The stem is among the flowering plants, shaft, usually air, extending the root and have the buds and leaves. Usually branches in various fields.
root is distinguished by the presence of knots that are inserted in the auxiliary buds and leaves, by the absence of terminal cap and its structure. The transition between root and shoot is done in the "neck." There may be underground stems and aerial roots there.
On the mode of growth and branching, the stem determines the size of the plant also has a supporting role in the plant and transport of nutrients between roots and leaves.
A stalk is composed two main areas:
Cross section of a flax stem. 1-core 2-protoxylem 3-4-primary xylem phloem sclerenchyma fibers 5-6-7-epidermisLa bark bark bark
comprises a lining of primary origin: the epidermis. The latter is composed of a single layer of cells lined up next to each other, you can see the occasional stomata to allow gas exchange between the external environment and the stem.
Under the epidermis is the cortical parenchyma, a tissue composed of cells thicker and less organized. It is where photosynthesis takes place and can serve as backup to the plant. Often lignified parenchyma below that serves as support to the plant, is the sclerenchyma.
central cylinder
The boundary between the cortex and central cylinder is bounded by the conductor axes. The latter are found in other parenchymal called medullary parenchyma. The beams are composed of two types of vessels, the xylem and phloem sap xylem conducts water and made crude minerals from the roots to the photosynthetic organs where the sap is sugar load. Then becomes elaborated sap which is driven by the phloem to the bodies energy demand, such as buds, roots, tubers, flowers, fruits ...
In the center of the stem is the pith or medulla containing parenchymal reserve. Among the Poaceae (grasses), this area is replaced by a central vacuum. This explains why the wheat stem is hollow when cut
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