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Wood is a structural tissue/material found as xylem in the stems ... form thickened secondary cell walls, composed mainly ... water, wood has three main components.
The first lignified secondary walls evolved 430 million years ago, creating the structure necessary for vascular plants. The genes used to form the constituents of secondary cells walls have also been found in Physcomitrella patens. This suggests that a duplication of these genes was the driver of secondary cells wall formation. [2]
There are often pits on the cell walls of tracheids, which allows for water flow between cells. Tracheids are dead at functional maturity and do not have a protoplast. The wood of gymnosperms such as pines and other conifers is mainly composed of tracheids. [2] Tracheids are also the main conductive cells in the primary xylem of ferns. [3]
The major polymers that make up wood (largely secondary cell walls) include: cellulose, 35-50%; xylan, 20-35%, a type of hemicellulose; lignin, 10-25%, a complex phenolic polymer that penetrates the spaces in the cell wall between cellulose, hemicellulose and pectin components, driving out water and strengthening the wall.
The polysaccharide components of plant cell walls are highly hydrophilic and thus permeable to water, whereas lignin is more hydrophobic. The crosslinking of polysaccharides by lignin is an obstacle for water absorption to the cell wall. Thus, lignin makes it possible for the plant's vascular tissue to conduct water efficiently. [15]
Secondary xylem is formed during secondary growth from vascular cambium. Although secondary xylem is also found in members of the gymnosperm groups Gnetophyta and Ginkgophyta and to a lesser extent in members of the Cycadophyta, the two main groups in which secondary xylem can be found are:
Image credits: Amazon MGM Studios Wood’s “battered and bruised body” was reportedly found onshore the next morning near an inflatable dinghy. A “dying” 80-year-old woman who claimed to ...
Wood is primarily composed of xylem cells with cell walls made of cellulose and lignin. Xylem is a vascular tissue which moves water and nutrients from the roots to the leaves. Most woody plants form new layers of woody tissue each year, and so increase their stem diameter from year to year, with new wood deposited on the inner side of a ...