As Mnium undulatum was shown to be homosporous, it was concluded that neither male nor female derived an advantage from spore size that might be related to the observed excess of female plants. The rate of germination was greater at 20 °C than at 10 °C in M. hornum and M. undulatum, and was also reduced in short days (7.25 hours) at both temperatures. Spores of M. undulatum germinated more slowly than those of M. hornum under each of the environmental regimes used. Isolated spores of M. undulatum showed a ratio of 1♂: 4.1♀ compared with 1♂: 0.89♀ in M. hornum. The excess of female plants of M. undulatum that had been established by the end of germination, was maintained amongst the first protonemal buds produced (1♂: 3.5♀), whereas an excess of male M. hornum was observed in the first protonemal buds (1♂: 0.45♀). Frost reduced the rate of germination in M. undulatum, but unlike desiccation did not affect the final percentage. Male and female were amongst the spores which survived desiccation at 10 °C. Regeneration of detached leaves occurred more rapidly in M. undulatum than in M. hornum, and no difference between male and female was detected. It was found that frost prior to or during regeneration did not produce long-term harmful effects in M. undulatum. None of the young male gametophytes produced by regeneration from leaves survived desiccation, compared with 77 per cent of similarly produced female gametophytes.
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Martha E. Newton (1972) studied this question.