116 



THE CEREAL RUSTS. 

 W. P. Eraser, Biology Department, Macdonald College. 



The rusts are a large group of fungi which are parasitic on flowering 

 plants and ferns. The vegetative part of the fungus consists of threads 

 which grow in the tissues of the plants and send branches called haustoria 

 into the cells by means of which the fungus obtains nourishment. The 

 plant at the expense of which the fungus lives is called the host. As the 

 mycelium lives in the tissues of the plant it is inconspicuous, but after 

 a time spores are produced which usually break through the epidermis 

 and appear as powdery or compact masses or crusts. Spores of five kinds 

 may be produced, though they may not all be present in every species. 

 These spores always follow one another in definite order. The first to 

 appear are the spermatia which as far as is known have no function and 

 take no part in the development or spread of the fungus. Spring spores 

 or aecidiospores are produced next, followed later by summer spores -called 

 uredospores. Finally the teleutospores or winter spores are produced, 

 which usually serve to carry the fungus over the winter, but in some species 

 this is not the function of the teleutospore. Under certain conditions 

 which vary in the different genera and species the teleutospores send 

 out tubes and on these secondary spores called sporidia or basidiospores 

 are produced. These, if they reach a suitable host plant start the fungus 

 again in the spring. One or more of the spore forms may be absent in 

 certain genera or speqjes, but the spore succession is always the same. 



Many rusts pass part of their life cycle on one plant and part on another, 

 and usually these plants are not closely related botanically. When 

 this is the case the spermatia and aecidiospores are produced in one host 

 and the uredospores and teleutospores on the second. The cereal rusts 

 belong to this two host group of rusts, though the complete life cycle of 

 some species is not known. 



The Stem Rust of Grains, {Puccinia graminis). This is the best 

 known of the cereal rusts. It attacks wheat, oats, rye, barley and many 

 grasses and is more or less common wherever these are grown. 



The complete life cycle of the stem rust is as follows. In the spring 

 the winter spores or teleutospores that have been exposed to the weather 

 during the winter germinate by sending out a tube from each cell called 

 a basidium and in this four secondary spores, the sporidia, are produced. 

 These spores are carried by the wind and if they reach the barberry (Ber- 



