Page 6 - LN-ANATOMY OF FLOWERING PLANT

Different functions performed by sderenchyma are
(a) It provides mechanical strength and support.
(b) Surface fibres help in dispersal of seeds.
2. Complex Permanent Tissues
Complex permanent tissues are a group of more than one type of cells having
common origin and working together as a unit.
The main complex tissues in vascular plants are xylem and phloem.
Xylem
Xylem (Gr. Xylos — wood) is a complex permanent tissue which conducts water and
mineral nutrients upwards from the root to the leaves.
The xylem tissues are composed of four components
a. Tracheids These are elongated, tubular and primitive cells with tapering end walls.
They are dead cells and do not contain protoplasts. The inner layers of the cell walls
have thickenings which vary in form. The end of the tracheids are tapering, blunt or
chisel like. These are constituents of xylem of primitive plants.
These are found in pteridophytes and gymnosperm tracheids may be classified as
annular or helical, spiral and scalariform or pitted.
The tracheids conduct water and dissolved mineral elements from roots to leaves.
They also provide mechanical support.
b. Vessels These are long, cylindrical, tube-like structures made up of many cells
called vessel members, each with lignified walls and a large central cavity.
The vessel cells are also devoid of protoplasm. The vessel members are
interconnected through perforations in their common walls. The presence of vessels
is a characteristic feature of angiosperms.

c. Xylem Fibres The sclerenchymatous fibres associated with the xylem are called
xylem fibres. These fibres have lignified cell walls. The thickness of the walls varies
considerably, but these are usually thicker than the walls of the tracheids in the same
wood. These are found in both primary and secondary xylem. The xylem fibres
provide mechanical strength.
d. Xylem Parenchyma The parenchyma cells associated with the xylem form xylem
parenchyma. These cells form the only living component of the xylem. Xylem
parenchyma stores food in the form of starch.
These cells assist direcdy or indirecdy in the conduction of water upward through the
vessels and tracheids.