cleavage Polyembryony:
The production of plural embryos by the splitting of the zygote is termed cleavage polyembryony. It is a common feature in Gymnosperms but it is rare in Angiosperms. When it does occur, it is only after the zygote has undergone a few irregular divisions and has formed a group of embryonic cells.
This group continues to increase in volume and outgrowths arise at its lower end which finally function as independant embryos. This condition is observed in Erythronium americanum, Cocos nucifera, etc.
Cook (1902) observed an embryo sac of Nymphaea advena showing twin embryos which should be considered to have originated by the splitting of a very young embryo. The same author also observed four embryos at the micro-pylar end of the embryo sac of Crotalaria sagittalis. These embryos are believed to have arisen by a splitting of the single zygotic embryo.
It is only in the family Orchidaceae that the cleavage polyembryony is quite common. In Eulophia, Swamy (1943) recorded three different modes of supernumerary embryo formation.
1. The zygote divides irregularly to form a mass of cells of which those lying toward the chalazal end grow simultaneously and give rise to many embryos.
