. Explain Briefly Parts of Seeds
PARTS OF SEEDS:
1. SEED COAT
i. It is the outer covering of the seed. It develops from integuments of the ovule. In most of the seed, the seed coat is made of two layers. The outer layer is called testa and the inner layer is tegmen. Seeds developing from the unitegmic ovules (i.e., ovules with one integument only) have single layered seed coat. The function of seed coat is to protect the delicate embryo within.
ii. The seed remains attached to the pericarp (fruit wall) by a short stalk called seed stalk or funicle. In a mature seed the position of seed stalk is represented by a small oval depression called hilum.
i. The young or miniature plant, enclosed within the seed coat is called as embryo. It develops from the fertilized egg. Embryo has two parts, cotyledon and embryonal axis (tigellum).
ii. The point on tigellum where cotyledons get attached is called as cotyledonary node. The part of tigellum lying immediately above the cotyledonary node is known as epicotyl and at the tip of epicotyl lies the plumule. It gives feathery appearance due to presence of one or more leaf primordia i.e., young leaves at its apex.
iii. The part of the tigellum below the cotyledonary node is known as hypocotyl. It represents the root stem transition region i.e., the part where stem changes into root. The radicle is the basal part of hypocotyl. Externally the radicle may or may not be differentiated from the hypocotyl but these two parts are quite different.
iv. In seeds, food is stored either in the cotyledons or in a special food storage tissue (endosperm). In legumes, for example, the food is stored chiefly in the cotyledons and there is no endosperm. Absence of endosperm in seeds indicates that it (the endosperm) has been completely utilized by the developmg embryo. Such seeds are known as non-endospermic or exalbuminous. In some dicotyledons, e.g., castor, and in monocotyledons e.g., cereals and grasses, food is stored mainly in the endosperm and such seeds are known as endospermic or albuminous.