This is a part of the root mantle of Psaronius from Chemnitz
(width 2.5 cm). The little stars are the xylem strands in the rootlets.
In most cases the softer tissue has decayed and been replaced by agate. The
root mantle consists of an inner zone and a outer one. The space between
the roots in the inner zone is filled in with thin-walled tissue, parenchyma.
The roots in the outer zone lie separate.
The roots have a star-shaped xylem strand. This star-shape can be explained
as follows:
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The first wood vessels (the protoxylem) developed in 5 to 9 points
(A to H) lying in a circle around the centre of the root. These wood vessels
were very thin. Then bigger wood vessels began to develop in the direction
of the center (the metaxylem). A star-shaped bundle of wood vessels was the result. A longitudinal section shows that these wood vessels possessed ladder-like thickenings in de walls. Click the slide below to see such a longitudinal section. In the picture to the left the phloem has also been preserved.
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