EMBRYO

CHAPTER 2                                     SEXUAL REPRODUCTION IN FLOWERING PLANTS

Embryo

[1]  Embryo develops at the micropylar end of the embryo sac where the zygote is situated.

[2]  Most zygotes divide only after certain amount of endosperm is formed.

This is an adaptation to provide assured nutrition to the developing embryo.

[3]  Though the seeds differ greatly, the early stages of embryo development (embryogeny) are similar in both monocotyledons and

dicotyledons.

[4]  The zygote gives rise to the proembryo and subsequently to the globular, heart-shaped and mature embryo.

[5]  A typical dicotyledonous embryo consists of an embryonal axis and two cotyledons.

[1]  The portion of embryonal axis above the level of cotyledons is the epicotyl, which terminates with the plumule or stem tip.

[2]  The cylindrical portion below the level of cotyledons is hypocotyl that

terminates at its lower end in the radicle or root tip.

[3]  The root tip is covered with a root cap.

[4]Embryos of monocotyledons possess only one cotyledon.

[5]  In the grass family the cotyledon is called scutellum that is situated towards one side (lateral) of the embryonal axis.

[6]  At its lower end, the embryonal axis has the radical and root cap enclosed in an undifferentiated sheath called coleorrhiza.

[7]  The portion of the embryonal axis above the level of attachment of scutellum is the epicotyl.

[8]  Epicotyl has a shoot apex and a few leaf primordia enclosed in a hollow foliar structure, the coleoptile.