Parthenogenesis
The diploid egg produced in the embryo sacs during diplospory and apospory develops into an embryo without fertilization, thus maintaining the sporophytic level of chromosomes. This process of embryo development from an unfertilized egg is called parthenogenesis. The stimulus to form embryos may be pollination dependent. For example, in grasses pseudogamy operates that involves pollination stimulus while in apomictic taxa of Asteraceae and Rubiaceae no such stimulus is required. Pseudogamy has been credited with:
- Supply of male nucleus for endosperm development,
- Activation of growth of ovule and ovary, and
- Stimulation of parthenogenesis.
Pollination even otherwise is reported to initiate the development of adventive embryos of Citrus. Likewise, parthenogenetic development of embryo proceeds in apomictic grasses but normal embryos results only when endosperm is also formed.