Phases of Growth in Plants: In general there are three phases of growth in Plants: Elongation, Meristematic and Maturation.

Phases of Growth in Plants

Meristematic or Formative Phase 

The tip region of the roots (lower part of the plant) and the Shoot (upper part of the plant) consists of the meristematic tissue as it always keeps growing. 

• The meristematic cells in this region divide continuously and are isodiametric (with no spaces between the cells).
• The zone is referred to as the meristematic zone.

The characteristics of Meristematic cells in the Formative Phase are:

• The cells in the meristematic zone have rich protoplasm. 
• The cell walls are primary in nature. They are thin and have cellulose.
• The cells in the meristematic zone have white plasmodesmata connection.
• Plasmodesmata is a microscopic cytoplasmic canal, passing through the plant cell walls. 
• It allows molecules to communicate directly with the adjacent plant cells.
• Meristematic cells have a large and conspicuous nucleus.
• These cells keep dividing vigorously. 

Elongation Phase

The cells which are present in the next region after the meristematic cells belong to the elongation region. The enlargement of the cell takes place in the elongation phase. This phase is also marked by the formation of the new cell wall, vacuoles, etc.

The characteristics of the cell in the Elongation Phase are:

• The elongation of these cells takes place due to the enlargement of the vacuole in the cell and therefore the zone is known as the zone of elongation.
• These cells have an increased number of vacuoles. 

Maturation Phase

The cells in the maturation phase achieve their maximum size. They do not further divide into cells. The maturation zone is found as the mass differentiation phase where cells differentiate to perform special functions.

The cell in the Maturation Phase have proper wall thickening and protoplasmic modifications of the cells take place.

After studying all three phases of cell growth the three main processes which occur in these phases are – 

• Cell division – The division of a cell into two daughter cells with the same genetic material
• Cell enlargement – The cells increase in size
• Cell differentiation – The process during which young, immature (unspecialized) cells take on individual characteristics and reach their mature, specialised form and function.

The first two stages of plant growth can lead to an increase in the plant size whereas the third phase is more marked to bring maturity in the cells. During differentiation, the cells show structural changes in the protoplasm and the cell wall.

Growth Rates

The number of cells in organisms increases in a number of ways. The growth rate is the increase in growth per unit of time. This can be expressed mathematically by a formula.

There are two types of growth rates in plants: Arithmetic and Geometric Growth Rates.

1. Arithmetic Growth in Plants:

Mitosis is a process of nuclear division that occurs when a parent cell in eukaryotic cells divides to produce two identical daughter cells.

• When the plant cells undergo mitotic division, two cells are formed out of one cell. 
• Out of these two cells one cell continues dividing and the other one gets differentiated and forms a different structure. 
• The former cell again divides and forms two more cells and then one continues dividing and there is one more that is differentiated. 
• Now there are two differentiated cells from the one cell initially. 
• Similarly, by following this a pattern is formed and a gradual increase in the size of the plant takes place.

To calculate Arithmetic Growth, the Formula is:

L_t = L₀ + rt 

Where,

• L= length of the plant
• L_t = length at time ‘t’ or after time ‘t’
• L₀ = Length at initial time
• r = rate of growth
• t = time interval when we are calculating the plant growth rate

2. Geometric Growth in Plants

Through geometric growth, the cell divides by mitotic division and two cells are formed. Both the cells then again divide to form two more cells for each. Thus, now the number of cells doubles at each stage. 

• The number of cells will be like 2, 4, 8, 16, 32, 64, …and so on, unlike arithmetic growth stages, here no differentiation of cells takes place. 
• The cell growth rate is rapid here in the geometric phase. 
• When the growth reaches its peak, it becomes slow and later becomes steady due to some limiting factors. 

The geometric plant growth can be represented in the form of an S-shaped graph given as a Sigmoid Growth curve in plants.

• Lag Phase- It is the slower phase where cell division is slow at the beginning.
• Log Phase- A steep curve is formed here. The growth is very fast here. And it is also known as the exponential phase too.
• Stationary or Steady Phase- In this the growth is steady or stationary. It can be stated that growth becomes constant.

Formula that Represents this Sigmoid Growth Curve is as Follows:

W_t = W₀ * e^rt

Where, 

• W₀ = size at the initial time
•  W_t= size at time t or after time t
•  r = growth rate
•  t = time period
•  e = base of natural logarithm

Growth is a natural process and unlike human beings plants have different forms of growth and carry out it in a very different way. The process which helps the growth to the fullest is the particular process known a photosynthesis. It is the process that plants perform in the presence of sunlight, water and organic compounds in order to produce food in the form of ATP. This helps the plant to grow and to provide energy to each and every cell of its structure.

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By Team Learning Mantras