Tissues are the group of cells that are present together to perform a specific function. The tissues are responsible for the growth of the plant. Two types of growth are present in plants. They are primary growth and secondary growth. To study the secondary growth we need to understand the growth ring pant anatomy. The plants that show secondary growth have the presence of growth rings on them. These are derived from the secondary tissues of the plant. Permanent tissues are then formed from these secondary tissues.
The parenchyma is a simple permanent tissue. It is present in almost all the organs of the plant. It is present in roots, leaves, shoots, buds, and almost each and every organ. The parenchyma is responsible for forming up the main bulk of the plant body. The cells of the parenchyma are known as parenchymatous cells. No protoplasm is present in these cells. They are known as living cells. Isodiametric cells are seen in the parenchyma. This means that these cells have equal diameters. The cells can be in the shape of spherical, oval, or round. These are marked by the presence of thin walls. Cellulose is mainly deposited in the cell wall of parenchymatous cells. There are no intercellular spaces present inside the parenchymatous cells. They help in avoiding the defoliation process. Defoliation is the process by which black spots are developed on the surface of leaves. When defoliation occurs, the leaves start to fall off from the plant. Nectar and oil are secreted by the parenchymatous cells and these are released by the plant body also. The parenchyma plays a major role in the storage of food. They help in storing carbohydrates and proteins. The parenchyma tissues also help in the process of photosynthesis.
In the secondary growth of plants, the growth ring plant anatomy plays an important role. They are also known as cambial rings. The vascular bundles start to get themselves arranged in a ring-like manner. They are open in dicot plants. The term “open” means that the cambium is open to growth in these tissues. The cambium grows and then helps in developing the secondary tissues. In the young stages, these rings are present in patches but at the later stages of life, they are present in a continuous form. There are medullary rays that are present between the vascular bundles. These cells are dedifferentiated and by this process, they help in forming the secondary tissues. The growth ring or the vascular cambium is formed by the intrafascicular and interfascicular cambium. This growth ring then becomes active and then they begin to divide and form new cells. These new cells are formed both inside and outside with the help of periclinal divisions. These growth rings are more active on the inner side as compared to the outer side. Towards the periphery, there is an expansion of the cambium rings. The primary xylem is kept intact and there is an amount of increase in the secondary xylem. Due to this increase in the amount of xylem, the amounts of phloem keeps on crushing.
The activity of these rings is affected by the different temperatures of the year. Mainly in Asia and Central North America continent, we see a difference in temperature so we observe that the growth of the cambium rings is affected. These cambium rings are very active in the month of the spring season. There is an increase in the rate of transpiration and due to this a large amount of water is needed for the growth. These vessels are generally produced with large amounts of lumens. In the winter season, we see the opposite of this happening. In the Winter season, the growth of the cambium ring is slowed down. This is because the cambium is less active in the month of winters. The wood that is formed in the spring season is known as springwood and the wood that is formed in the winter season is known as autumn wood. The springwood is low in density and also light in colour whereas the autumn wood has high density and is dark in colour. The number of rings in the trees helps in determining the age of the tree. The tree that has more number rings means that it is more in age. This study of rings and then determining the age of the plant is known as dendrochronology. These rings are more often seen in trees that grow in temperate regions. The regions that have uniform temperature and rain do not show these cambial rings. Due to constant temperature, we see no activity of the cambium so no rings are formed in this case.
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1. What are the Functions of the Epidermal Tissue System?
Answer: The functions of the epidermal tissue system are:
Protection: They help in providing protection to the plant from external injuries. Also, they help to avoid the excess of evaporation and also give protection from solar radiation.
They help in the absorption of water and minerals with the help of root hairs.
They help in the exchange of gases with the help of stomata.
They help in controlling the process of transpiration with the help of cuticles and trichomes.
With the help of trichomes, many sticky substances are secreted.
2. What are Xylem Fibers and Xylem Parenchyma?
Answer: The xylem fibers are sclerenchymatous in nature. They are of long and narrow nature. On both ends, tapering is present. Their walls are highly lignified. Central lumens are also present in them. As they have very thick walls so no spaces are present in them. Septate and aseptate are the two types of fibers that are present. They help in providing mechanical strength and support to the plant. They are present in all vascular plants. The xylem parenchyma is living in nature. They are also thin-walled. Cellulose is present in their cell walls. They are marked by the presence of a prominent nucleus and a dense cytoplasm. They are also present in all vascular plants. They help in the storage of food and also reserve food materials. The reserve food materials can be starch and fats. Tannins are also present in them. Water is conducted by radial conduction inside them.