ABSTRACT
S. E. Williams believes that dioecy represents only a short-term reaction on outbreeding: in competition with hermaphroditic species in which the system of self-incompatibility reduces inbreeding, dioecious species should disappear or come back to hermaphroditism. The combination of heterostyly and self-incompatibility has a regular character; in this connection the heterostylous system of cross-breeding can be considered one form of self-incompatibility. Plant reproduction and propagation in different breeding systems are associated with certain energy expenditures for pollination. The breeding or recombination systems provide the equilibrium between the processes that create variability and the processes providing genotype reproduction. Three modal states of these systems are distinguished: open, limited and closed recombination systems. A relationship between flower types and type of recombination system was found in Potamogeton species. Plants with submarine flowers are autogamous forms and have low P/O, while forms with surface flowers are characterized by allogamy and high P/O, the pollen being larger.
