rootov.htm

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Roots-An Overview

We saw a root tip earlier in the unit on apical meristems. Now we will be looking at some actual microscopic images of monocot and dicot roots cut in cross-section above the meristem region.

You will encounter some familiar terms here that are applied to both root and stem tissues. For example, protoderm, ground meristem, and procambium--the embryonic tissues that differentiated into mature tissues of stems-are also found in roots.

In roots, vascular tissues are arranged differently than in the stem and there will always be an endodermis with a Casparian strip. Watch for differences in the monocot and dicot roots. One key difference involves location of the vascular tissues. In this diagram of a dicot root, note how the procambium is shown central to other tissues. In the mature dicot root, xylem and phloem are found centrally placed. In a monocot root, xylem and phloem tissues are arranged in a ring.

Now, roll over the top-most root hair on the right.

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Endodermis and the Casparian Strip

One of the diagnostic features you should watch for in roots is the endodermis with its Casparian strip. If present, you are looking at a root rather than a stem.

The vascular tissues, xylem and phloem, are always found within the endodermis of the root. The endodermis determines what moves into the vascular tissues by exerting cellular control over symplastic transport. Note how the Casparian strip prevents apoplastic transport within the root!

The xerophytic leaf of the pine possesses an endodermal layer so do not assume that endodermal tissues are unique to roots. They are, however, typical and obvious in roots.

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