Root Directory
Root
Anatomy- Apical Meristems
Root Directory
Root anatomy is very simple. The root is composed of three concentric circles of primary tissues. The central core is Vascular Tissue. This central core of cells is derived from the Procambium and is called the Stele. This is surrounded by a ring of Ground Tissue (Cortex) which is covered by an Epidermis. These can be readily traced back to an Apical Meristem. However, the Root Apical Meristem (RAM) is covered by a Root Cap.
Think of the root as being composed of a cap and a body.
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The Root Apical Meristem produces the three primary meristems (procambium - ground meristem & protoderm) plus the root cap. In cases wherein the root cap has a separate primary meristem, it is called the Calyptrogen. This occurs in roots that have distinct Initials for the tissues of the Root Body.
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| Dividing Apical Cell in Equisetum (horsetail). Note the Large Apical Cell caught in mitosis. All cells in the organ can be traced back to this cell. |
The Apical meristems of seed plants are multicellular but there appear to be cells analogous to Apical Cells in the roots of some species like corn. These are called Initials.
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Banana Root Apex - High Magnification - Locate the Cap and the Body - Follow the cell files in the body towards the RAM - Are Initials Present? |
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Banana RAM - Higher Magnification - The three layers of the body converge on a few "Initial Cells". The Root Cap has a distinctly separate origin (Calyptrogen). However, that is not as clear as it could be in this specimen. |
Apical Cells are not found in seed plants but all the cells in the body of some roots can be traced back to a few apical cell-like "Initials". Cell files converge upon these and they bear a resemblance to apices which have an apical cell. The Root Cap of these roots appears to have a separate origin from the cells of the body. A distinct boundary can be seen between the Root Cap and Body of these RAMs. The Root Cap can be readily plucked from the body. This trait was used to devise some imaginative experiments on the root cap and geotropism.
| Root Apices of Hyacinth | |
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