FUNGI 



151 



Fio. 143. A cluster-cup (on barberry) of wheat-rust 

 containing chains of spring spores. After STRAS- 



BURGER. 



usually the under one, groups of sporophores, each group 

 surrounded by a cup-like structure; and hence these cup- 

 like clusters have been called cluster-cups. In these cluster- 

 cups the spores oc- 

 cur in long chains, 

 and may be called 

 spring spores or clus- 

 ter-cup spores (Fig. 

 143). 



These spring 

 spores on the bar- 

 berry leaves are 

 scattered by the 

 wind and infect 

 young wheat plants; 

 that is, germinate 

 and produce myce- 

 lia which penetrate 



them. These new mycelia later put forth the summer 

 spores, and in this way the life cycle has returned to the 

 point with which this account began. 



It will be noted that in this life-history there are four 

 kinds of spores: (1) the early spring spores, produced by a 

 simple saprophytic filament, and infecting barberry leaves; 

 (2) the spring or cluster-cup spores, produced by a mycelium 

 parasitic on the barberry, and infecting young wheat 

 plants; (3) the summer spores, produced by a mycelium 

 parasitic on wheat, and infecting other wheat plants; (4) 

 the winter spores, produced by the same mycelium, and in 

 spring producing the saprophytic filaments. In the United 

 States the barberry is not widely distributed enough to play 

 so important a part in the life-history of wheat-rust, and 

 other seed-plants have been found to be used as hosts for 

 the cluster-cup stage of certain forms of rust. It is also 

 stated that the cluster-cup stage may be omitted, in that 

 11 



