DEVELOPMENT OF PLANTS 



225 



gained in England where it was observed that the wheat fields 

 to the leeward of the barberry bushes were especially infested with 

 rust. For this reason, a law was passed early in the history of 

 Massachusetts compelling the destruction of the barberry bushes. 

 This suggestion of relationship between the cluster-cup stage of 

 the barberry and the rust of the wheat finally led to the inocu- 

 lation of wheat plants with aecidiospores and this resulted after 

 a week or more in the appearance of the characteristic rusty 

 streaks on the leaves of the wheat. 



Considerable variation characterizes these rusts, not all of them 

 having so elaborate a life history as that outlined above. One 

 of the most common species of Puccinia affecting the wheat is 

 perennial in the wheat and possibly in other grasses where it 

 produces uredospores in the spring, thus, the aecial, telial and 

 basidial stages are eliminated. In the apple rust, the uredinal 

 stage is missing. This disease produces on the leaves of various 

 members of the apple family, yellow patches in which are formed 

 tube-like cluster cups (Fig. 162, A). The aecidiospores are only 



FIG. 162. A rust, Gymnosporangium, that infests the juniper and mem- 

 bers of the apple family: A, cluster cups on leaf of thorn apple. B, 

 teleutospore stage on red cedar, juniper. 



capable of infesting the juniper, on the branches of which they 

 produce gall-like swellings (Fig. 162, B) known as cedar apples 

 16 



