BOTANY Higher Secondary Second Year - Textbooks Online

Fibres
Fibre cells are dead cells. They are very long and narrow with pointed
ends. In transverse section, the fibres are polygonal with narrow lumen.
The secondary wall is evenly thickened with lignin. It possesses simple
pits. Fibres are supporting tissues. They provide mechanical strength
to the plants and protect them from the strong winds. The fibres that are
found in the seed coat of some seeds are called surface fibres. eg. cotton.
Complex tissue
A tissue that consists of several kinds of cells but all of them function
together as a single unit is called complex tissue. It is of two types –
xylem and phloem.
Xylem
Brachy sclereids
Lignified wall
Lumen
Branched pits
Simple pit
Macro sclereids Osteo sclereid
A fibre
Fig. 2.4. Types of sclerenchyma
Xylem (Greek word ‘xylos’= wood) is a complex tissue that is mainly
responsible for the conduction of water and mineral salts from roots to
other parts of the plant. The xylem, which is derived from procambium,
is called primary xylem and the xylem, which is derived from vascular
cambium, is called secondary xylem. Earlier formed xylem elements
are called protoxylem, whereas the later formed xylem elements are called
73
Lignified
cell wall
Lumen