Aug. 27, 1917 Ptcccinia graminis on Cereals and Grasses 491 



.^^cia did not appear on barberries as early in 191 6 as in 191 5, owing 

 probably to the late spring. Very heavy infection of barberries with 

 P. graminis secalis was observed in Hennepin County, Minn., on May 

 26, and a few days later ascia of P. graminis tritici were found. By 

 June 15 ascia were abundant in many localities. New aecia contin- 

 ued to be developed until well into July. The unusual number of gecia 

 was very noticeable. Barberry bushes were often rendered unsightly 

 on account of the severity of rust attack. By July 5 rust was becoming 

 fairly abundant on many grasses, and a number of cases were observed 

 where various grasses were severely affected, while wheat, barley, and 

 rye near by were just beginning to develop a moderate amount of rust. 

 This was especially true of Hordeum jubaium, which, on account of its 

 habit of growth, furnishes very favorable conditions for infection. 



The above observations show that grasses, at least in Minnesota, 

 often become severly rusted near barberries in the spring or early sum- 

 mer before rust is present to any extent elsewhere. It seems quite prob- 

 able that the urediniospores may be blown considerable distances by 

 the wind and may infect other grasses and cereals. While the writers 

 do not wish to be understood as maintaining that the sequence of bar- 

 berry to grass to cereal is responsible for general rust attacks, it is not 

 at all improbable that locally this may be very important. While it is 

 true that the percentage of viable aeciospores is often low, nevertheless 

 sufficient numbers germinate to cause heavy epidemics on grasses early 

 in the season. The possibility of transfer from the grasses or from the 

 barberries directly to cereals depends, of course, on the biologic form 

 present. P. graminis tritici and P. graminis secalis are often found on 

 the same barberries; and P. graminis avenae is not uncommon. For- 

 tunately this phase of the rust problem is being attacked vigorously 

 by the Office of Cereal Investigations, United States Department of 

 Agriculture. 



SUMMARY 



(i) Puccinia graminis has been collected on about 35 species of grasses 

 in the upper Mississippi Valley, a part of the Northern Great Plains 

 region, and a small area of the Pacific Northwest. 



(2) Inoculation experiments with the rust from about 30 grasses were 

 made and the following biologic forms were isolated: Piiccinia graminis 

 tritici, P. graminis tritici compacti, P. graminis secalis, P. graminis 

 avenae, P. graminis phleipratensis , and P. graminis agrostis. 



{3) P. graminis tritici compacti was found only in the Palouse country 

 of Washington and Idaho; it occurs on club wheat and grasses which, 

 east of the Rocky Mountains, are hosts for P. graminis tritici. No ordi- 

 nary P. graminis tritici was found west of the Rocky Mountains. 



(4) More than one biologic form may occur on the same host in nature, 

 sometime* even on the same plant. In such cases it is necessary to 



