PLATE 6 
Pyrenophora tritici-repentis 
A.—-Perithecium of Pyrenophora tritici-repentis collected on decaying leaves of 
Agropyron repens near Madison, Wis., early in April, 1919, showing well-defined 
ostiolar beak bearing a number of setae at the tip; the latter being more or less curved, 
often several times septate, occasionally branching, and tapering perceptibly from 
base to distal end. X 175- 
Ba-b.—Portions of old stem of Agropyron repens, showing numerous erumpent 
perithecia appearing on denuded stalk (Ba); and less numerous perithecia on leaf 
sheath (Bb). X S- 
C.—Ascus freshly dissected from perithecium before undergoing swelling prelim¬ 
inary to spore discharge. X 500. 
Da-b.—^Ascospores germinating by produetion of germ tubes from the greater 
number of their segments; showing also the enveloping gelatinous layer. X 500. 
Ea-d.—Ascospores showing variation in size and septation, as well as presence and 
absence of enveloping gelatinous layer. X 500- 
