THE FUNGI. 



157 



CLASS V. The Rusts (JEcidiomycetes or Uredinece). 

 The Rusts are parasites which infest the tissues of higher 

 land plants. They sometimes grow in the intercellular 

 spaces, and perhaps do no injury to their host. In other 

 cases they grow in the cellular tissues, often causing great 

 deformity and injury. (See Fig. 89.) The spores are 

 produced beneath the epi- 

 dermis of the host. They 

 are somewhat of the color 

 of iron rust, and so give 

 the common name to the 

 plant. Many species of 

 Rusts produce different 

 kinds of spores, but not 

 on the same plant. There 

 is a succession in their 

 development which re- 

 quires plants of different 

 kinds. A familiar exam- 

 ple of this is the Rust 

 that causes disease in Wheat. It is known as Puccinia 

 graminis. It has different kinds of spores. One kind 

 grows on the Wheat ; the other kind on Barberry bushes. 

 In the spring cuplike yellow clusters develop on the Bar- 

 berry leaves, producing spores called cecidiospores. These 

 spores are carried by the wind to Wheat fields, where 

 they grow and produce an entirely different kind of spore, 

 called uredospores. These new spores are carried to other 

 Wheat plants and develop. This continues as long as 

 the conditions are favorable. Late in autumn spores 

 with thick coats are produced, called teleutospores. These 

 develop in the spring on Barberry leaves into cuplike 

 clusters which bear the recidiospores. 1 



1 Have on hand material collected from the different sources mentioned 

 and at the different seasons, and arrange Practical Studies. 



FIG. 89. Section of Blackberry leaf, 

 showing development of Orange rust 

 spores. (After Clinton.) 



