Much speaks on behalf of the origin of xylem fibres and wood vessels from the tracheids. Small pieces of wood are covered with a mixture of potassium perchlorate and concentrated nitric acid. The surfaces of the wooden pieces are strongly attacked. The single cells can be scraped off after washing of the preparation and examined under the microscope. Let us start with a portrait of the different cell types .
Tracheids are the chief water-conducting elements in gymnosperms and seedless vascular plants.
They can also be found in angiosperms. Tracheids are elongated cells, closed at both ends. In average are they 1 mm long. They are regarded as the prototype of prosenchymatic cells, since the cell's ends are pointed and real final walls are missing. Tracheids look often square in cross-section, the lignified secondary wall is relatively thin.