Observations and Experiments on Cereal Rusts. 167 
FARK! If. 
SPECIALIZATION OF PARASITISM. 
In recent years considerable work has been done on the 
biologic forms of rusts on cereals. In Europe Eriksson*, 
Eriksson and Henning} and Jaczewskit have made extensive 
investigations. In the United States Carleton§, Freeman and 
Johnson||, Pritchard] and quite recently Stakman and Pie- 
meisel** have worked on different aspects of the question. 
On account of the absence of any definite information on the 
subject for this country, and also on account of the bearing it 
has on the problem of the annual origin of rusts on wheat it 
was desirable that some investigations should be made. Further 
it is clear that in spite of the general agreement in the results 
obtained by various investigators there are interesting differ- 
ences which have indicated the necessity for such work in 
different regions. 
The present note deals with an account of some of the ex- 
periments conducted with the uredospores of black, brown and 
yellow rusts obtained on wheat in this locality. It also gives 
an account of some work done with the black rusts of barley 
and Couch grass (Agropyron repens) and the brown and yellow 
rusts of barley. 
In order to avoid the use of impure material in the experi- 
ments a pure culture was invariably first established. Inocula- 
tions with different biologic forms were made in separate 
greenhouses. 
Black rust from wheat (P. graminis tritici). 
This biologic form was observed on tillers and self-sown plants 
of wheat on the Little Joss plot in October 1920 about a couple 
of months after harvest. It was established on wheat in Novem- 
ber and since then its culture has been kept in the laboratory. 
The following is the table of results of inoculations with that 
material after its culture on wheat for six generations. In 
experiments (2) and (3) material used was respectively twelve 
* Eriksson, J., Ark. f. Bot. 1, p. 139 (1903); Ber. Deutsch. Bot. Gesell. x11, 
Pp. 292 (1894); Centralbl. f. Bakt. Bd. rx, Abt. 2, p. 590 (1902); Zeitschr. f. 
Pflanzenkrankh. Iv, p. 66 (1894). 
{ Eriksson, J. and Henning, E., Die Getreideroste (1896). 
{ Jaczewski, A. A., Zeitschr. f. Pflanzenkrankh. xx, p. 321 (1910), 
§ Carleton, M. A., U.S. Dept. Agric. Div. Veg. Phys. and Path. Bull. No. 16 
(1899) 
|| Freeman, E. M. and Johnson, E. C., U.S. Dept. Agr. Bur. Plant. Indus. 
Bull. p. 216 (1911). 
| Pritchard, F. J., Bot. Gaz. Lu, p. 169 (1911). 
** Stakman, E. C. and Piemeisel, F. J., Journ. Agr. Res. x, p. 429 (1917). 
