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SUMMARY
Urediospores of Hyalopsora polypodii collected from Cystopteris fragilis do not require a resting period prior to germination. Vesicles, appressoria, or fusion bodies do not develop within the host nor upon a nutrient agar. Perennial mycelium is absent. Infection is initiated in the spring by urediospores which have overwintered on dead fronds. Teliospores are rarely, if ever, produced in Iowa. Hyalopsora polypodii seems to be propagated solely by urediospores.