Root Directory
A typical Root BODY can be dividend into the following Zones
Apical
Meristem Zone
Elongation Zone
Differentiation
(Maturation) Zone (Root Hairs Present)
The Apical Meristem is the zone in which cell divisions occur.
These cells Elongate, and subsequently Differentiate into cells and tissues which have mature traits. These intergrade and overlap when all of the tissues are considered but it is possible to locate these in general terms.
Root Hairs develop in the Maturation Zone. They would be destroyed if they differentiated in the Elongation Zone!
Furthermore, the internal tissues of the root are in an optimal state for water uptake and translocation in the Maturation Zone. New Root Hairs are continuously produced as roots grow through the soil.
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| Cross Sections through Pineapple Roots stained with Toluidine Blue: Note the Root Hairs. The Image on the right was viewed through Crossed Polarizers! Pineapple is a MONOCOT! | |
Roots are composed of three concentric rings of tissues. These are vascular, ground & epidermis. This organization is illustrated by Selaginella which is a seedless plant.
It has a solid core of xylem, surrounded by a ring of Phloem which is surrounded by ground tissue (Cortex). The innermost layer of the Cortex is the Endodermis.
An Epidermis is the outermost ring.
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| Cross-Section of a Selaginella root. Locate the concentric circles of tissues. | Center of a Selaginella root with the vascular tissues labeled. |
The classic root which is studied in all Botany courses is that of Ranunculus, a dicot. Its anatomy is identical to Selaginella, except for the fact that the central xylem is star-shaped.
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Cross-Section of Ranunculus Root - Locate the concentric circles of tissues. The vascular tissues are at the bottom center of the image. The densely stained purple cells in the Cortex are Parenchyma that contain many Amyloplasts. Starch storage is one important adaptation of roots. |
Vascular cylinder from a Ranunculus root. The xylem has a star-like appearance. The Phloem occupies the indentations between the xylem arms. The Endodermis is the layer of small cells which surrounds the vascular tissues. Endodermal cells opposite the Phloem have thick lignified Cell Walls while those opposite the xylem do not. |
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| Diagram showing the organization of Vascular Tissues and the Endodermis. |
