Tissue

• A group of cells having similar origin, structure and function is called tissue. Tissues are really formed in response to a basic division of labour. The term tissue was coined by N. Grew (1682).
• Based on the capacity to divide, the plant tissues have been classified into two fundamental types, meristematic and permanent.
• A simple tissue consists of only one type of cells e.g., meristem, parenchyma, etc. while a complex tissue has two or more types of cells e.g., xylem and phloem.

MERISTEMATIC TISSUE

Meristematic tissue, commonly called meristem (Gk. meristos: divisible) is composed of cells which possess the power of cell division. The term 'meristem' was introduced by C. Nageli (1858) for a group of continuously dividing cells.

characteristics of meristems

• Cells of meristems are living and are at active divisional stage.
• The cells are usually small and isodiametric. The cells of cambium are, however, elongated.
• The cells are compactly arranged without any intercellular spaces.
• The cell wall is thin and made up of cellulose.
• Cytoplasm is dense, granular with a central, large and prominent nucleus.
• Vacuoles are either very small or absent. The cells of cambium are, however, vacuolated.
• Metabolic activity is high, so is the rate of respiration.
• Cytoplasm has all the cell organelles, but instead of plastids there are proplastids  (elaioplasts)
• Ribosomes are abundant, ER is simple.

classification of meristems

• Meristems have been classified on the basis of origin, position, function and plane of cell division.