ABSTRACT
This chapter discusses basic problems of the genesis of reproductive structures in species capable of nucellar and integumentary embryony. It provides a comprehensive embryological description of the phenomenon. The chapter examines differentiation of initial cells and further development of adventive embryos in terms of general biology in order to define a theoretical background of adventive embryony in flowering plants. Microsporogenesis and gametogenesis have been studied in more detail in Citrus limon, Poncirus trifoliata, Smilacina racemosa, Feronia limonia, Zygopetalum mackayi and other species. In some species, however, significant abnormalities are found during meiosis which lead either to collapse of pollen grains or to formation of diploid or aneuploid pollen grains. Some species of angiosperms possessing either adventive embryony or amphimixis can form, apart from monosporic embryo sacs, bisporic and tet-rasporic embryo sacs. Their development follows an Allium-type in Allium odorum and A. nutans and Fritillaria-type in Euphorbia dulcis.
