SUMMARYThe pure culture of plasmodia ofPhysarum flavicomumin semidefined media is reported. The decline of growth of the plasmodia on the semidefined medium and the apparently inhibitory effect of certain vitamins is discussed in relation to the stimulation of growth by high concentrations of quinic acid. High concentrations of quinic and gallic acids also stimulate sporulation in pure culture. The sporangia so induced contain viable spores which readily germinate on appropriate media. The amoebae have not been induced to multiply and grow independently, but will give rise to plasmodia in the absence of multiplication. These plasmodia may be subsequently cultured to complete the life cycle in pure culture.