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Plant Growth and Development

Growth is a characteristic feature of all living organisms. Growth is a vital process which brings about permanent and irreversible change in any plant or its part Growth in plants means increase in shape, size, weight and volume of a plant or plant part. Growth leads to increase in fresh weight, dry weight, length, area, volumed and cell number and all these are controlled extrinsicly (by environmental factors) and intrinsicly (by nucleus and protoplasm).

Growth is diffused in animals but growth in plants is localised & irregular. (Nail in plant stem, occupies same height till several years of growth).

Seed germination is the first step of plant growth. Almost all the plants face a period of suspended growth.

If the suspension of growth is due to exogenously controlled factors (environmental factors) then it is called quiescence.

When the suspension of growth is due to the endogenously controlled factors (hormonal, genetic) then it is termed as dormancy.

Weight is increased during growth but exceptions are potato & seed germination where weight decrease.


Differentiation: Cells derived from active meristem tissue become mature to perform specific function,

Development: Sum of morphogenesis and differentiation activities in livings is called as development.

Dedifferentiation: In plants the living differentiated cell which lost the capacity of cell division, regain the capacity of cell division under certain conditions called dediffentiation.

Ex. Formation of meristems intrafascicular cambium & cork from differentiated parenchyma cells.

Redifferentiation: The regain of differentiation by losing the capacity of cell division for performing specific function by a dedifferentiatied cells.

Determinate/Limited Growth: Growth activities in some plants limited for specific period of time or season called as determinate/limited growth.

Ex. Annuals & Biannuals.

Regions of growth: In unicellular plants there is overall growth and not confined to any specific region but in multicellular plants growth is restricted to specific regions having meristematic cells. On the basis of their position in the plant body (higher plants) meristems are divided into these main categories.

Apical meristems: These meristems are found at shoot and root apex. As a result of activity of these meristems plant increases in length. In angiosperms and gymnosperms there is a group of meristematic cells but in bryophytes and pteridophytes there is a single tetrahedral cell found at the shoot apex:

Intercalary meristems: These meristems are found above the nodes. As a result of the activity of these. meristems increase in length takes place. e.g., Bambusa.

Lateral meristems: These meristerns are made up of cells which divide in radial direction only. They form laterally placed new cells towards the centre and periphery. Cork cambium (phellogen) and vascular cambium are' the examples of lateral meristems. Increase in girth of shoots and roots take place because of the activity of this cambium 


Phase of cell division or cell formation: Number of cells increases by cell division.

Phase of cell enlargement or cell elongation: Size of cells increased due to vacuolization & TP (Turgor pressure).

Cell maturation or differentiation phase: (Also called as Morphogenetic, Organogenic phase) Development or qualitative change is important feature of this phase.


(Growth curve)

The pioneering work on growth was done by Von Sachs.

He plotted a growth curve between time & growth which is known as sigmoid curve or S-curve or GP (Grand period)-curve.

Growth pattern of cell, organisms is uniform under favourable conditions. Thus following phases of growth are recognized.

(i) Lag phase: In lag period the growth is slow. It represents formative or cell division phase.

(ii) Log phase: Also called as exponential phase. During this phase growth is maximum & most rapid. It represents cell elongation phase.

(iii)  Steady or stationary phase: It represents cell maturation phase.

 Time taken in growth phases (mainly log phase) is called as grand period of growth.

Growth curve



(i) By direct observation

(ii) By Horizontal Microscope

(iii) By Crescograph (J.C. Bose): It magnify growth as 10,000 times

(iv) By Auxanometers

(a) Arc - Auxanometer

(b) Pfeffer's Auxanometer pully Auxanometer (permanent graph on smoke paper).

(c) Micrometer Screw - Auxanometer

Growth can be measured by an increase in size or area of an organ of the plant (leaf, flower, fruit etc.) in a unit time and is called as efficiency index. E.I. may be same or differ by species to species and organ to organ.


1. Light: Light involved in photosynthesis and determine the direction of shoot and root growth. Light controlled morphogenesis of plant is called photo morphogenesis.

Light is not essential during the initial stage of growth or seed germination. In absence of light plant exhibit etiolation.

2. Temperature: Optimum temp for growth is 20- 35°C. Temp. above 45°C damages the protoplasm and growth is retarted.

Effect of low temperature on flowering is called vernalization.

3. Water: Water maintains the turgidity of cell, which is essential for growth. TP is important for growth. In order to cell to grow ψw must not be allowed to reach zero. Water is essential for the enzyme activity in protoplasm.

4. Oxygen: Necessary for cell respiration.

5. Mineral nutrients: All essential elements are compulsory for growth and metabolism.

6. Genetic factors: Genotype & Phenotype.

7. Pollutants: Several pollutants such as automobile exhaust, peroxyacetyl nitrate (PAN), pesticides etc have detrimental effect on plant growth. Citrus and Gladiolus are very sensitive to fluorides. Poor; growth of tobacco is observed in regions Where ozone concentration is high. Cotton plants are similarly very sensitive to ethylene.

8. Carbon dioxide: CO2 is essential for photosynthesis and hence nutrition. Due to change in photosynthetic rate, with the increase or decrease in concentration, the plant growth is also affected.

9. Nutrition: It provides raw material for growth and differentiation as well as source of energy. C/N (Carbohydrate/Nitrogen) ratio determines the type of growth. High C/N ratio stimulates' wall thickening. Less protoplasm is formed. Low C/N ratio favours more protoplasm producing thin walled soft cells. According to law of mass growth, the initial rate of growth depends upon the size of germinating structure (seed, tubes, rhizome, bulb, etc.)

 10. Growth regulators: These are manufactured by living protoplasm and are important internal growth regulators which are essential for growth and development. These growth regulators include several phytohorrnones and some synthetic substances. 

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