Explain different phases of growth.
Plant growth has following three phases
(i) Meristematic Phase - This phase is characterised by constantly dividing cells. The cells are rich in protoplasm, possess large conspicuous nuclei. Their cell walls are primary in nature, thin and cellulosic with abundant plasmodesmatal connections.
(ii) Elongation Phase - The cells of this phase elongate. Increased vacuolation, cell enlargement and new cell wall deposition are the characteristics of the cells in this phase.
(iii) Maturation Phase - The cells in this phase stop dividing and undergo differentiation and maturation.The cells of this zone, attain their maximal size in terms of wall thickening and protoplasmic modifications.
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.