Abstract
Zonation in cultures of Fusaria was found to occur from the influence of light or temperature. An exposure of Fusarium discolor sulphureum to bright daylight for one-fourth to one-half second is sufficient to produce a ring of conidia which can be detected by the naked eye. A six-minute exposure to the light from a 25 candlepower carbon lamp at one meter distance was required to produce a noticeable ring, but an exposure of 2 to 2¼ minutes to a tungsten-filament lamp of about the same candlepower sufficed to induce the zone-formation. The light acts upon the outermost tips of the hyphae, and the phenomenon is, at least in part, another case of the effect of light upon growth. Zonation may also be induced by alternating temperature in constant darkness.

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