DISEASES OF PLANTS 



239 



Like most other fungi ; the smuts do the most damage 

 in wet weather. 



RUSTS 



Every one who is familiar with grain as it grows in the 

 field has seen the black or reddish spots on the stalks 

 which are known as rust. The red 

 spots are seen under the microscope 

 to be masses of redsjporesjyhich are 

 called the summer spores; the same 

 fungus which produces these spores 

 also produces black spores which cause 

 the black spots; these black spores 

 are called autumn, spores. They rest 

 during the winter, and in the spring 

 infect the barberry plant by means 

 of the wind, producing little reddish 

 cups on the leaves known as cluster 

 cups. The spores produced in them 

 are called cluster-cup spores. They 

 in their .turn infect the plants of grain 

 on which the summer and autumn 

 spores are again produced. If there 

 are no barberry bushes near by, the 

 summer spores may, in some cases at 

 least, live through the winter and in- 

 fect the grain in the spring. FIG. iss. 



It is probable that the rust of one Sailt 



