PI.ATE 2 
Photomicrograplis of uniform magnification showing the relative size and ^ape of the 
urediniospores of three biologic forms of Puccinia graminis: 
A. — P. graminis tritici. 
B. — P. graminis phleipratensis. 
C. — P. graminis agrostis. 
Photographs illustrating the effect of susceptible and resistant barberry species on the 
aecial development of biologic forms of stem rust: 
D and E.—Showing similar and normal development of cluster cups of P. .gram- 
inis secalis on two equally susceptible species, Berberis vulgaris and B. sieboldiif 
respectively. 
F and G.—Showing the difference in the aecial development of a single biologic 
form, P. graminis agrostis, when grown on susceptible and resistant barberry species, 
viz, B. vulgaris and B. brevipaniculata, respectively. 
