Monday, February 29, 2016
There are simple and complex tissues in plants. Parenchyma, collenchyma, sclerenchyma, are examples of simple tissues . PlantTissues fall into two large categories: Meristematic, or Permanent (Non-Meristematic)
Xylem and phloem are example for complex tissues. Simple tissues have only one type of cell while complex tissues have several different types of cells.
Parenchyma: parenchyma is the fundamental and simple tissue in plants. Almost all the primary structure like leaves, flowers and young stem made up of parenchyma.
Cells in parenchyma are living cells. They can be either round, suare or polyhedral. There are different types of parenchymatous cells.
Chlorechyma: cells in this type of parenchyma have chloroplasts and are commonly seen in leaves.
Aerenchyma: air spaces are present between cells in this type of parenchyma.
This type of parenchyma is seen in plants which float on water such plants are called hydrophytes.
Storage tissue: cells in this type of parenchyma store food materials. This type of parenchyma is seen in tubers and rhizomes.
Water storage: cells in this type of parenchyma store water – such cells are seen in desert plants.
Collenchyma : collenchymas is a simple living tissue. This tissue is present in the stems of herbs and shrubs. It gives mechanical strength and support. Cells may have chloroplasts. Cells in collenchymas are short and square or long and fibre like with pointed ends. Cell wall is made up of cellulose and pectin which gives. Collenchyma gives flexibility and tensile strength to the plants.
Sclerenchyma : sclerenchyma is a tissue with dead cells and is designed to give mechanical strength to the plant. It also protects the parenchyma from damage due to stretching, bending and pressure lignin is the major component in cell walls of the cells present in sclerenchyma.
Xylem: xylem is a conductive tissue which has both living and non-living cells. It conducts water and minerals from roots to other parts of the plant. A part from this xylem gives mechanical strength to plant. Xylem tissue is also helpful in identifying the plant species.
There are three kinds of non-living cells in xylem- they are fibers, tracheas and vessels. Xylem parenchyma is the living component in xylem. Cell walls of the xylem cells are thick because of lignin deposition. It is also commercially very useful.
Phloem: phloem is also called bast or leptome. Unlike xylem, phloem is a living tissues. Cell walls have lignin deposition. Phloem is composed of five types of cells. They are sieve cells, sieve tubes, companion cells, phloem fibres and phloem parenchyma.
Sieve cells and sieve tubes are long with tapering ends. Sieve plate with one to many sieve pores is present at the ends of sieve tubes. The conductuion of food material from leaves to other parts takes place through phloem tissues. Besides, phloem has commercial value- bast fibres present in phloem are used for making ropes.