284 



COLLEGE BOTANY 



Puccinia graminis. The mycelium lives within the host, coming 

 to the surface for the production of two kinds of spores. The 

 urediniospores (or uredospores) or summer spores are borne 

 singly and are unicellular. They germinate readily and cause 

 new infections. The teliospores (or teleutospores) or winter 

 spores are borne singly and are two-celled. They germinate the 



FIG. 134. Apple rust 



following spring, producing a promycelium which bears sporidia 

 in groups of four. The sporidia correspond to the spores in the 

 Autobasidiomycetes. These sporidia germinate and are capable 

 of infecting the barberry and giving rise to the secidium or cluster 

 cup stage. The secidiospores are borne in rows in a cup-like 

 growth on the under surface of the leaf. These spores can 

 germinate and infect the wheat. On the upper surface of the 

 barberry leaf we find small flask-shaped organs known as pycni- 

 dia (or spermogonia] and bearing very small pycnospores. 



