TEXTBOOK OF BOTANY 



the Indian corn rust. In the case of each of these -rusts, the summer 

 stage is passed upon a cereal grain, and the spring stage, where one 

 has been found, is passed upon an entirely different plant. For ex- 

 ample, the crown rust of the oat has its spring stage on the buckthorn, 

 and the spring stage of the corn rust is found on the wood sorrel. 



100. Apple Rust. The fungus that causes this disease 

 produces its winter spores upon the red cedar (jumper), 



FIG. 31. A " cedar apple " in the spring ; the finger- 

 like projections are masses of jelly in which the winter 

 spores germinate. After Jones and Bartholomew. 



where it causes the swellings of the twigs and small branches 

 that are called " cedar apples " (Fig. 30). The cedar tree 

 is weakened if it is seriously affected, and sometimes it is 



