• In plants development is considered as the sum of these processes – (1) Growth and (2)
• During this process a complex body organisation is formed that produces roots, leaves, branches,
flowers, fruits, seeds eventually they die.
• Growth can be defined as an irreversible increase in the size and weight also number of the cells of
an organism. Physiologically speaking, growth is an outcome of metabolism. There is an increase in
the dry weight as an outcome of growth.
• In plants, growth is limited to meristematic tissues only. There are three main activities involved in
the process of growth – (1) Cell division of meristemic cells. (2) Enlargement of newly formed cells.
(3) Cellular differentiation.
• Growth in length is called- primary growth and growth in the girth is called- secondary growth. The
increased growth per unit time is known as growth rate.
• Growth is divided in to three phases: (1) Phase of cell division. (2) Phase of cell enlargement and (3)
Phase of cell differentiation. The entire period, covering the period from cell divison to cell
differentiation is called grand period of growth.
• Some cells lose power of division and acquire definite characteristics and become permanant tissue.
This are called differentiated cells. Such differentiated cells regain their power of division under
specefic conditions; this cells are called dedifferentiated cells (eg. root cambium)
• Factors which affect growth are water, oxygen, temperature, light and nutrients. For a more exact
measurement of growth in length of a plant, an auxonometer is used.
• Development is a term that includes all changes, that an organism goes through during its life cycle
from germination of the seed to senescence. The plant growth regulaters (PGRS) are small, simple,
molecules of diverse chemical composition. Such chemicals are called plant-growth regulators or
plant hormones. They are classified in to five main groups: (1) Auxins, (2) Gibberrelins, (3) Cytokinins,
(4) Abscisic acid and (5) Ethylene. Some of the vitamins also act as growth-regulators.
• Seed dormarcy is defined as a state in which seeds are prevented from germinating even under
environmental conditions or external factors normaly are favorable for germination. There are mainly
four types of dormancy: (1) Exogenous dormancy, (2) Endogenous dormancy, (3) Combinational
dormancy, (4) Secdonary dormancy. The entire process from the showing of the seed in the soil to
the emergence of a young sapling, consititutes germination. “Mangrooves” are a special type of
vegetation which live in the basin (creek) region around sea-shore. They exhibit a different kind of
germination, Such a germination is called “Viviparous germination”.
• Senescence is a period between complete maturation of an individual and the death of that individual.
The phenomenon of the dropping of leaf, flower and fruit is called-abscission. In the development