ioi6 
Journal of Agricultural Research 
Vol. XXIV, No. la 
which they will develop normally. Optimum conditions are not essential 
but extremely unfavorable conditions should be avoided. 
It is important to determine whether the urediniospores of these new 
forms are really of the avenae type, as P. graminis phleipratensis (Erikss. 
and Henn.) Stak. and Piem. develops moderately well from artificial 
inoculation on some varieties of oats and may possibly occur on some in 
the field. P. graminis agrostis Erikss. also can attack some oat varieties 
weakly. These forms, however, can be distinguished easily from P. 
graminis avenae by the morphological characters of the urediniospores. 
The urediniospore characters of the new forms clearly are those of P. 
graminis avenae (<?). However, it is not yet known whether these indi¬ 
vidual forms differ appreciably from each other morphologically. 
The geographical distribution of these biologic forms of P. graminis 
avenae is not yet known definitely. The sources of 23 collections, made 
during 1921 and 1922, are given in Table II. Form I has been collected 
from Saskatchewan to Mexico, in the central part of the continent, and 
probably is widely distributed. 
Tabl® II .—Distribution of biologic forms of stem rust of oats collected during ig2i and 
ig22 
Biologic 
Form. 
Place of collection. 
Original host. 
II 
Saskatoon, Sask., Canada. 
Avena sativa L. 
Do. 
0 V 
Lloydminster, Sask., Canada. 
a V 
Weybum, Sask., Canada. 
Do. 
I,n 
II 
Zelma, Sask., Canada. 
Do. 
Presque Isle, Me. 
Do. 
1 , II 
Litchfield, Minn. 
Do. 
I, II 
I 
Rose town, Minn. 
Do. 
St. Paul, Minn. 
Do. 
II 
Redfield, S. Dak. 
Do. 
II 
Huron, S. Dak. 
Do. 
a V 
Colmar, Iowa. 
Do. 
I, II 
I 
Lafayette, Ind. 
Poa trivialis L. 
Avena sativa. 
Huntley, Ill. 
II 
Chillicothe, Mo. 
Do. 
II 
Norman, Okla. 
Dactylis glomerata L. 
Avena sativa. 
II 
Lawton, Okla. 
II 
San Marcos, Lex. 
Do. 
I, II 
1 , II 
Boeme, Tex. 
Do. 
San Antonio, Tex. 
Do. 
1 , II 
Robards, Tex. 
Do. 
1 , II 
Saltillo, Mexico. 
Do. 
IV 
Upsala, Sweden. 
Do. 
II, III 
Potchefstroom, South Africa. 
Do. 
a If not a mechanical mixture of I and II. 
Form II seems to be even more abundantly distributed than Form I in 
the central part of North America, from Saskatchewan to Mexico, and has 
been found also in Maine, as well as in South Africa. 
Forms III and IV have not yet been found in North America. It seems 
improbable that they are abundant in the northern Mississippi Valley, 
because the White Tartar (White Russian) oat is very resistant in the 
field. Furthermore, Garber {3) produced Victory X White Russian 
hybrids which were resistant to stem rust, at least in Minnesota. As these 
