444 
Pole Evans . — The Cereal Rusts . 
that each set of phenomena is of a very definite nature for each species of 
Uredo, i. e. the infection phenomena presented by Uredo graminis on 
wheat is always of the same definite type and differs markedly from say 
Uredo triticma on wheat or any of the other Uredo forms to be described, 
which again in their turn are all constant. In uredospore infection it is 
usual to recognize two distinct steps : entry or inoculation and true 
infection. 
In addition to the preliminary act of germination, entry or inocula- 
tion includes the swelling up of the tip of the germ-tube over the stoma, 
to form the appressorium. From the appressorium a slender branch 
passes through the stomatal slit and at once swells out into a vesicular 
body, the substomatal vesicle, into which the whole contents of the 
spore is poured. The entry of the fungus is now assured. 
The next step in the development is the putting forth from the 
substomatal vesicle of one or more infecting hyphae, which closely apply 
themselves to the host-cells and send in their haustoria, thus bringing 
about the act of infection. 
Puccinia graminis Tritici , Erikss. and Henn. 
The Black Rust of Cereals, which is heteroecious on Barberry, has 
been broken up by Eriksson (12) into six specialized forms : — 
1. Puccinia graminis Secalis , found on Sec ale cere ale, Hordeum vulgare, 
Agropyrum repens , Elymus arenarius , and Hordeum comosum, but not on 
Triticum vulgar e or Avena sativa. 
2. Puccinia graminis Tritici on Triticum vulgare. He regards this 
form as ‘ not sharply fixed because he says Uredo infection from Wheat 
feebly infects Barley, Rye very slightly, and in the case of Oats he regards 
the infection as doubtful. 
3. Puccinia graminis Avenae on Avena sativa, Alopecurus pratensis , 
Dactylis glomerata , but not on Triticum vulgare , Hordeum vulgare , or 
Secale cere ale. 
4. Puccinia graminis Airae on Air a caespitosa only. 
5. Puccinia graminis Agrostis on Agrostis canina and A. stolonifera 
only. 
6. Puccinia graminis Poae on Poa only. 
In this paper we shall concern ourselves solely with the form Uredo 
graminis Tritici , Erikss. and Henn., found on Wheat. 
This rust, formerly so common in England, now appears to have been 
replaced by the Yellow Rust of Wheat, Uredo glumarum, which is par- 
ticularly abundant in the Fen District. 
Uredo graminis is the rust responsible for the damage wrought in the 
Cereal crops of the United States of America, Australia, and Tasmania. 
In India, according to Barclay (3), it is comparatively unimportant. 
