Sexual propagation involves the union of the pollen (male) with the egg (female) to produce a seed. The seed is made up of three parts: the outer seed coat, which protects the seed; the endosperm, which is a food reserve; and the embryo, which is the young plant itself. When a seed is mature and put in a favorable environment, it will germinate, or begin active growth.
Germination is a biochemical process that involves the activation of many chemical reactions. This happens in three stages. Thefirst stage of seed germination involves the uptake of water. This is called imbibition. During imbibition the protein synthesizing systems are activated and various enzymes are synthesized. These enzymes catalyze reactions used in the second stage of germination. The second stage of germination involves the breakdown of the stored energy rich compounds of the cotyledons and endosperm. The second stage is a period of readying the embryo for rapid growth during the third stage. This is the Lag sphere. During the third stage of germination, cell division begins and the embryo grows into a seedling. Thefirst growth occurs in the radicle and the root system is established. There are environmental factors which affect germination.
Thefirst step in the germination process is the imbibition or absorption of water. Even though seeds have great absorbing power due to the nature of the seed coat, the amount of available water in the germination medium affects the uptake of water. An adequate, continuous supply of water is important to ensure germination. Once the germination process has begun, a dry period will cause the death of the embryo.
Light is known to stimulate or to inhibit germination of some seed. The light reaction involved here is a complex process.
In all viable seed, respiration takes place. The respiration in dormant seed is low, but some oxygen is required. The respiration rate increases …