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Pterophyta - 2 |
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Leaf Gap: The concept of a leaf gap is important. However, it is a little challenging because you need to think in three dimensions. I am including some drawings by Salvador Vebii who is my favorite surrealist artist.
| A Leaf
Gap is present when a Leaf Trace diverges from
the stele without its immediate replacement by vascular tissue. I have tried to illustrate
this. The illustrated stele is a siphonostele.
Note that the Stele (Dark Green) forms a complete
hollow cylinder below the node. The cylinder is broken
into two crescent-shaped columns near the Node
because some of the vascular tissue has diverged from
the stele. The divergent vascular tissue is the Leaf Trace. The leaf trace enters the base of the petiole and forms the midrib of the leaf. The gap in the stele contains parenchyma cells rather than vascular tissues. This area is called the Leaf Gap because in the absence of a Leaf there would be an unbroken cylinder of Vascular Tissue like that seen above. |
 Cross Section of a Siphonostele through the base of a Node |
| The next two drawings attempt to show the same structures from a 3-D Perspective. I haven't been able to illustrate the connection between the stele at the nodes and the internodal stele below. |  
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| These drawings
are are an attempt to produce a 3-D representation of what
happens to a Single Leaf Trace on one side
of the stem.
The leaf trace is emerging towards you. The stele is re-unified above the node and appears as a complete cylinder as seen in cross section. |
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More Models of the Leaf Gap
This diagram contains two Vascular Bundles running vertically in the stem. These produce 3 branches as they approach a node. One branch diverges into the leaf. It is called a Leaf Trace. The other two Branches diverge
laterally and curve upwards. The Stem Traces merge above the node and reform the vertical Vascular Bundle of the Stem. Imagine that your body is a Vascular Bundle in the stem. Your neck and arms represent the three vascular branches which occur at a node. Your Head will be a Leaf. Place your arms directly over your head so that your palms are together. Allow your neck to go limp so that your head leans forward. Get the Picture!!! This could be the next craze!!!!! |
 Diagram Showing Two Vascular Bundles in a Stem. Note the divergence of the Leaf Trace & the Stem Traces. Locate the leaf Gap.
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| The presence of many overlapping
leaf gaps produces a highly
dissected stele, like a dictyostele
or a eustele. These are composed of many individual Vascular Bundles of different Sizes.
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