Difference between apical and lateral meristems are
Apical meristems - It is present at the growing tip of the stem and roots and increases the lenght.
Lateral meristems - It is present at the lateral side of stem and root (cambium) and increases the girth.
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apical meristem : apical meristem helps in the growth of the plant it is found in the growing tips of the plant.
lateral meristem : lateral meristem helps to increase the girth of the plant. 
             i hope that this will help u.
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