(Structural Organisation) Learning Objectives The Tissues A Tissue is a group of cells that are alike in origin, structure and function. The study of tissues is called Histology. A plant is made up of different types of tissues. There are two principal groups: .
Meristematic tissues . Permanent tissues . Meristematic Tissue . .
Characteristics and classification The characters of meristematic tissues: (Gr . Meristos- Divisible ) Apical meristem Intercalary meristem Lateral meristem Figure . : Different types of meristems on the basis of position in plant body The term meristem was coined by C. Nageli .
• The meristematic cells are isodiametric and they may be, oval, spherical or polygonal in shape. • They generally have dense cytoplasm with prominent nucleus. • Generally the vacuoles are either small or absent. • Their cell wall is thin, elastic and made up of cellulose.
• These are most actively dividing cells. • Meristematic cells are self-perpetuating. Classification of Meristem Meristem has been classified into several types on the basis of position, origin, function and division. Theories of Meristem Organization and Function Many anatomists illustrated the root and shoot apical meristems on the basis of number and arrangement and accordingly proposed the following theories – An extract of which is discussed below.
Shoot Apical Meristem Apical Cell Theory Apical cell theory is proposed by Hofmeister ( ) and supported by Nageli ( ). A single apical cell is the structural and functional unit. Classification of Meristem Position Origin Function Plane of division Lateral meristem Occurs along the longitudinal axis of stem and root. It is responsible for secondary tissues and thickening of stem and root.
Example: vascular cambium and cork cambium. Apical meristem Present in apices of root and shoot. It is responsible for increase in the length of the plant, it is called as primary growth. Intercalary meristem Occurs between the permenant tissues.
It is responsible for elongation of internodes. Primary Meristem It is derived from embryonic initials and differentiated into primary permanent tissues. Secondary meristem It is derived during later stage of development of the plant body.