Growth is most important phenomenon because of following reasons :
1. Due to growth, size of the organism, increases.
2. The growth results in increase in weight, mass and size of the organism.
3. Growth allows the cells to be differentiated. e.g. In roots, the cells first elongate in the zone of elongation and then in the zone of differentiation they are differentiated into tissues and organs.
4. It is due to growth that radical forms root and plumule forms the stem during germination of the seeds.
5. It is due to growth that buds sprout to form the branches.
8. It is due to the growth that floral buds sprout to form flowers.
9. It is due to the growth of pollen grains and functional megaspore cells that male and female gametophytes are formed respectively.
10. It is due to the growth that pollen tubes grow and siphonogamy occurs.
11. The fruits are formed due to the growth of the ovary.
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.