Further Observations on Light and Spore Discharge in Certain Pyrenomycetes

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Abstract
A ‘spore-clock’ for studying the hourly rate of spore discharge over a 24-hour period is described. A number of the experiments reported in this paper have involved the use of this apparatus. In Sordaria fimicola there is a distinct positive light-discharge reaction in a dark-conditioned culture, the rate of spore discharge increasing steeply to a peak 2–3 hours after brief stimulation by bright light. Although darkening a light-conditioned culture leads to an immediate decrease in the rate of discharge, there is no evidence of a delayed negative dark-discharge reaction. In S. verruculosa with a 12-hours light: 12-hours dark daily reëgime, more spores are discharged in the dark than in the light periods if the intensity of illumination is low. With higher light intensity there is no significant difference between the number of spores discharged in light and dark periods. As in S. fimicola there is a positive light-discharge reaction, the interval between stimulus and maximum response being much longer (8–12 hours). When a dark-conditioned culture is transferred to light for 48 hours and then returned to darkness for a further 48 hours it is apparent that not only is there a positive light-discharge reaction but also a negative dark-discharge response. The ‘plateau’ level of discharge is essentially the same in light and darkness. It is confirmed that in Hypoxylon fuscum light inhibits discharge.

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