Meetings of the Royal Botanical Society of the Netherlands
Acta botanica neerlandica , Volume 31 - Issue 1/2 p. 137- 145
Apomixis is often considered to be synonymous with asexual reproduction as opposed to sexual reproduction which is then called amphimixis. It occurs in two forms, viz., as vegetative reproduction (by menas of rhizomes, stolones, bulb clusters, etc.), and as agamospermy, i.e., the production of seed by means of an asexual process. Agamospermy has a strong influence on the evolution, taxonomy and ecology of certain taxa. Life cycles of agamospermous taxa belong principally to one of the following categories; (1) Diplospory, i.e.. a normal meiosis I sets in but is not completed and univalents are formed which come together in one so-called restitution nucleus which is diploid; the second meiotic division takes place normally, after that a seemingly normal embryo sac (e.s.) with 8 nuclei is formed, but its nuclei are diploid. The egg cell develops parthenogenetically into an embryo and the tetraploid secondary e.s. nucleus produces the endosperm (Hieracium subgen. Euhieracium, Taraxacum, Calamagrostis). (2) Apospory, i.e.. the meiotic divisions are usually normal, but subsequently a vegetative cell of the nucellus develops into an aposporic embryo sac cell (e.s.c.) which is diploid and ousts the legitimate e.s.c. which degenerates.In the aposporic e.s.c. 8 diploid nuclei are formed, one of which (a “diploid egg cell") forms the embryo parthenogenetically, and the secondary e.s.n, the tetraploid endosperm (Hieracium subgen. Pilosella, Crepis).
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