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Plant Tissue Systems


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Vascular Tissue System
Plant Vascular Tissue

Plant Vascular Tissue: Xylem and Phloem

Image copyright: Dave Webb

Plant Tissue Systems: Vascular Tissue

Xylem and phloem throughout the plant make up the vascular tissue system. They allow water and other nutrients to be transported throughout the plant. Xylem is consists of two types of cells known as tracheids and vessel elements. Tracheids and vessel elements form tube-shaped structures that provide pathways for water and minerals to travel from the roots to the leaves. While tracheids are found in all vascular plants, vessels are found only in angiosperms.

Phloem is composed mostly of cells called sieve-tube cells and companion cells. These cells assist in the transport of sugar and nutrients produced during photosynthesis from the leaves to other parts of the plant. While tracheid cells are nonliving, sieve-tube and companion cells of the phloem are living. Companion cells possess a nucleus and actively transport sugar into and out of sieve-tubes.

Plant Tissue Systems: Plant Growth

Areas within a plant that are capable of growth via mitosis are called meristems. Plants undergo two types of growth, primary and/or secondary growth. In primary growth, plant stems and roots elongate by cell enlargement as opposed to new cell production. Primary growth occurs in areas called apical meristems. This type of growth allows plants to increase in length and to extend roots deeper into the soil. All plants undergo primary growth. Plants that undergo secondary growth, such as trees, have lateral meristems that produce new cells. These new cells increase the thickness of stems and roots. Lateral meristems consist of the vascular cambium and the cork cambium. It is the vascular cambium that is responsible for producing xylem and phloem cells. The cork cambium is formed in mature plants and yields bark.
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