Observations and Experiments on Cereal Rusis. 169 
Carleton* has however stated that rye and species of Agro- 
pyron are not infected by this form. Again Jaczewskif says 
that barley and Lolium perenne can be infected, but rye, oats 
and Dactylis glomerata are immune. Lastly Butler and Hayman} 
have also found that in India this form can infect barley. 
This form has not been found in the locality under report on 
any other host except wheat. It will be clear from the above 
results that the specialization of this form is quite rigid and that 
among the cereals it infects only wheat (its original host) and 
barley. The capability to infect wild grasses is doubtful on 
account of the small number of trials made. 
Amongst the varieties of wheat tried Red Sudan is exceed- 
ingly susceptible to this rust. Other varieties, Burbanks, 
Wilhelmina, Little Joss, Yeomen, Dreadnought, are all mode- 
rately susceptible. Squareheads master and American club are 
only weakly infected but Einkorn wheat is very highly re- 
sistant, though not altogether immune. 
Amongst the varieties of barley tested, Bg, (the Mesopotamian 
variety exceedingly susceptible to yellow rust) has been found 
to be far more susceptible than 5,, 6,; or Bg,. In order to find 
out if barley was a “‘bridging host” for this form seedlings of 
rye, oats, barley and Red Sudan wheat were inoculated with 
the material cultivated on barley (B39). It is interesting to note 
that wheat (the original host) and barley were infected but rye 
and oats were not. 
In February and March 1922 the writer inoculated on two 
different occasions seedlings of wheat, barley, rye and oats with 
uredospores of this form after their cultivation on Red Sudan 
wheat (exceedingly susceptible) for thirteen and fourteen genera- 
tions respectively. Wheat and barley became infected but rye 
and oats were quite immune. 
The writer is in complete agreement with Stakman, Piemeisel 
and Levine§ and Stakman, Parker and Piemeisel|| who have 
stated that the pathogenicity of biologic forms is not changed 
by bridging hosts or by association with a given host. The form 
under discussion did not acquire any new parasitic capability even 
after its continuous cultivation for over sixteen months on Red 
Sudan wheat. Puttick has also pointed-out that the parasitic 
* Carleton, M. A., U.S. Dept. Agric. Div. Veg. Phys. and Path. Bull. No. 16 
(1899). 
t Jaczewski, A. A., Zeitschr. f. Planzenkrankh. xx, p. 321 (1910). 
{ Butler, E. J. and Hayman, J. M., Mem. Dept. Agric. India, Bot. Ser. i, 
No. 2 (1906). 
§ Stakman, E. C., Piemeisel, F. J. and Levine, M. ‘N., Journ. Agr. Res. xv, 
p- 221 (1918). 
|| Stakman, E. C., Parker, J. H. and Piemeisel, F. J., Journ. Agr. Res. xiv, 
p- I1z (1918). 
| Puttick, G. F., Phytopathology, x1, p. 205 (1921). 
