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# SRM - 1 - Vascular System in Plants ## Introduction - Vascular system in plants is an arrangement of complex interconnected tissues and associated cells - These connected tissues are also called vascular tissue, and hence the name ‘vascular system’. This system helps water to move up the plant ag...

# SRM - 1 - Vascular System in Plants ## Introduction - Vascular system in plants is an arrangement of complex interconnected tissues and associated cells - These connected tissues are also called vascular tissue, and hence the name ‘vascular system’. This system helps water to move up the plant against gravity. - Let us discuss various types of vascular tissues found in the vascular system ### Xylem - The word xylem is derived from the Greek word ‘xylon’ meaning ‘wood’. - The term ‘xylem’ was first introduced in 1838 by the Swiss Botanist, Carl Nageli. It is a plant vascular tissue, which transports water and dissolved minerals from the roots to the rest of the plant. Since, the transport of water is always unidirectional, i.e. from the bottom to the top of the plant. - Xylem tissues consist of various specialized water-conducting cells, which are known as tracheary elements. Xylem trachery elements comprise of cells known as tracheids and xylem vessels, both of which are narrow, hollow, and elongated cells. - **Tracheids are the dead cells of the xylem tissue. These are less specialized as compared to xylem vessels. Water moves from one tracheid to another through a thin perforated cell wall called the ‘pit’.** - **Xylem vessels are the main cells which conduct water. In angiosperms (flowering plants). These are dead cells, yet water flows relatively unobstructed from one xylem vessel to another through perforations, known as pits**. - Along with the tracheary elements, xylem tissue also contains xylem fibres and xylem parenchyma. - Xylem fibres are more non-living cells meant for providing support to the plant body. These cells are usually present between tracheids and xylem vessels. - **Xylem parenchyma are thin-walled unspecialized cells for the storage of various substances. These are the only living cells of the xylem tissues**. #### Formation of Xylem - The formation of xylem starts when primary cells called ‘primary xylem’ arise from the actively dividing cells of growing root and shoot tips. - Woody plants have ‘secondary xylem’ which forms the major part of a mature stem or root. These are formed as the plant expands in girth and builds a ring of new xylem around the primary xylem tissues. - During this process, the primary xylem cells die and lose their function of conducting water and minerals; thereby, forming a hard skeleton that supports the plant body. - Therefore, in a tree, only older cells of the trunk and the secondary xylem (also known as ‘wood’), can conduct water, whereas the inner part (known as ‘heartwood’) comprises of dead but strong primary xylem. - It is important to note that the age of a tree may be determined by counting the number of annual xylem rings which form at the base of the trunk. ### Phloem - The term ‘phloem’ is derived from the Greek word “phloos", meaning ‘bark’. This term was first introduced in 1838 by Carl Nageli. Phloem, also known as bast, is a type of vascular tissue which is responsible for the conduction of foods prepared in the leaves to all other parts of the plant. - This food made in the leaves is transported in the form of soluble organic compounds. Since, food is synthesized by all the green part of the plant, the direction of flow of phloem is bidirection, i.e. given both leaves to all parts of the plant, and from other parts such as stem to leaves. - Phloem comprises of various specialized cells. These are sieve tubes, companion cells, phloem parenchyma, phloem fibres and cells. - **Sie