CEREAL PESTS PARASITIC FUNGI 511 



early seeding or the use of an early variety may accom- 

 plish this end. 



557. Rust perpetuation without the aecidial stage. - 

 It was demonstrated by the author (1894 and 1899) that 

 the orange leaf-rust passes the winter in Kansas in the 

 uredo stage, and, therefore, has no need of the secidial 

 stage. The latter stage, in fact, is not known to occur 

 in this country. The uredo stage must also pass over 

 the interval between harvest and fall seeding on volunteer 

 wheat or wild grasses, which it is known to do. It would 

 seem, therefore, that this rust might be in some measure 

 controlled by the prevention of volunteer wheat and eradi- 

 cation of wild host plants. Such means, however, would 

 require concerted action of farmers over a wide area of 

 country, and even then might be found impracticable. 



The over-wintering of the uredo stage of the black stem- 

 rust has not been so well established, though it is thought 

 to occur on a few wild grasses, especially wild barley, even 

 as far north as southern Minnesota. Certain investiga- 

 tors believe the results of their experiments show that the 

 black stem-rust and yellow rust may be carried over in 

 the seed. These results of few experiments have not yet 

 been confirmed by others. It is well known, however, 

 that the black stem-rust continues its existence, in some 

 instances, where there is no barberry bush within 100 to 

 1000 miles, and, as before stated, the yellow rust has no 

 aecidial stage yet discovered. 



558. Rust-resistance. That certain varieties of 

 cereals are affected with rust more quickly and severely 

 than others is a fact well known to the cereal-grower. 

 Careful trials of many varieties at several points have 

 revealed striking differences in this respect. To make 

 use of these varieties, or, if they are not. otherwise good, 



