Aug. 27. 1917 Puccinia graminis on Cereals and Grasses 493 



tainty if the spores measured have been developed under approximately 

 similar conditions. 



(13) The rate of development of a given biologic form depends on the 

 vigor of the rust strain, the kind, and sometimes the age of the host 

 plant, the amount of light, heat, and humidity. SunUght, high relative 

 humidity, and moderate temperatures, up to about 75° F., are favorable 

 to rust development. 



(14) Preliminary observations were made on the overwintering of the 

 uredinial stage on grass hosts, but definite conclusions have not been 

 reached, except for P. graminis phleipratensis which survived the very 

 severe winter of 1916-17 at St. Paul, Minn., very easily. 



15) There is evidence to show that grasses often rust in the spring or 

 early summer before rust appears in grain fields in the same vicinity. 

 This is especially true if grasses are near barberries. The rust thus devel- 

 oped early in the season has usually been the rye and wheat stemrust 

 forms. 



(16) Inconceivably large numbers of urediniospores are produced by 

 various grasses in cereal-gromng regions. Unquestionably, therefore, 

 grasses are very important in increasing the amount of infective material 

 and in this way, if in no other, they are important in the cereal-rust 



problem. 



LITERATURE CITED 

 (i) Arthur, J. C. 



1905-08. ctn.TURES OP UREDINEAE IN 1904-07. /n Jour. Mycol., v. 11, no. 76, 

 p. 50-67, 1905; V. 12, no. 81, p. 11-27, 1906; V. 13, no. 91, p. 189-205, 

 1907; V. 14, no. 93, p. 7-26, 1908. 



(2) 



1909-10. CULTURES OP UREDINEAE IN 1908-09. In Mycologia, v. i, no. 6, 

 p. 225-256, 1909; V. 2, no. 5, p. 213-240, 1910. 



(3) BOLLEY, H. L. 



1891. WHEAT RUST: IS THE INFECTION LOCAL OR GENERAL IN ORIGIN? In 



Agr. Sci., V. 5, no. 11/12, p. 259-264. 



(4) and Pritchard, F. J. 



1906. rust PROBLEMS. FACTS, OBSERV.\TIONS AND THEORIES. POSSIBLE 



MEANS OF CONTROL. N. Dak. Agr. Exp. Sta. Bui. 68, p. 607-672, 



30 fig- 



(5) CarlETON, M. a. 



1893. notes on the occurrence and distribution op uredine^. in 

 Science, v. 22, no. 548, p. 62-63. 

 (6) 



1899. CEREAL RUSTS OF THE UNITED STATES: A PHYSIOLOGICAL INVESTIGATION. 



U. S. Dept. Agr. Div. Veg. Phys. and Path. Bui. 16, 74 p., i fig., 

 4 col. pi. Bibliography, p. 70-73. 



(7) 



1904. INVESTIGATIONS OP RUSTS. U. S. Dept. Agr. Bur. Plant. Indus. Bui. 



63, 29 p., 2 col. pi. 



Refers to statement by Arthur, p. 18, footnote. 



(8) Eriksson, Jakob 



1894. UEBER DIE SPECIALISIRUNG DES PARASITISMUS BEI DEN GETREIDEROST- 



PILZEN. In Ber. Deut. Bot. Gesell., Bd. 12, Heft 9, p. 292-331. 

 Literatur-verzeichniss, p. 330-331. 

 100305°— 17 5 



