Plant stems function in miscellaneous capacities, mainly in nutrient transport and physical support. The vascular mechanism of plants, finish with xylem and also phloem, filling both purposes. Stems, in addition to roots, also store food because that the plant. Pith, a tissue that lies in the facility of the stem (or, together it is called in trees, the trunk), is responsible for some nutrient storage together well.

Transport

The vascular mechanism in the stem is consistent with the of the roots, providing basic route for water and also nutrients to flow throughout the tree body. The organization of vascular organization is various for various varieties of plants--from the scattered vascular bundles (containing both xylem and phloem) of monocots come the more orderly ring formation discovered in dicots. This distinction in the organization of the vascular tissues has implications because that the way the plant grows. (For a general discussion of monocots and dicots, watch Plant Classification, Monocots and Plant Classification, Dicots.)

Monocot Stems

In monocots, xylem and also phloem are arranged in vascular bundles scattered throughout the stem. Together the plant grows, monocot tribe generate new vascular bundles because that the new tissue. Monocot tribe in basic possess a simpler setup than that uncovered in dicots; the main aspects of the stem are simply the vascular bundles and the pith (used because that nutrient storage) that surrounds them.

Dicot Stems

The vascular system discovered in dicots is rather more complex than that found in monocots. In the dicot stem, the vascular bundles are arranged in a ring, through pith concentrated at the core of the stem, fairly than gift scattered throughout the plant interior. In every vascular bundle, the xylem and also phloem are separated through a substance dubbed vascular cambium. Together the tree grows, existing bundles prosper larger (rather than new vascular bundles gift generated, together in monocots). The vascular cambium operates through producing new xylem and phloem cells, which subsequently pushes the old cell outward and forces the bundle to grow.

Within the course of plants known as dicots, herbaceous dicots and also woody dicots have different arrangements of vascular tissues. In herbaceous dicots (plants, mostly annuals, through soft, non-woody stems), vascular tissue remains in discrete bundles also at maturity. In contrast, when mature woody dicots (plants, greatly perennials, through woody stems) reach maturity, the vascular bundles sign up with together come form continuous rings approximately the interior of the stem. In addition, woody dicots build a lateral mechanism of nutrient move in which vessels referred to as rays extend horizontally native the phloem come the pith, moving nutrients to the pith for storage or come the phloem because that dispersal.

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Figure %: Stem Cross-Sections

Support

In addition to distributing nutrients, vascular organization also administer structural support. In fact, the material commonly known as "wood" is in reality xylem. After ~ a time, the xylem in ~ the center of older tree (woody dicots) ceases to duty in transport and takes ~ above a completely supportive role; this nonfunctioning xylem is referred to as heartwood.


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The newer xylem closer come the surface remains active in the vascular system, and is called sapwood.