(i) Why does endosperm development precede embryo development in angiosperm seeds? State the role of endosperm in mature albuminous seeds.
(ii) Describe with the help of three labelled diagrams the different embryonic stages that include mature embryo of dicot plants.
(i) The development of endosperm precedes that of the embryo in angiosperm seeds, because the endosperm cells provide nutrition to the developing embryo. In mature albuminous seeds, endosperm exists as storage tissue. It stores starch and fat.
(ii) Development of an Embryo
The first stage in the development of a plant zygote is a pre-determined mode of development (embryogeny). It gives rise to an organised mass of cells called the embryo, that has the potentiality to form a complete plant.
Most zygotes divide only after certain amount of endosperm is formed to assure proper nutrition is provided to the developing embryo. In the majority of angiosperms, the zygote (fertilised egg) divides by an asymmetric mitotic division and generates two cells with two different fates.
(i) The smaller daughter cell with dense cytoplasm is situated towards the chalazal pole side. It is called terminal cell or apical cell or embryonal cell.
(ii) Another, comparatively larger daughter cell situated towards the micropylar cell, is called basal cell. This cell divides transversely and gives rise to suspensor cells. The zygote gives rise to the proembryo and subsequently to. the globular, heart-shaped and mature embryo.
Though the seeds differ greatly, the early stages of embryo development (embryogeny) are Similar in monocots and dicots.
