274 GENEKAL BOTANY 



RUSTS AND SMUTS 



The rusts and smuts are the most distant relatives of the 

 mushrooms, puffballs, and bracket fungi. The relationship is 

 established largely through their method of producing spores, 

 but the evidence is too detailed for our present discussion. 

 They are of great importance in agriculture on account of the 

 destruction which they cause to the various species of cereals 

 which form the staple crops. 



RUSTS (PUCCINIA G-RAMINIS) 



This rust is heteroecious, producing four different kinds of spores 

 at different seasons of the year and in using two plant species 

 as hosts for the growth and formation of its spores. Each kind 

 of spore also plays a particular rc>le in the life history of the 

 organism (Fig. 153). 



The spring crop of spores, called ceciospores or ceeidiovpore*, are 

 borne in open cups (F) on the leaves of the common barberry. 

 These barberry spores are supported by a mycelium which pene- 

 trates the barberry leaf as a parasite and absorbs food for itself 

 and the spore-bearing hyphse produced within the barberry cups. 

 These spring spores become mature at about the time when the 

 young wheat plants are springing up in the fields, and when they 

 are blown by the wind and fall upon a young wheat plant they 

 germinate and produce a dense mycelium within the tissues of its 

 growing leaves and stem. This inner parasitic mycelium then 

 forms red-rust spores, in groups called sori (-5), at certain points 

 along the surface of the leaves and the stem. These masses of 

 spores break through the epidermis and form the long lines of 

 spores (J[) familiarly known as red rust. 



These summer spores, called urediniospores or uredospores, are 

 single-celled and are borne on a short stalk. They are quickly 

 disseminated, and since they germinate at once under favorable 

 conditions, they serve to spread the rust very widely in the fields 

 of grain in early summer. In warm regions the red-rust spores 

 often survive the winter and start the rust in the spring. 



