558 
Journal of Agricultural ‘Research 
Vol. XXIV, No. 5 
Similar results were obtained with urediniospores of P. graminis 
phleipratensis of identical origin grown simultaneously on timothy, 
Phleum pratense, and orchard grass, Dactylis glomerata L. As can readily 
be seen from experiments 7 and 8 of Tables IX and X, the spores were 
alike in length and width; the means for the urediniospores developed 
on the timothy were 23.95 ±0.12 X 16.88±0.06 /z, while the means for the 
mediniospores obtained on the orchard grass were 23.91 ±0.15 X 17.06 
±0.08 Thus the means in both cases differed only slightly. 
A//C'/^OA^^S 
Fig. 7.—Unifonnity in length of aeciospores and urediniospores of biologic 
forms of Pucdnia graminis grown on different but equally susceptible 
host plants. 
resistant hosts • 
As a rule the width of spores is more or less constant under all circum¬ 
stances. However, a reduction in both length and width as a result of 
the effect of resistant hosts was obtained in aeciospores of P. graminis 
agrostis produced on Berberis brevipaniculata Schneid. and in uredinio¬ 
spores of P. graminis avenae grown on Bromus tectorum. A reduction in 
length only occurred in the teliospores of P. graminis tritici found on 
emmer, Triticum dicoccum Schr. Figures 9 and 10 illustrate these vari¬ 
ations very distinctly. 
