Xylem

plants (ferns and seed plants), water and inorgic salts are mainly transported, and there are complex
tissues that support the
. The woody part is combined with the ligament to form a continuous tube system in the plant. The woody part consists of catheters, tube cells, wood fibers, and thin-walled tissue cells. A catheter is a string of highly specialized tube cells whose cell end walls are connected by perforations, each of which is called a catheter molecule or catheter joint. Catheter molecules are living cells in the early stages of development, and when matured, protosites disintegate and cells die. In the process of maturation, the cell wall wood, and has rings, threads, ladders, mesh and holes and other forms of secondary thickening. At the end wall between two adjacent catheter molecules, a perforated plate is formed after dissolution. The formation of perforation makes the cross wall in the catheter open and become a connected pipe, the length of each catheter can be from a few centimeters to about 1
meters; Tube cells are a non-perforated narrow tube-like molecule, with the ends becoming sharper, the cell walls significantly thickened, and woody, and the cells die after maturation. No perforation is formed between the two tube cells, but is connected by a trie on the cell wall. Cell calibre is small, the ability to conduct water is much smaller than the catheter. It is the main water transport organization of naked plants. Most of the bee plants, tubes and catheters can be present in the same plant. The main functions of the tube cells are water transmission and inorder salt, and have a supportive effect. Wood fibers are thick-walled tissue cells that are increasingly sharp at both ends of the long shape and act as a support. Wood thin-walled tissue cells are living tissues, mainly playing a storage role. When the cells mature, they generally have thickened secondary walls and woody. The woody part is the result of the formation layer activity of the tube, and the woody gemal leaf plant and the naked plant continuously produce new wood parts to form useful wood due to the activity of the formation layer.

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