Abstract
Light initiated fruit‐body primordia of Coprinus congregatus Bull, ex Fr. were subjected to different dark periods (4 h to 24 h) and exposed to short blue light pulses at different times. The light break inhibited the development of primordia as did continuous light. The time of maximum sensitivity to a light break was dependent on the duration of the dark period. A short light break imposed two‐thirds of the way through the dark period produced strong inhibition of fruiting. The higher the temperature during the dark period, the lower the irradiance required for 50% inhibition of fruiting at the time of maximal sensitivity. During a very long dark period (48 h) a light break was no longer inhibitory. The light break fulfilled the light requirement for normal morphogenesis and defined the time the fruit‐bodies sporulated.