Explain the development of a Dicot embryo.

Explanation

Development of Dicot embryo:
Development of Dicot embryo (Capsella bursapastoris) is of Onagrad or crucifer type. The embryo develops at micropylar end of embryo sac.
(i) The Zygote divides by a transverse division forming upper or terminal cell and lower or basal cell. The basal cell divides transversely and the terminal cell divides vertically to form a 4 celled proembryo.
(ii) A second vertical division right angle to the first one takes place in terminal cell forming a 4 celled stage called quadrant.
(iii) Transverse division in the quadrant results in 8 cells arranged in 2 tiers of 4 each called octant stage.
(iv) Upper tier of 4 cells of the octant is called epibasal or anterior octant and the lower tier of four cells constitute hypobasal or posterior octants.
(v) A periclinal divison in the octants results in the formation of 16 celled stage with 8 cells in the outer and eight in the inner.
(vi) The outer 8 cells represent the dermatogen and undergoes anticlinal division to produce epidermis.
(vii) The inner 8 cells divide by vertical and transverse division to form outer layer of periblem which give rise to cortex and a central region of pleurome which froms stele. During the development, the 2 cells of the basal cell undergoes several transverse division to form a 6 to 10 celled suspensor.
(viii) The embryo at this stage become globular and the suspensor helps to push the embryo deep into the endosperm.
(ix) The uppermost cell of the suspensor enlarge to form a haustorium. The lowermost cell of the suspensor is called hypophysis.
(x) A transverse division and two vertical division right angle to each other of hypophysis results in the formation of 8 cells.
(xi) The eight cells are arranged in two tiers of 4 cells each. The upper tier give rise to root cap and epidermis.
(xii) At this stage embryo proper appears heart shaped, cell divisions in the hypocotyl and cotyledon regions of the embryo proper results in elongation.
(xii) Further develoment results in curved horse shoe shaped embryo in the embryo sac. The mature embryo has a radicle, hypocotyl,two cotyledons and a plumule.