244 PLANT DISEASES 



appear in sufficient quantity to do any harm. Removing 

 the infected sedges will prevent its appearance. 



Klebahn, Zeitschr. f. Pflanzenkr^ vol. v. p. 76 (1895). 

 Smith, Gard. Chron.^ vol. xvi. p. 76, 1881, figs. 



GRAIN RUSTS 



Notwithstanding the combined efforts of scientists and 

 practical men in various countries to devise some method 

 for preventing the enormous amount of damage to our 

 cereals caused by fungi belonging to the genus Pucdnia, 

 the problem yet remains unsolved. Nevertheless, a large 

 amount of valuable information has been acquired, and it 

 is generally acknowledged that we are now in possession 

 of two general principles bearing on the subject : (i) that 

 from the present standpoint of knowledge, spraying with 

 fungicides is of no practical value in preventing rust; (2) 

 that the production of rust-resisting varieties of wheat 

 should be aimed at, the results of experiments already 

 accomplished in this direction being most encouraging. 



The essential points that collectively contribute to form 

 rust-proof varieties are : toughness of the epidermis of the 

 leaf; leaf narrow, fairly rigid, and erect, or nearly so. 



Early sown and early ripening varieties escape rust 

 best. 



Top-dressings of nitrate of soda (Chili saltpetre) make 

 the foliage soft and broad, and consequently more suscep- 

 tible to rust. Nitrate of soda retards ripening, and thus 

 favours rust. 



The following is from Dr. Eriksson's latest resume of his 

 researches on the grain rusts. There are at least ten kinds 

 of fungus which cause rust in cereals, partly species, partly 



