An irregular mode of reproduction resulting in the development of an embryo without fertilisation is called Parthenogenesis or apogamy or sporophytic budding. Parthenogenesis is a natural form of asexual reproduction in which growth and development of embryos occur without fertilisation. In animals, parthenogenesis means development of an embryo from an unfertilised egg cell. Apogamy, a type of reproduction, occurring in some ferns, in which the sporophyte develops from the gametophyte without the fusion of gametes. Sporophytic budding is a type of apomixis in which an embryo develops directly from the nucellus or integument tissue.