B, the lower sur- 

 face of a leaf, showing infected areas and the cluster 

 cups. 



