Seed

The fertilized ovule forms seed. The study of seed is called spermology.

The seeds are of two types:

(1) Non endospermic or Exalbuminous seeds: In seeds like gram, pea, groundnut, etc. the endosperm is completely consumed by the embryo, thus the seeds are called non-endospermic or exalbuminous e.g., dicots.

The seed coat is formed by integuments. The outer seed coat called testa develops from outer integument and inner seed coat called tegmen is derived from inner integument. The food is stored in the cotyledons.

(2) Endospermic or albuminous seed: In monocots and castor bean (dicots) embryo does not consume all endosperm. So it persists in the mature seed. Such seeds are called endospermic or albuminous seeds. In these seeds food is stored in endosperm.

Perispermic seeds. Mostly nucelus is consumed after fertilization due to absorption of food by the endosperm and embryo. The remains of nucelus in the seed is called perisperm. Such seeds are called perispermic seeds e.g. Piper nigrum .

Chalazosperm is perisperm like tissue in chalazal region. It is a substitute for endosperm e.g., Cynastrum.

 

Parts of a seed:

 The seed is covered by a seed coat which is protective to the embryo. It has two coverings-outer testa and inner tegmen. Seed coat has an aperture for entry of water called micropyle. Inside the seed lies the embryo which consists of (i) cotyledons - they are specialized leaves storing food material. (ii) A short axis called tigellum, to which cotyledons are attached. This axis has two parts- the radicle which develops into root, and plumule developing into shoot.