The Fine Structure of the Change from the Free-Nuclear to Cellular Condition in the Endosperm of Chickweed Stellaria media

Four types of wall formation occur in the endosperm of chickweed Stellaria media (L.) Cyrill. Freely growing walls form at the edges of the micropylar region of the embryo sac during the early heart stage of embryogenesis; Golgi and dilated endoplasmic reticulum may be sources of precursors for these anastomosing walls which form independently of a mitotic spindle Other walls form by means of cell plates and in a manner similar to wall regeneration reported in protoplasts. Also, wall ingrowths of the transfer cell type form on the embryo sac wall in the micropylar region and protrude into the endosperm.