In general plant cell walls are subdivided as primary
(PW) and secondary (SW) walls. The distribution of cellulose,
hemicellulose and lignin varies considerably among these layers.
The secondary wall is composed of SW1, SW2 and SW3 where SW2
is usually thicker than the others and contains the major portion of
cellulose. The middle lamella, which binds the adjacent cells, is
almost entirely composed of lignin