Basics

• Seeds come in two basic varieties: monocot and dicot, meaning they contain either one or two leaves. A seed consists of a number of different components, including the hilium, the microphyle, plumule, the seed coat, the embryo and the endosperm. The seed coat, endosperm and embryo are the three main parts.
  
  

Seed Coat Basics

• The seed coat is the part of the seed that you see when you pick it up, the outer membrane. This coating is usually hard and seamless and its main job is to protect the inner parts from weather, bugs and drops in temperature. The seed coat is most important during the seed's dormant period and splits open during the process of germination.
  
  

Types of Seed Coat

• Depending on the type of seed, the coat can be either thick or thin. In thick seed coats, it is difficult to initiate germination as the coat is too thick for light and water to penetrate to the embryo inside. Most thick-coated seeds are meant to be digested by animals. The process of digestion strips the thickness from the seed coat, leaving it intact but soft and penetrable enough to initiate germination. Scarification or nicking the seed coat with a sharp blade is another way to initiate germination in thick-coated seeds.
  
  A thin seed coat has little defense against water penetration and is designed to respond to light rather than water in order to germinate.
  
  

Endosperm

• The endosperm lies right beneath the seed coat and provides food to the embryo area of the seed. These nutrients during dormancy keep the seed viable. This job is transferred to the cotyledon upon germination and during initial growth.
  
  

Embryo

• The embryo is the most essential part of a seed--the new plant develops from inside. It consists of three main parts: the main root of the plant to be, the cotyledon and the embryonic leaves.
  
  The main root is the how water is absorbed into the embryo to initiate germination and growth. As the plant grows, the main root will be joined by numerous small secondary roots to help increase water absorption from the soil. Another name for the embryonic root is the radicle.
  
  The embryonic leaves are the primary leaves of the new seedling and absorb the nutrients inside the seed. These leaves are contained within the epicotyl, which also contains the initial shoots of the seedling.
  
  The cotyledons are the sections of the seed that surround the leaves and roots and supply nutrients to the seedling. It is the food storage compartment of the seedling. The cotyledon can sustain the new plant for up to ten days after the seed pod explodes during germination.