FACTORS CONDITIONING DEVELOPMENT OF SEXUAL AND APOGAMOUS RACES OF PHASCUM CUSPIDATUM HEDW.

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Abstract
Summary: The effect of the intensity and composition of daylight and fluorescent light on vegetative growth and reproduction of the haploid sexual and diploid apogamous races of Phascum cuspidatum Hedw. has been investigated, using leaf number as an index of vegetative growth. Sown together in daylight at different seasons, both races proved to be summer annuals. In both races it was shown that leaf number is not conditioned by light intensity and that vegetative growth was prolonged in fluorescent light. The frequency of the vegetative development of sporangia in the diploid apogamous race was found to be low in daylight. Reduction in leaf number under coloured filters was not accompanied by increased development of sporangia; but under yellow‐filtered fluorescent light the frequency of sporangial development is greatly increased.The low fertility of the diploid apogamous race of this and other species is discussed, and it is proposed that alternation of generations in mosses is based in part on a mechanism which ensures that neither sporophyte nor gametophyte alone can form sporangia.

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