Minnesota Plant Life. 



53 



rieties. While smut is, upon the whole, the easiest of the wheat- 

 diseases to control, rust is the most difficult. 



The remarkable migratory habit of the wheat-rust and its 

 allies coupled with the extraordinary change in form which the 

 fungus assumes upon the different habitats gives rise to some 

 very surprising conditions in rust life-histories. For after the 

 migratory habit had been formed it would appear that some- 

 times one or the other of the phases became extinct, so there 

 are varieties of rusts which exist only in the cluster-cup phase, 



FIG. 14. Magnified section through a cluster-cup of the wheat-rust in its barberry-leaf stage. 

 Shows chains of spore-cells. The large cells at the sides are those of the barberry leaf 

 much magnified. After Atkinson. 



and others only in the red and black-rust phases. For a long 

 time students of the fungi thought that the cluster-cups were 

 entirely different from the rust, and it was only because people 

 noticed more than a century ago that "barberry bushes," as the 

 saying was, "blasted the wheat," that a hint was given to mod^ 

 ern research, in consequence of which the astonishing behavior 

 of the rust fungi is now more thoroughly understood. 



Relatives of the wheat-rust. Among the relatives of the 

 wheat-rust there are some forms in Minnesota characterized by 

 little peculiarities which enable botanists to classify them in dif- 

 ferent genera. For example, the black-rust spores formed on 



