Complex Tissue

Complex tissue: The tissue composed of more than one type of cells is called complex tissue. They conduct water, minerals and prepared food, and this is why they are also called conducting structure of vascular bundle. Xylem: There are two types of xylem: primary and secondary xylem. Xylem developed during primary growth from pro cambium is celled primary growth from vascular cambium is called primary xylem. Secondary xylem is the xylem grown during secondary growth from vascular cambium. Primary xylem comprises prototype  and meta xylem. Meta xylem develops after the prototype but before the secondary growth. Prototype is distinguished by narrower vessel developed from smaller cells but meta xylem cells are usually larger. Different xylem cells are the constituents of xylem fibers. (a) Tracheae: Tracheae are elongated cells with slender and sharp ends. After significations, their lumpen may become narrower, and so in that case transportation of water occurs mainly though the lateral paired pits on their walls. Thickening of walls is of different types, such as, elliptical, spiral, californium, reticulated and pitted. Tracheae occur in ferns and gymnosperms, and also are present in the primary and secondary xylem of angiosperms. Its main function is  to provide sap conduction-related organ with proper rigidity. Sometimes they also story food.