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This is the only type of xylem found in the earliest vascular plants, and this type of cell continues to be found in the protoxylem (first-formed xylem) of all living groups of vascular plants. Several groups of plants later developed pitted tracheid cells independently through convergent evolution .
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue: the vascular cambium and the cork cambium.
A vessel element or vessel member (also called a xylem vessel) [1] is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are found in most angiosperms ( flowering plants ) and in some gymnosperms such as cycads and Ephedra , but absent in conifers .
Both these tissues are present in a vascular bundle, which in addition will include supporting and protective tissues. There is also a tissue between xylem and phloem, which is the cambium. The xylem typically lies towards the axis with phloem positioned away from the axis . In a stem or root this means that the xylem is closer to the centre of ...
Animal tissues are grouped into four basic types: connective, muscle, nervous, and epithelial. [4] Collections of tissues joined in units to serve a common function compose organs. While most animals can generally be considered to contain the four tissue types, the manifestation of these tissues can differ depending on the type of organism.
Tracheids were the main conductive cells found in early vascular plants. In the first 140–150 million years of vascular plant evolution, tracheids were the only type of conductive cells found in fossils of plant xylem tissues. [5] Ancestral tracheids did not contribute significantly to structural support, as can be seen in extant ferns. [6]
Xylem is the water-conducting tissue, and the secondary xylem provides the raw material for the forest products industry. [25] Xylem and phloem tissues each play a part in the conduction processes within plants. Sugars are conveyed throughout the plant in the phloem; water and other nutrients pass through the xylem.
Like all vascular plants, trees use two vascular tissues for transportation of water and nutrients: the xylem (also known as the wood) and the phloem (the innermost layer of the bark). Girdling results in the removal of the phloem, and death occurs from the inability of the leaves to transport sugars (primarily sucrose) to the roots.