Stele (biology)

As a stele (Greek στήλη " pillar") the whole of the primary vascular tissue is referred to in botany. It can (after Strasburger, 35th ed ) eight stelae types are distinguished.

Steles types

  • Protostele: The set of pathways is limited to a single ( central ) concentric vascular bundles. There are both types in which the xylem and phloem outside inward is ( perixylematisch ), and the other way around ( periphloematisch ). Probably this is the most original form, it was typical of the first land plants (eg Urfarne ), but is still present in some young forms of ferns.
  • Aktinostele: Single central vascular bundle, which is located inside the xylem and star-shaped in cross-section (Greek ακτινοτός " surrounded by rays" ). The phloem fills in a sense the ' jet spaces ' of the ' Xylemsterns ' from. Even before she came in Urfarnen. It is particularly prevalent today in the fork blade and the plants Bärlappgewächsen. In addition, you will find this type in root in the form of the central cylinder.
  • Plektostele: (Greek πλεκτός " braided" ) is understood as a transitional form to the next guy. It does not (yet ) of a central undivided Leitgewebestrang, but the (already ) having a plurality of separate xylem and Phloembereiche. This is the most common type in lycopods.
  • Polystele: A plurality of concentric axially parallel vascular bundles, which are distributed over the entire cross-section of rung. It is based on a phylogenetic development of the aktinostele by fracturing.
  • Siphonostele: Tubular Leitbündelstrang (Greek σίφον "tube" ) which surrounds the marrow. Occur on limited gaps in the hose to the attachment points for leaves. This is the stele type some fern families.
  • Dictyostele: The siphonostele very similar. In contrast, here is not a closed tube before, but a tubular network. (Greek δίκτυον " network "). Sometimes the term is shell and tube for this typical for most ferns stelae type used. Each vascular bundle is concentrically surrounded by a pericycle and endodermis one.
  • Eustele: stelae type of dicotyledons. The collateral vascular bundles are usually fused into a cylinder (especially in trees ), and (only ) separated by wooden beams. So this stele type actually corresponds to a single concentric vascular bundles ( cf. protostele ) with included cord.
  • Ataktostele: (Greek άτακτος "disordered " ) stelae type in monocots. The closed collateral vascular bundles are irregularly over the stem axis cross-section distributed (see Polystele ), the Xylempole of the vascular bundles, however, are always directed towards the center of the stem axis cross-section. For this reason, it is also of a single concentric vascular bundles from the starting shape. That part of a comprehensive stele tissue sheath is indicated, supports this assumption.
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