Germination is a process by which an organism puts its buds forth from a seed. There is a sequence of events in germination process. The germination process of seeds is a series of events which are given as follows:
- Imbibition (absorption of water)
- Hydration of protoplasm(see streaming of protoplasmic theory)
- Activation and synthesis of enzymes
- Increase in respiration
- Increased synthesis of nucleic acids and proteins
- Synthesis and release of hormones from embryo
- Increased cell enlargement and cell division
- Hydrolysis of deserved food substances in endosperm and cotyledon
- Utilization of soluble organic substances by developing embryo
- Growth of radicle into root and plumule into shoot
Difference between growth and development
Germination process of seeds start with imbibition followed by its growth. Growth is the increase in the size of plant or other words quantitative increase in plant body. An irreversible increase in the size of the plant body is growth. Imbibition of water and an increase in the size of wood is not considered to be growth.
Similarly, an increase in the size of seed after absorption of water is not a growing phenomenon. In both cases, size becomes reverted upon drying. Growth is limited to living organisms only. Growth is not taking place in the entire seed or tuber, but it takes place only in specific regions.
It refers to the qualitative changes taking place in the plant body, for example, germination of seed, falling of leaves, and others. Things improve in the development process. Growth and development are not two different phenomenons occurring at different times.
On the other hand, one follows the other in quick succession. When meristem changes from vegetative to reproductive stage, this change is development. So the life of the plant is divided into two phases:
Vegetative phase that occurs from the emergence of seedling till flowering.
Reproductive phase occurs from the initiation of flowering till the completion of seed formation.
Phases of growth
It is an important phase of plant growth. It starts from unicellular zygote to a multicellular embryo and then develops into a plant. The size of the plant depends upon the number of cells and the size of cells.
The expansion is predominantly in the longitudinal direction. It may have the same meaning as cell elongation.
With the division of and enlargement of cells, these newly formed cells undergo mutation or specialization. During this, cells change their shape. Cell walls undergo thickening. Often lignin and suberin deposit on the walls. This process of specialization of cells to perform different functions is differentiation.