Absence of light may lead to yellowish colour in plants. This is called etiolation. Light is important for photosynthesis.

It refers to all collective, progressive and deteriorative processes which ultimately lead to complete loss of organization and function.

The photoperiod required to induce flowering is called critical day length

The physiological change on flowering due to relative length of light and darkness (photoperiod) is called Photoperiodism.

Mixture of two phenoxy herbicides 2,4-D and 2,4,5- T is given the name 'Agent orange' which was used by USA in Vietnam war for defoliation of forest (chemical warfare).

The process of maturation of meristematic cells to specific types of cells performing specific functions is called differentiation.

If the length of a plant organ is plotted against time,
it shows a linear curve and this growth is called
arithmetic growth. Mathematically it is expressed as:
L_t = Lo + rt
L_t = length at time '1"
L₀ = length at time zero
r = growth rate, of elongation per unit

The total period from initial to the final stage of
growth is called the grand period of growth

1) Abscission is a physiological process of shedding of organs like leaves, flowers, fruits and seeds from the parent plant body.
2) When these parts are removed the plant seals off its vascular system to prevent loss of water and nutrients. Final stage of senescence is abscission.

Many species of biennials and perennials are induced to flower by low temperature exposure (ODe to 5DC) in the early stages. This process is called Vernalization. The term Vernalization was first used by T. D. Lysenko (1938).

A hormone called florigen is said to induce flowering. The term florigen was coined by chailakyan but it is not possible to isolate it.

1) The effect of two substances in such a way that they  have opposite effects on the same process is called Antagonistic effect.
2) One accelerates and other inhibits. Example: ABA and gibberellins during seed or bud dormancy, ABA induces dormancy and gibberellins break it.

2, 4 - D - 2, 4-Dichlorophenoxy Acetic acid
2, 4, 5 - T - 2, 4, 5- Trichlorophenoxy Acetic acid

There are three phases of growth,
1) Formative phase (cell division phase)
2) Elongation phase (cell elongation phase)
3) Maturation phase

Growth in plants can be measured in terms of,
1) Increase in length or girth (roots and stems)
2) Increase in fresh or dry weight
3) Increase in area or volume (fruits and leaves)
4) Increase in number of cells produced.