ABSTRACT
Ultrastructural studies on generative cell protoplasts of apomictic plants are few in number and deal with adventive embryony, and in part with apospory. It is important to clarify also whether protoplast transformations can take place during the formation of a new individual without fertilization. It is believed that adventive embryony and gametophytic apomixis are not fundamentally different types of agamospermy. The present classification is based on two principles: the nucellus is treated as megasporangium whose cells are potentially generative and have specific features in differentiation during the transition to development of embryo sacs and adventive embryos; embryo sac cells are regarded as potential gametes which are capable of giving rise to embryos without fertilization. It allows demonstration of the developmental stage that leads to apomixis. Stages of seed development during amphimixis are presented in the left part of the scheme and types and forms of apomixis are in the right part.
