Tracheid is Xylem One of the transport structure. The xylem tracheids with conducting water, minerals and support functions, but not with perforation of the tubular cells.

Tracheid function

From the evolutionary perspective, the more primitive tracheids, catheter A molecule is made up of tracheid evolved, but also have the data to show that vessel elements may be different from the plant groups evolved independently. Tracheid tubular cells end sharp, more on the wall Pit . Like vessel elements, tracheids mature for free Protoplast The existence of dead cells. On the wall with different degrees of secondary thickening, but overlapping arrangement, so has the support function.

Tracheid Morphological character

Is a wall thickened elongated, non living cells. Sharp ends, long spindle shape, the diameter is small, the protoplast has disappeared in mature, only Lignification Cell wall thickening, often forming a ring, thread, and other types of scalariform pits. Between the tracheid length ranged from 0.1 mm to several centimeters long, generally 1 to 2 cm. The tracheid overlapped with the two ends of the oblique interpenetration and connection, only through the water solution on the side wall of the thickened part or not Pit Communicate with each other, as their migration ability catheter But, the mechanical support ability.
The difference is that with catheter tracheids into single cells, the end wall without perforation. The longitudinal connection in organs, each other can not through the water and dissolved inorganic salts in which the only through the wall Pit From one cell to another cell, the transporting efficiency is far better than the catheter. The tracheid exists in all Tracheophyte ( Fern , Gymnosperms and Angiosperm ), but does not play a major role in angiosperms, in most ferns and gymnosperms, structure conducting water and inorganic salt only.

Tracheid classification

According to the Lignification The formation of thickened pattern style, can be divided into ring tracheid, tracheid thread, scalariform tracheid, tracheid hole and reticulated tracheid type etc..

Tracheid application

The tracheid in most ferns and gymnosperms, is the only transportation structure, in most angiosperms, tracheid and catheter can exist in the Xylem In.
Among angiosperms, gymnosperms and ferns only tracheids without catheter, and most angiosperms is both. Tracheid cells were spindle shaped, i.e. tapering, the expansion of the middle. The life history and the catheter similar, initially living cells, then the cytoplasmic dissociation of cell death. The cell wall will appear wood thickening, pit pit membrane with high permeability. Typical gymnosperms Bordered pit . The water flow can be regulated by torns activities. In the more primitive plants, tracheids with transport and support functions.