Plant growth can occur in either of two ways:
Primary growth is characterized by cell division followed by cell enlargement. Primary growth results in the proliferation and lengthening of shoots and roots. All seed plants have a primary plant body, which consists of all the nonwoody parts of the plant. Many herbaceous plants consist entirely of a primary plant body.
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Secondary growth increases plant thickness. Woody plants, such as trees and shrubs, have a secondary plant body consisting of wood and bark. As the tissues of the secondary plant body are laid down, the stems and roots thicken.