Observations and Experiments on Cereal Rusts. I7I 
_ Again Stakman and Piemeisel* in the United States have 
stated that this form is found on Agrvopyron repens, Hordeum 
jubatum, barley, rye and some other hosts in the field. The 
same authors succeeded in infecting barley easily but not 
Dactylis glomerata, Lolium perenne and Arrhenatherum avena- 
ceum, etc. As regards wheat these authors have remarked that 
it is very rarely or scarcely at all infected by this form. Out of 
four hundred and fifty-four trials according to their data only 
three gave positive results. These authors state that oats also 
can be rarely and weakly infected. 
It will be seen that it has been possible to infect Agropyron 
vepens (the original host), rye, barley and contrary to what has 
been reported from other regions, even wheat (at least the 
variety Red Sudan). Oats are not infected. About the grasses 
mentioned above the writer is doubtful (on account of the small 
number of trials) if they can be infected by this form. 
As regards Red Sudan (wheat) infected by this form positive 
results were obtained in twenty-nine cases out of fifty with un- 
doubtedly a pure culture (after cultivation on rye for twelve 
generations). The size of the uredo-sori developed on wheat 
was invariably much smaller than those on rye or barley. 
Inoculations with material as many as ten and eleven gene- 
rations old was also tried on other varieties of wheat—Little 
Joss, Burbanks, Yeomen, Dreadnoughts, Squareheads master, 
American Club and Red Sudan and rye (as controls). Only rye 
and Red Sudan became infected and all other varieties of wheat 
were found to be immune. This fact can easily be explained on 
account of the exceedingly susceptible nature of Red Sudan. 
From over 50 % cases of successful infection one cannot but 
conclude that the specialization of this form is not absolutely rigid 
as far as wheat is concerned. It is not possible at this stage to 
make any definite statement on the possibility of wheat taking 
infection from Couch grass or rye in the open. As far as barley 
is concerned there is not the slightest doubt that Couch grass, 
on account of its plentiful distribution, may not only be re- 
sponsible for the spread, but on account of its proximity to 
barberry may even be the cause of the fresh outbreak of black 
rust on that cereal. : 
As shown in Table, p. 170, the variety most susceptible to this 
form is Bg, (Mesopotamian barley). The other varieties are not so 
susceptible. It is interesting to note that the same varieties are 
only moderately susceptible to the black rust of wheat also. 
This form too was cultivated on barley (B,,) for two genera- 
tions and inoculations were made on rye, barley, Red Sudan 
and oats with that material. Rye, barley and Red Sudan were 
* Stakman, E. C. and Piemeisel, F. J., Journ. Agr. Res. x, p. 429 (1917). 
