The exponential growth or phase of geometrical growth of the plant can be expressed as $W_{1} = W_{0}\ e^{rt}$, where $W_{0} =$ Initial size at the beginning of the period $W_{1} =$ Final size at the beginning of the period $r =$ Growth rate $t =$ Time of growth $e =$ Base of natural logarithms Here, the relative growth rate is also the measure of the ability of the plant to produce new plant material, which is referred to as efficiency index. Hence, the final size, $W_{1}$ depends on the initial size, $W_{0}$