Analysis:
In temperate regions, such as North America, North Asia and Europe, trees grow slowly and rapidly, fast in spring, slow in summer and stop growing in winter. This seasonal growth rhythm is repeated once a year, forming annual rings (or rings)-an annular texture that can be clearly seen on any stump. Each round represents a new xylem that grows in a year. Light-colored rings show rapid growth in spring, while dark rings show slow growth in summer and autumn. As the tree grows older, the cells in the long rings gradually lose their activity, and then they are filled with resin, gum and oil to harden them, forming so-called heartwood. The support of trees mainly depends on heartwood, and wood is also heartwood.
The formation of annual rings
The outermost bark of a tree is a protective layer. There is a thin layer next to its interior, and the new bark is completed here. This layer contains vascular bundles and has active phloem layer and xylem layer. The thin phloem layer is often mistaken for a part of bark. Cork cambium is sandwiched between phloem and bark. In addition, there is an invisible vascular cambium, only one cell thick, from which the growth of trunk begins. During the growing season, cambium cells divide constantly. Some of them move to the periphery to become phloem, while others move to the center of the tree to become xylem. The cambium grows rapidly in spring, because trees grow new leaves at that time, so it needs to transport a lot of water and store nutrients. Trees produce larger cells at this time, and the conduits for transporting water between cells are also larger. In summer and autumn, the growth rate slows down and cells shrink. A circle of large cells and a circle of small cells form annual rings together.
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