In arithmetic growth, following mitotic cell division, only one daughter cell continues to divide while the other differentiates and matures. The simplest expression is exemplified by a root elongating at a constant rate. On plotting the length of the organ against time, a linear curve is obtained. Mathematically, it is expressed as Lt = L0 + rt, where Lt is length at time 't', L0 is length at time 'zero', and r is growth rate per unit time.

In geometric growth, the initial growth is slow called the lag phase, and it increases rapidly thereafter at an exponential rate called the log or exponential phase. Here, both the progeny cells following mitotic cell division retain the ability to divide and continue to do so. However, with limited nutrient supply, the growth slows down leading to a stationary phase.

When we plot the parameter of growth against time, we get a typical sigmoid or S-curve. A sigmoid curve is a characteristic of living organisms growing in a natural environment. It is typical for all cells, tissues and organs of a plant.

The absolute growth rate is the measurement and comparison of total growth per unit time. The relative growth rate is the growth of the given system per unit time expressed on a common basis, e.g., per unit initial parameter. Two leaves of different sizes may show the same absolute increase in area in a given time, but one of them shows much higher relative growth rate.