BOTANY Higher Secondary Second Year - Textbooks Online

5.4. Plant growth
Growth is one of the most fundamental and conspicuous characteristics
of living organisms. Growth may be defined as an irreversible increase in
mass, weight and size of a living organisms. In most cases, it results in
increase in dry weight and the amount of protoplasm. Growth in higher
plants includes cell division, enlargement and differentiation. Increase in
the number and size of cells by itself cannot account for the development
of an organized plant. For example, when a seed is sown, it does not
become a larger seed but it grows as a seedling. Thus, growth is always
accompanied by differentiation. Differentiation is the transformation of
identical cells into different tissues. Depending upon the various structural,
functional and physiological needs of the plant the tissues are of different
types. Growth and differentiation results in development, which leads to
gross form of the plant. Meristematic cells present in the plant body viz.,
root, shoot apices, and the cambium are responsible for growth in plants.
Phases of growth
The growth in length of the plant is due to the meristematic activity of
the apical meristems that takes place in the root and shoot apices. Whereas
increase in thickness of stem and root is due to the activity of lateral
meristem. You have already learnt in chapter 2 about different types of
meristems. The period of growth is generally divided into three phases
Growth rate
Lag phase
Time
Fig. 5.24 Sigmoid curve
Steady state phase
Log phase
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viz., formation, elongation
and maturation. In the first
phase, new cells are
continuously formed by the
apical meristem. In the
second phase known as
phase of elongation, the
newly formed cells enlarge
in size. In the third phase,
phase of maturation, cells
start maturing to attain
permanent size and form.
The rate of plant growth is
slow in the initial stages and