THALLOPHYTES : FDXGI 



67 



appear : (1) sporidia, which develop the stage on the barber- 

 ry ; (2) cecidiospores, which develop the stage on the wheat ; 

 (3) nredospores, which repeat the mycelium on the wheat ; (4) 

 teleutospores, which last through the winter, and in the spring 

 produce the stage bearing sporidia. It should be said that 

 there are other spores of this plant produced on the barberry 

 (Fig. 53), but they are too uncertain to be included here. 



The barberry is not absolutely necessary to this life cycle. 

 In many cases there is no available barberry to act as host, 

 and the sporidia germinate directly upon the young wheat, 

 forming the rust-producing mycelium, and the cluster-cup 

 stage is omitted. 



Fig. 54. Two species of "cedar apple" ( Gymnosporangium), hofh on the common 

 jnniper {Junipems Virgimana). — .1 after Farlow, B after Engler and Prantl. 



47. Other rusts. — Many rusts have life histories similar 

 to that of the wheat rust, in others one or more of the 

 stages are omitted. In very few have the stages been con- 



