Influence of Varying Periods of Light and Dark on Asexual Reproduction of Pilobolus kleinii

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Abstract
P. kleinii was grown in pure culture on a dung-decoction agar. A periodicity in the development of the asexual fruiting body (sporangiophores mature at the end of a dark period (D) and immature at the end of a light period (L)) was established under certain alternating periods of light and darkness of equal and unequal duration. Periodicity was displayed under the 12(D)-12(L) (hrs.), 16-16, 15-9 and 9-15 cycles. No periodicity was noted under continuous light and in total darkness, and also under 4-4, 8-8, 24-24, 4-20 and 20-4 cycles. It would appear that, although light is necessary for the continued growth and maturation of the fruiting body, a certain period of darkness is necessary to establish a periodicity of growth and maturation. When periodicity was displayed by the fungus (16-16), the periodic effect was quite consistent day after day. Thus it would appear that once a pattern of growth and maturation has been established by the fungus in response to a light-dark cycle other than that found in nature, the fungus continues to respond to that cycle in a consistent manner. Under the conditions imposed by the different light-dark cycles, some morph. variations of the normal growth habit were found. Constancy in the type of variation was noted under specific cycles.