Complex tissues are

Explanation

Tissues which are made up of more than one type of cells and work together as a unit are called complex tissues. They are of two types namely xylem and phloem .
Xylem : It is a conducting tissue , helps in conduction of water and minerals form roots to stem and leaves .It is composed of four elements namely tracheids , vessels ,xylem fibres and xylem parenchyma.
Tracheids are elongated or tube like cells with thick and ligngified walls and tapered ends . These are dead and are without protoplasm .Vessels are long cylindrical tube like structures , made of many cells with lignified walls and a large central cavity . Vessels are interconnected through perforations in their walls . They are also dead cells . Both tracheids and vessels are the main water transporting channels .Xylem fibres are long , with thick walls and narrow lumens , gives mechanical strength , xylem parenchyma cells are living and thin walled cells, made up of cellulose . They store food materials in the form of starch of fat.
Phloem : it is complex tissue , helps in conduction of food materials .It is composed of sieve tube elements , companion cells , phloem parenchyma and phloem fibres . Sieve tube elements are long tube like structures and are associated with companion cells . Their end walls are performated in a sieve like manner to form the sleve plates . A mature sleve element shows a peripheral cytoplasm and a large vacuole but lacks a nucleus . The companion cells are specialised parenchymatous cells which are connected to sleve tube by pit fields the companion cells help in maintaining the pressure gradient in the sleve tubes .
Phloem parenchyma is made up of cylindrical cells which have dense cytoplasm and nucleus . The cell wall is composed of cellulose and has pits . It stores food material and other substances like resins . Latex and Mucilage , Phloem fibres are long elongated unbranched cells with pointed apices . The cell wall is thick and is made up of lignin. Phloem fibres of jute flax and hemp are used commerically .