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 four 

 different kinds of 

 spores ; although 



not all the rusts 

 FIG. 26. A, the upper surface of a barberry 



leaf, showing the diseased areas caused by the rust ; act ually do bear 



the dark dots represent the openings into the cavities SO many. Many 



in which spermatia are formed. B, the lower sur- rug^g require two 



face of a leaf, showing infected areas and the cluster t 



cups 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. 



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