Relation of Rusts to other Fungi. 41 



plants for their sustenance, they must accommodate themselves to their 

 surroundings, and so they may pass through different stages, sometimes on 

 the same plant, or on different plants. These various stages represented 

 by different reproductive bodies, enable the rust to produce spores which 

 can germinate at once if food supplies are available, or others which can 

 rest if need be. The change of host is an evident advantage, not only 

 from the point of view of a change of diet, but it may thus pass from one 

 plant that dies down to another that is perennial. It may even become 

 perennial itself in the underground parts of some plants, and then it 

 vegetates, only producing rarely the reproductive bodies which would 

 be formed under normal conditions. 



