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Roots, Stems & Steles

Stele - Description of Vascular Tissues which develop from Procambium

Everyting inside the Endodermis


Proto means first. Protosteles are relatively simple, and have been observed in the oldest fossil plants. Consequently, they represent the first steles.

The simplest protostele is the Haplostele. This consists of a solid core of xylem surrounded by a layer of Phloem. An Endodermis surrounds the stele.

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Haplostele - What is the Pattern of Xylem Maturation?

Psilotum Rhizome Cross-Section
RhizoneX-S240Lab.jpg (133769 bytes)RhizomeStele240Lab.jpg (21842 bytes)

The Stele occupies a central region in the Psilotum Rhizome. Xylem is found in the center of the Stele.This is an example of a Haplostele. The Xylem stains Red because its walls contain Lignin. Lignin makes the walls water-proof and it add strength to them.  It is surrounded by Phloem which stains Blue. The Endodermis is hard to see in this photo. You need a Ph. D. to see it!

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The Endodermis is clearly visible in this Stele. Its cell walls have become heavily impregnated with Lignin and are relatively thick. Xylem occupies the center but the Phloem occupies indentations in the Xylem. This makes the Xylem resemble a Star. Consequently this is called an Actinostele. Actino menas Star.

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Cross-section of a Psilotum Stem with an Actinostele

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Same as Above but seen with Polarized Light The Star-like quality of the Xylem is more apparent in this image.


The xylem appears to be dissected into plate-like sectors in a Plectostele. Phloem surrounds the xylem. An Endodermis surrounds the entire stele.

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Plectostele from Lycopodium


A Siphonostele has a pith in the center.

An Ectophloic Siphonostele has Phloem on its exterior circumference.

An Amphiphloic Siphonostele has Phloem on both sides of the Xylem.

An Endodermis is typically present. on both sides of the stele

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Amphiphloic Siphonostele

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Ectophloic Siphonostele


A dictyostele is essentially a divided Amphiphloic Siphonostele. The Stele consists of Individual Bundles of Vascular Tissue.These contain a central strand of xylem surrounded by Phloem with an Endodermis surrounding the bundle. The   bundles are arranged in one circle around the axis.

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Fern Dictyostele


Eustele is similar to the dictyostele except that the bundles lack an endodermis and are collateral. Collateral  Bundles have xylem on one side and phloem on the other, and the absence of an Endodermis. The bundles are arranged in one circle around the axis.A Eustele is characteristic for Dicot Stems.

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Eustele of Aristolochia


An Atactostele consists of collateral bundles distributed in more that one ring within the Stem. This does not mean that the bundles are randomly arranged. A complex organizational pattern is present, but it is not obvious to a casual observer. A Pith is not present. There is no Endodermis. This stele is typical for Monocots like Sugarcane.

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Asparagus Stem

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Asparagus Vascular Bundle

Name That Stele

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Corn Stem

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Plant X

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Sugar Cane Section

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Negative Image of Sugar Cane Stem

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Makaloa Cyperus laevigatus Stem

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Makaloa Vascular Bundles Dicot or Monocot?

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Corn (Zea mays) Root

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Corn Root with High Magnification - Locate the Endodermis

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Clover (Trifolium) Stem

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Clintonia (Liliaceae) Root

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Note the interconnection of Bundles to form a Network

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