1. In plants, growth curve is always sigmoid, i.e. S-shaped. This is because growth starts slowly during formative phase, becomes rapid during elongation phase and finally slows down to a steady state during the maturation phase.
2. The standard growth curve shows three phases, viz. lag phase, log phase and stationary phase.
(i) Lag phase or initial growth phase : This is the initial phase of growth. During this phase of growth, the rate of growth is slow. It corresponds to formative phase of growth where new cells are formed due to cell division.
(ii) Log phase or exponential phase : This is the second phase of growth. During this phase, the growth is rapid and maximum. It corresponds to the phase of cell elongation.
(iii) Stationary phase or steady phase : The stationary phase is the third and last phase of growth. In this phase, growth slows down and becomes steady. The cells undergo differentiation during stationary phase.