262 



THE FUNGI 



Curious structures called spermogoma (Fig. 232, C) frequently 

 accompany the cluster cups and are believed to be the remains 

 of male sexual organs now no longer functional. They develop 

 immense numbers of minute cells, termed spermatia, which may 

 at one time have been functional sperms, but apparently serve 

 no useful purpose now. 



The secidiospores are distributed by the wind and germinate 

 upon young wheat, putting forth tubes which enter the host 



FIG. 232. Cluster cups (aecidia) on barberry leaves 



A, habit sketch showing groups of cluster cups on a leaf; B, a group enlarged; 

 C, section through a leaf showing cluster cups on the lower surface, with the 

 chains of aecidiospores and the male organs (spermogonia) on the upper sur- 

 face. The latter develop immense numbers of minute cells which probably 

 represent sperms, but are now functionless 



through the stomata. The infected wheat then develops a 

 number of crops of one-celled summer spores called uredo- 

 spores (Fig. 233). The first crops of summer spores are widely 

 scattered in high winds and infect more wheat, thus spreading 

 the disease very rapidly. The spots of uredospores are reddish 

 or yellowish, and this is the stage known as the red rust of 

 wheat. Finally, at the end of the season, the black spots of 

 teleutospores appear, and the rust's life history is completed. 



