Spring Wood and Autumn Wood
Several environmental and physiological factors are controlling the cambial activity. In the temperate areas, the entire year does not have uniform climatic conditions. In the spring, the cambium will be more active and it produces more amount of xylem elements which constitute vessels that are wide. The wood that is formed in this season is called as spring wood or early wood. In the winter, the cambium is not much active and it forms few xylem elements with narrow vessels. This type of wood is known as autumn wood or late wood.
The spring wood has light color and has low density while the autumn wood is dark in color and has high density. The concentric rings that are formed by the autumn wood and spring wood alternately are termed as annual rings. When the stem is cut, the annual rings in it will give an indication of the age of the tree.
Heart wood and Sap wood
The innermost layers of the stem in the old trees consist of cells that are filled with certain substances like resins, gums, essential oils, aromatic substances, oils, and tannins. These substances fill up most of the part of secondary xylem. These substances will make the stem durable, hard and resistant to the microbes and insects. The deposition regions of the walls comprise of dead substances and they are lignified. This wood is called as heart wood. The heart wood is known to provide mechanical support to the stem and it will not transfer water from one part of the plant to another. The peripheral regions of the secondary xylem are light in color and those regions are called as sap wood. This woody region will help in water transport as well as transport of minerals from the root to the leaf.
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