(A) Race tube assays with FRH mutants. Every circadian cycle N. crassa lays down aerial hyphae that appear as fluffy yellow/orange conidial bands. The distance between the bands reflects the clock period. The strains were grown in constant darkness and growth fronts were labeled every 24 h (black vertical lines), rhythmicity on right (τ= period in hours, σ = standard deviation, n = number of race tubes, ARR, arrhythmic). The race tubes shown here are representative samples from three replicate tubes. 