GA is a terpene derivative. Ethylene is a volatile gaseous hormone. ABA is a derivative of carotenoids. Auxin is an indole compound.

ABA is a hormone which works in stressful conditions. GA acts antagonistic to ABA. Auxin leads to apical dominance. Ethylene is related to early ripening of fruits.

The formation of secondary cell wall around tracheids and vessels is an example of differentiation. Development is overall changes occurring in life cycle of an organism. Dedifferentiation is regaining lost capacity of cells or tissues of plants to divide under special conditions. Redifferentiation is furr maturation of dedifferentiated cells reby specializing for a particular function.

Unlimited growth of plants is due to presence of meristems which are actively dividing cells and are present at tips of root and shoot. The cells of se meristems are small and have dense protoplasm. They also have a high nucleo-cytoplasmic ratio.

Auxin is a hormone which is produced by growing apices of plant. It is transported to or growing region in both acropetal as well as basipetal succession.

Development is sum of two processes-growth and differentiation. To begin with, it is essential and sufficient to know that development of a mature plant from a zygote follows a precise and highly ordered succession of events.

The simplest expression of arithmetic growth is exemplified by a root elongating at a constant rate. On plotting length of organ against time, a linear curve is obtained.

Differentiation is responsible for vacuolization and development of end wall perforation in sieve tube elements. Differentiation is division and growth of cells in order to attain maturity. Dedifferentiation is regaining lost capacity of cells or tissues of plants to divide under special conditions. Redifferentiation is maturation of dedifferentiated cells reby specializing for a particular function. Development includes all changes undergone by a living plant from seed emergence to death.

Open form of growth is exhibited by plants as at tips of root and shoot, continuously dividing cells of meristems are present which are ultimately responsible for ir unlimited growth. Viruses cannot multiply in se continuously dividing cells.

The source of hormone ethylene is ephon. Source of auxin is oats. Source of cytokinin is coconut kernel. Auxin was first isolated from human urine.