CHAPTER IV 



LIFE-HISTORIES OF OTHER UREDINALES 



Puccinia graminis. 



The Black Rust or " Mildew " of Corn. 



Another common Puccinia, whose life-history is of greater 

 economic importance than that of P. Caricis, is the well known 

 P. graminis, the Rust or Mildew of Corn. This species has its 

 spermogones and gecidia on Barberry (Berberis vulgaris and 

 Mahonia Aquifolium) and its uredo- and teleutospores on many 

 species of grasses, especially on cultivated wheat. It must not, 

 however, be assumed that any rust found on wheat is P. gra- 

 minis ; there are at least two other species common on the 

 same host which, unless carefully examined, may be confounded 

 with it, viz. P. triticina and P. glumarum, not to mention a form 

 of P. coronata which sometimes also occurs on cereals. For 

 this reason these four species are now distinguished as the 

 Black Rust, Brown or Orange Rust, Yellow Rust, and Crown 

 Rust of corn, respectively. The uredo-stage of P. graminis is 

 known as Red Rust. 



If one merely substitutes Barberry for Nettle and Wheat 

 for Carex, what has been said about P. Caricis is true in all 

 essentials of P. graminis. The differences are not in the life- 

 history, but in certain minor details of occurrence : e.g. the 

 spots caused on the leaves of Barberry are small, round and 

 red, while uredospores of P. graminis are most common on the 

 leaves, and the teleutospores form long black striae on the 



