(a) Ovules develop into viable seeds which are capable of germination under suitable environmental conditions. Viability is influenced by various condition like humidity, temperature and availability of oxygen. Viability can be lost due to :
(i) Exhaustion of food around the embryo
(ii) Damage to embryo
(iii) Denaturation of enzymes
(iv) Extremely high temperatures
(v) Excessive dry or damp weather
(b) Development of a dicot embryo:
Zygote is the first cell of early embryo development in flowering plants including bean plant.
The zygote develops after the fusion of male ***** nuclei released from pollen grain with the egg present in the embryo sac. This fusion is called syngamy The embryo develops at the micropylar end of the embryo sac where the zygote is situated.
The zygote divides into a larger cell called suspensor cell towards micropylar end and a smaller cell called embryonal cell towards antipodal cells.
The suspensor cell divides mitotically to form 6-10 celled structure called suspensor. The last suspensor cell is called hypophysis that forms radicle tip. The zygote divides mitotically and gives rise first to the pro-embryo, then to the globular and heart-shaped mature embryo. A typical dicot embryo consists of an embryonal axis and two-cotyledons. The portion of the embryonal axis above the level of cotyledons is called epicotyl. It contains the plumule (***** tip). The portion below the axis is called hypocotyl. It contains the radicle (root tip). The root tip is covered by the root cap.
(c) When zygote forms the embryo the endosperm provides nourishment to the growing embryo. During this, the endosperm is utilised and eaten up. In the seeds like pea, gram etc. endosperm is completely eaten up by the growing embryo and the food for later development of embryo is stored in cotyledons which become massive. Suchieeds are exalbuminous. While in seeds like castor and maize the endosperm persists in the seed as food storage tissue and such seeds are albuminous.
