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 RootsThe root is one of the first parts of a plant that starts to grow. A primary root develops from a plant's seed and quickly produces branches called secondary roots. At the tip of each root is a rootcap that protects the delicate tip as it pushes through the soil. Threadlike root hairs grow farther back on the root. These hairs greatly increase the plant's ability to absorb water and minerals from the soil. Kinds of Roots There are two main kinds of root systems -- fibrous and taproot. Grass is an example of a plant with a fibrous root system. It has many slender roots of about the same size that spread out in all directions. A plant with a taproot system has one root that is larger than the rest. Carrots and radishes have taproots. Taproots grow straight down, some as deep as 15 feet.
The Root Tip. A root grows in length from an area at its apex (tip). This growth area is called the apical meristem. A meristem is any part of a plant where the cells divide rapidly, forming new cells continually. The apical meristem is covered by the root cap, a thimble-shaped group of cells. The root cap protects the delicate root tip from damage as the root grows in length and the tip pushes through the soil. The cells produced by the apical meristem are all small and nearly identical. In the region of elongation, the cells rapidly grow longer. Farther back lies the region of maturation, where the cells differentiate -- that is, take on a different structure and appearance according to their functions in the mature root. The Outer Tissues. The outer layer of cells of a root is called the epidermis. It serves as a sort of skin and protects the tissues beneath. Tiny, hairlike extensions called root hairs grow from the epidermis. The root hairs absorb most of the water and minerals that a plant takes in from the soil. A thick layer of rounded cells called the cortex lies just inside the epidermis. These cells contain stored food and water. The inner layer of cells of the cortex make up the endodermis.
Secondary Tissues. All the tissues described above are known as primary tissues. Many plants that live just one year have only primary tissues in their roots. But other plants, especially those that live more than one year, have secondary tissues in their roots in addition to primary tissues. The growth of primary tissue adds to the length of a root. The development of secondary tissue adds to its thickness. Secondary-tissue growth produces the large, brown, woody roots in trees, shrubs, and other plants that live for many years. Secondary tissues develop from two meristems. One, called the cork cambium, originates beneath the epidermis, generally in the pericycle. It produces cork cells and pushes them toward the outside of the root. As the cork expands outward, the endodermis, cortex, and epidermis die and peel off. The cork replaces them and becomes the outer covering of the root. The other secondary meristem, the cambium, lies between the primary xylem and the primary phloem. It produces secondary xylem cells toward the center of the root, and secondary phloem cells toward the outside. Questions or comments about this page?
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Some plants have modified
roots that perform special functions. Roots that grow
from the stem above the ground are called adventitious
roots. They include the prop roots of corn
and certain other plants. Prop roots grow down into the
soil from the lower part of the 
Parts
of a Root
The Core,
or stele, is the central portion of the root.
Its outer layer of cells is called the pericycle.
Inside the pericycle are two kinds of tissues, xylem
and phloem. Xylem includes rows of dead, tubular
cells called vessels, which conduct water and
minerals up to the stem and 