This paper compares two ways of representing some of the existing growth fu
nctions, i.e., the exponential, the monomolecular or Mitscherlich, the logi
stic or autocatalytic, the Gompertz, and the Richards equations. A second o
rder exponential polynomial will be discussed as well. In the first express
ion growth is expressed in the parameters mass at time zero W-o, mass at ti
me infinity W-f, and a measure for the relative growth rate k. In the secon
d expression different parameters are used because of robust parameter opti
mization (e.g., by the statistical software package Genstat). This paper sh
ows the relationships between these fitted parameters and the parameters W-
o,W-f and k. This paper addresses the properties of these models, such as p
hysical meaning of the parameters, properties at the point of inflection (i
f existing), and the growth rate in the limit W --> 0. The second order exp
onential polynomial is rewritten in such way that use is made of a proporti
onality constant, being equal to the relative growth rate at point of infle
ction. Application of the growth models is demonstrated using data of lettu
ce grown on nutrient film. Finally, it is shown that, except for the expone
ntial polynomial, all growth equations originate from one single equation.