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Figure 11.9 Rate of spore discharge from cultures of Sordaria fimicola under alternating conditions of light (unshaded area) and dark (shaded area). Cultures were grown in continuous light until day 12, and then light periods were made to correspond with "natural" period of maximum discharge for three days. The phasing of the light periods was then shifted through 12 hours by imposing either a 24 hour-period of light (a) or darkness (b). Spore discharge was immediately entrained to the new light phase. (From Austin (1968). With permission of the publisher.)

enough to rephase sporangiophore development (Bruce et al., 1960). In Sordaria fimicola (Ascomycotina) grown in plate cultures under alternating conditions of 12 hours of light and 12 hours of darkness, the discharge of ascospores occurred 6 hours after the beginning of the light period (Austin, 1968). The phasing of the light period was then shifted through 12 hours by imposing either a 24-hour period of light or darkness (Figure 11.9). Spore discharge was immediately entrained to the new light phase. The fact that circadian rhythms can be entrained demonstrates they are adaptive. The biochemical mechanism of adjustments remains a mystery.

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