Bacteria and Fungi 



265 



to year without the intervening barberry stage. In the 

 Northern states the destruction of all barberry plants has 



FIG. 156. The white pine blister rust. The fruiting bodies on the white pine (A) 

 produce spores that infect the leaves of the gooseberry (B and C). On the gooseberry 

 leaves the fungus produces at first yellow spores that will infect other gooseberry plants, 

 and later brown spores that carry the disease back to the pine. When a pine (D) is 

 infected by the disease, the younger parts soon die (). 



been undertaken, and this work will doubtless reduce the 

 amount of infection. The hope of effectively controlling 

 wheat rust, however, probably lies in breeding new varieties 

 of wheat that are immune to the disease. 



Other rusts also live on two host plants, and because of 

 this double life and the fact that the fungus grows on the 

 inside of its host, they are very difficult to control. The rust 

 on the red cedar produces the so-called " cedar apples," the 

 spores from which infect the leaves of the apple tree and may 

 do great damage to them. Recently the blister rust of the 

 white pine has been brought to America, and it threatens to 

 destroy what remains of our white-pine forests. In this case 



