Cytohistological zonation theory:
This theory was proposed by poster in 1939.
Shoot apical meristem is classified into two regions on the basis of rate of division. They are a) Summit and b) Flanks they are present in two types of shoot apex
1) Vegetative Shoot Apex
2) Reproductive Shoot Apex
1) Vegetative Shoot Apex:
Vegetative shoot Apex helps in the growth of plant, it is a dome shaped structure.
It consist of fallowing two regions
i) Summit: The rate of cell division is quite slow in this region. This region is located at the Apex
ii) Flanks: The rate of division is very fast in this region. This region lies behind/below the summit and leaf primordia are formed by this region.
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| Vegetative shoot Apex |
2) Reproductive Shoot Apex:
Reproductive shoot Apex is Broad Or Flat in Shape. This region help for the formation of reproductive structure of the plant that is which forms the flower of the plant.
It also consist of fallowing two regions:
i) Summit: In this region the cells are more active and the rate of cell division is fast. This part help for the formation of Stamens(Androcium) and Carpel(Gynocium).
ii) Flanks: In this region the cell ate less active and the rate of cell division is slow. This forms Sepal(Calyx) and Petals(Corolla).
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| Reproductive shoot Apex |
At the time of flowering vegetative shoot Apex transforms onto reproductive shoot Apex this change of shoot apex is induced by florigen and light.
Function of leaf primordia is it provides protection to shoot Apex.
