When gametophytes grow upon the soil and form independent plants “Exosporic”

eg: Psilotum, Pteris, Lycopodium

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Intercalary meristem

They occur in grasses and regenerate parts removed by the grazing herbivores

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Lateral meristem

Present on lateral side and increases thickness, girth and diameter

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Lateral meristem

They are cylindrical meristems

Examples of lateral meristems- vascular cambium and cork-cambium

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Vascular Cambium

The meristematic layer that is responsible for cutting off vascular tissues – xylem and pholem – is called vascular cambium

young stem it is present in patches as a single layer between the xylem and phloem. Later it forms a complete ring

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Formation of cambial ring

The cells of medullary rays, adjoining these intrafascicular cambium become meristematic and form the interfascicular cambium. Thus, a continuous ring of cambium is formed

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Activity of the cambial ring

Cambial ring becomes active and begins to cut off new cells, these cut off cells towards pith, mature into secondary xylem and the cells cut off towards periphery mature into secondary phloem