COMPLEX TISSUE
Group of more than one type of cells having common origin & working together as a single unit .Types of complex tissue in plants :
1.XYLEM
2.PHLOEM
Together they are called vascular tissue.
Xylem conduct water and minerals from roots to the different parts of plant & PHLOEM transport food from leaves to the different parts of plant.
XYLEM: Introduced by Nageli in 1858. Components of xylem are:
1.Trachieds
2.Vessels
3.Xylem fibres
4.Xylem parenchyma
•TRACHIEDS: These are elongated tube like dead cells without protoplasm having tapering ends .These are long cells but not as long as fibres . Tracheids of primary xylem develop from procambium and that of secondary xylem from vascular cambium.In the beginning these cells possess living protoplasm but due to the deposition of lignin on the walls they become dead at maturity.
Tracheids possess various types of wall thickening which are annular, spiral,scalariform,reticulate and pitted as shown
•Functions of tracheids : 1. Main function is to conduct water and minerals.
2. They provide mechanical support to the tissue.
•VESSELS:These are long tube like structure consisting of drum like cells placed one above the other with perforations (pore) in the end walls.The single vessel is made up of many cells and have a length of 10cm or more.They are dead due to lignification.Vessels of primary xylem develop from procambium and that of secondary xylem from vascular cambium.Vessels possess various types of wall thickening which are annular, spiral,scalariform,reticulate and pitted.
•1.Vessels are the chief conducting tissue in angiosperm for translocation of water and minerals.
•2. They provide mechanical support to the plant.
•XYLEM FIBRES : Develop from meristematic cells having lignified secondary walls & narrow lumen ,they are longer than the tracheids .Their main function is to provide mechanical support.
•XYLEM PARENCHYMA: They are the only living parenchymatous cells in xylem .Their main function is to help in conduction and store food material.They are of two types:
(a)Wood parenchyma that formed from fusiform cambial initials.
(b) Ray parenchyma formed from ray initials of the cambium.
