Vascular bundle

Vascular bundles ( fascicles ) are designed for long-distance transport of water, solutes and organic substances ( assimilates, mainly sugar) in the shoot, responsible in the journal and in the roots of higher plants ( vascular plants ). Vascular bundles consist of xylem (wood part ) with cell elements for water transport (for example, tracheae and tracheids ) and the phloem ( bast, sieve ) for the transport of assimilates with sieve or sieve tubes and companion cells.

Leitbündeltypen

There are several Leitbündeltypen:

• Simple vascular bundles consist of a sieve or piece of wood.
• Composite vascular bundles have a sieve and a piece of wood.
• For concentric vascular bundles of phloem is to the wood part ( periphloematische vascular bundles ), or the piece of wood is around the phloem ( vascular bundles perixylematische ).
• The most common type is the so-called collateral vascular bundle in which the phloem the wood part is opposite ( the Xylempol is the branch axle center facing ).

• For open collateral vascular bundles still occurs, add a cambium between the xylem and phloem. This arrangement occurs in dicotyledonous ( dicot ) plants.
• When closed collateral vascular bundles lack the cambium and the vascular bundles are surrounded by a closed, sclerenchymatous Leitbündelscheide. This arrangement occurs in monocotyledons ( monocots ) or ( other ) herbaceous plants.

• A special form of collateral type is the bikollaterale vascular bundles, as occurs for example in the Cucurbitaceae and Solanaceae. Here is another Phloemteil is added to the vascular bundles in the stem axis mid -facing side.
• In roots, the vascular bundles are combined to form a radial vascular bundles, where the wood part like the spokes of a wheel is arranged - the bast part is between the spokes ( aktinostele ).

Longitudinal section through a vascular tissue of Zea mays

Open, bikollaterales vascular bundles in Cucurbita pepo

Radiäres vascular bundles in Iris Germanicae