Quantitative comparisons between the growth of living system can be made in two ways :
(i) By measuring and comparing the total growth per unit time. This is called the absolute growth rate.
(ii) The growth of the given system per unit time expressed on a common basis, e.g., per unit initial parameter. This is called the relative growth rate.
Auxins are of two types :
(1) Natural auxins : These are naturally occuring auxins, isolated from plants and are regarded as phytohormones e.g. IAA. NAA etc.
(2) Synthetic auxins : These are synthesized by artificially e.g. IBA 2,4-D etc.
Auxin was isolated by F.W. Went from tips of coleoptiles of oat seedling.