The seed, or matured ovule is made up of three parts. The embryo is a miniature plant in an arrested state of development. Most seeds contain a built-in food supply called the endosperm (orchid are an exception). The endosperm can be made up of proteins, carbohydrates or fats. The third part a hard outer covering called a seed coat. It protects the seed from disease and insects, and prevents water from entering the seed which would initiate the germination process before the proper time.
Germination is the resumption of active embryo growth. Prior to any visual signs of growth the seed must absorb water through the seed coat and micropyle. In addition, the seed must be in the proper environmental conditions; that is, exposed to oxygen, favorable temperatures, and for some correct light. The radicle is the first part of the seedling to emerge from the seed. It will develop into the primary root from which root hairs and lateral roots will develop. The portion of the seedling between the radicle and the first leaflike, (plumule), are attached to a structure called thehypocotyl which becomes the stem. The seed leaves and cotyledons encase the embryo and are usually different in shape from the leaves that the mature plant will produce. Plants producing one cotyledon fall into the group of monocotyledons or monocots. Plants producing two seed leaves are called dicotyledons or dicots.
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