Question

Describe with the help of three labelled diagrams the different embryonic stages that include mature embryo of dicot plants.

Answer 1

Following are the steps that occur during the development of an embryo:

First, the zygote starts dividing and gives rise to proembryo. This proembryo further divides, forming a globular, heart-shaped mature embryo. A typical dicot embryo consists of an embryonal and two cotyledons.

The portion of the embryonal axis above the level of cotyledons is called epicotyl. It contains the plumule(shoot tip). The portion below the axis is called hypocotyl. It contains the radicle(root tip). The root tip is covered by the root cap.

Answer 2

Development of a dicot embryo:-

(i) Embryo formation starts after a certain amount of endosperm is formed.
(ii) Zygote divides by mitosis to form a proembryo.
(iii) Formation of globular and heart-shaped embryo occurs, which finally becomes horse shoe-shaped forms a mature embryo.
(iv) In dicot plants, embryo consists of two cotyledons and an embryonal axis between them.
(v) The portion of embryonal axis above the level of attachment of cotyledons is epicotyl and it terminates in the plumule.
(vi) The portion of embryonal axis below the level of attachment of cotyledon is the hypocotyl, it becomes radicle (root tip).

The embryonic stages during the development of a mature embryo sac are: 

(a) Fertilised embryo sac showing zygote and Primary Endosperm Nucleus (PEN).
(b) Stages in embryo development in a dicot.