Abstract
The following facts suggest that monoecism is an advanced condition derived from dioecism in the evolutionary history of bryophytes. 1. In many species, the strain with a haploid chromosome number is dioicous, while the diploid one is monoicous. 2. Monoicous species sometimes show limited distribution in spite of their high frequency of fruiting, which is seen, for example, in members of Hypnum. 3. Bryophytes growing on trunks, decayed wood or living leaves of vascular plants include many species of monoicous sexuality. 4. Species with small gametophytes are apt to be monoicous ; examples are given by the genera Fissidens, Thuidium and Hypnum. 5. Most annual bryophytes, which are usually nitrophilous, are monoicous. Species of the families Ephemeraceae, Funariaceae and Splachnaceae are examples. 6. The Marchantiales, which show more differentiated thalloid structure, and the Anthocerotae, which are, in the progressive theory of evolution, considered to be most highly advanced, include many monoicous species. 7. Monoicous species have several functions to prevent self-fertilization, and have possibly evolved by outbreeding.
