PLATE a 
Germination of spores of Urocystis tritici . 
All figures were photographed with 4-mm. objective and No. 10 ocular by Miss Ruth 
Colvin, Office of Fruit-Disease Investigations, Bureau of Plant Industry, United 
States Department of Agriculture. 
A. —Spore balls, each with one or two spores, invested by sterile cells. 
B. —Germinating spore with promycelium. 
C. —Germinating spore with sporidia just forming at apex of promycelium. 
D-E.—Germinating spores with sporidia. 
F. —Sporidia elongating, forming the so-called infection threads (a). Two sporidia 
( b ) did not elongate. 
G. —Spore ball with two spores germinating, each with sporidia at the apex of the 
promycelium. 
H. —Spore ball with four spores in different stages of germination; (a) sporidia be¬ 
ginning to elongate, ( b ) sporidia just forming, (c) sporidia formed, and (d) sporidium 
elongated to form an infection thread. 
I. —Three sporidia, each with a secondary sporidium. 
