Formation of basidiocarp initials in P. cubensis occurred only when cultures were illuminated. Short durations of light (0.0025 s of xenon-arc flash) were sufficient for initiation. Light-induced initiation was saturated at a dose of 0.345 .times. 104 ergs/cm2 at 460 nm. UV and blue wavelengths of 370, 440 and 460 nm were the most effective. Green and red wavelengths greater than 510 nm were ineffective.