EMBRYO DEVELOPMENT
Embryo develops from zygote at the micropylar end of embryo sac. The nutrition for development is provide by endosperm. The zygote divides to form pre-embryo. The different stages of the developing pro- embryo are globular and heart shaped embryo, which finally forms mature embryo.
EMBRYOGENY IN DICOTS The zygote undergoes transverse division forming a large basal cell and a small apical or terminal cell. The large basal cell enlarges and undergoes transverse division to form a group of 6-10cells called suspensor. The first cell of the suspensor towards the micropylar end is called haustorium, whereas the last cell of the suspensor toward the chalazal end is called is hypophysis that later develop into radical.
The smaller terminal or apical cell undergoes one vertical division. The two cells formed from terminal cell divide by transverse division thus forming four embryonic cell( quadrant stage ). Finally these four cell divide vertically forming 8 celled pre-embryo (octate stage). Four cells at the apex give rise to plumule and another four give rise to hypocotyl except its tip.
STRUCTURE OF DICOTYLEDONOUS EMBRYO A typical dicotyledonous embryo consists of an embryonic axis and two cotyledons. The portion of embryonic axis above the level of cotyledons is the epicotyl, which develops into plumule or stem tip. The cylindrical portion below the level of cotyledon is hypo, which develops into radical or root tip. The root tip is often covered with a root cap
A typical monocotyledonous embryo A typical monocotyledonous embryo consists of one cotyledon. The cotyledon is situated on one side (lateral) embryonic axis and is called scutellum. The radical and root cap are situated at lower end of embryonic axis in an undifferentiated sheath called coleorrhiza. The shot apex and few leaf primordia is enclosed in hollow foliar structure in epicotyl region called coleoptile. The portion of the embryonic axis above the level of attachment of scutellum is called epicotyl.