Vessel element

The term refers to the trachea in botany, a vessel elements of the xylem, which is located in the vascular bundles of the stem axis of higher plants. Angiosperm seed plants transported in the xylem water from the roots to the leaves. The main driving force for this is the transpiration, which is explained by the cohesion theory. In addition, the root pressure can play a role, such as in the spring. Xylem tracheids are like dead, lignified cells.

In xylem cell walls in the axial direction are resolved completely or partially. Within a vessel more tracheal are interconnected so that in comparison to tracheids a long continuous pipe is made. The totality of the tracheae form (together with the tracheids ) thus provides a continuous and communicating pipe system of the roots to the leaves.

In the transverse direction, a water transport across pits is possible. The pits of angiosperms ( angiosperms ) are simpler than the bordered pits of the torus Margo type of gymnosperms ( gymnosperms ) built. The Tüpfelmembran the trachea consists of a net-like tangled mesh of microfibrils. The very small " mesh " of Tüpfelmembrane prevent the spread of the gas phase in the case of embolism, since the forming menisci can withstand very high pressures on the water-gas limit ( Young-Laplace equation). If the pressure difference between water and gas side is too large, adjacent vessels may also be embolized. A local limit of emboli can therefore be achieved probably better off with bordered pits of gymnosperms, as they function as check valves.

One can distinguish between tracheae and tracheids, by examining a cross-section of a histological preparation on the axial walls of the respective vessels. Tracheae also often have a significantly larger diameter. You are solely responsible for the water line in contrast to the tracheids. Tracheids bear at the same time still for the mechanical stabilization of the plant at (double function). In deciduous trees raise additional wood fiber cells, the mechanical stability. Due to the larger diameter of the flow rate is significantly higher than in tracheids ( Hagen- Poiseuille'sches Act) in tracheae, but the risk of vascular embolism increases by tearing off the water thread. Most gymnosperms ( gymnosperms ) have to carry water only tracheids (except Gnetales ). In contrast, in most angiosperms ( angiosperms ) are both tracheae and tracheids before ( exceptions are eg the Winteraceae and Trochodendraceae that have no tracheae ).