Roots play a vital role in plants, which is to take up water and nutrients from the soil.
The first root of a plant that develops from the embryo is called the primary root. In most dicots, the primary root is called the taproot. This main root grows downward and gives rise to branch roots (lateral roots). Most monocots have a fibrous root system, in which no root is more prominent than the others.
Plant tissues develop from specific layers of the embryo just as animal cells do, although the names of the layers are different. The undifferentiated plant tissue from which new cells arise is called the meristem. The apical meristem is found in the tips of developing roots and shoots. Lateral meristems give rise to secondary tissue. Within the apical meristem, certain areas develop into different tissues, as shown below in a Zea mays (corn) root tip. The root cap is a protective structure that is continuously being sloughed off and replaced.
For descriptions of all cell types and their functions, click here.
Note: You can identify various tissues by scrolling over the region with your mouse.
Procambium produces the vascular tissue
Ground meristem produces the ground tissue (cortex and pith)
Protoderm produces the epidermis
This is a cross-section of a Ranunculus (buttercup) root. Note the outer epidermis, large cortex, and vascular cylinder in the center. This particular root has a pentarch (5-arm) pattern of xylem in the center, which can be more clearly seen in the picture below. Surrounding the vascular cylinder (the innermost layer of the cortex), there is a single layer of cells. This layer is called the endodermis (seen below as a red-stained ring of cells), and it functions in protection and regulation of water movement in the root. Endodermal cells have Casparian strips within their walls, which contain suberin and lignin. Note the large amount of starch present in the cortex of this root section.
Below is a picture of a Smilax (greenbrier) root. Note the distinctive endodermis. The outermost layer of the cortex is differentiated as an exodermis, similar in appearance and function to the endodermis.
Lateral (branch) roots arise from a particular region of the root known as the pericycle. This is the layer of cells that surrounds the vascular tissue.
Part of the reason that plants are so successful at absorbing water from the soil is the presence of root hairs. Root hairs make roots appear fuzzy or hairy. They function to greatly increase the surface area available for water uptake. Below is a picture of root hairs on a wheat plant.
