CEREALS 325 



spores are to multiply and spread infection, especially in 

 the earliest part of the season. The uredospores are to 

 continue the multiplication and infection throughout the 

 growing season of the host. The last two forms of spores 

 are in general comparatively short-lived. If the host plant 

 remains alive over winter, as is the case with winter wheat, 

 the fungus, south of the fortieth parallel, may continue 

 to grow and produce summer spores all winter, and the need 

 of the other two forms is lessened. Even in colder climates 

 the uredospores of some rusts live over winter and start in- 

 fection in the spring. 



In the case of some rusts these three forms are all present 

 and are known to man. In the case of other rusts one 

 stage or even two stages may be either unknown or may 

 not exist at all. When all three stages do exist, the spring 

 stage is often upon some host other than that bearing the 

 uredo and teleuto stages. Thus the spring stage of the 

 wheat rust is upon the barberry; of corn upon oxalis; 

 of oats upon buckthorn. 



That some intimate relation existed between the bar- 

 berry bush and the wheat rust was believed very early 

 in the eighteenth century, and in 1760 Massachusetts 

 passed a law placing a ban upon the barberry. In 1818 

 Schroeter, a Danish school-teacher, published many obser- 

 vations concerning the relation of the cluster cup upon the 

 barberry and the rust of grains. This relation was finally 

 definitely proved by DeBary in 1864, who, by sowing the 

 teleutospores from the wheat upon the barberry, produced 

 the cluster cups. 



All cereal rusts multiply much more rapidly in damp 

 than in dry weather, and the most destructive rusts are 



