Agriculture Reference
In-Depth Information
Primary meristem
procambium
Primary xylem
Primary
phloem
Secondary
meristem
cambium
Primary phloem associated
with primary fibres
(sclerenchyma)
Secondary xylem
cambium
Secondary phloem
(associated with secondary fibres)
Fig. 3.2.
Origins and organization of the vascular tissues in hemp stems.
(secondary extra-xylem fibres are modest in
length), a thick cellular wall and a specific
chemical composition. The physical, mor-
phological and chemical characteristics of the
primary fibres make them highly sought after
by industry. The secondary fibres adjacent to
the cambium are generally left behind
during the process of fibre stripping. In both
cases, the non-xylem fibres are closely associ-
ated together in bundles orientated parallel to
the stem (Fig. 3.3). Once removed, these
bundles are commonly called 'technical
fibres'. This term contrasts with the unitary
fibre that is defined anatomically according
to strict morphological criteria (narrow
elongated cells with few punctuations). It is a
generic term that is used to describe xylem
fibres and extra-xylem cells (sclerenchyma).
The cell walls: the major constituent of
hemp fibres
The xylem and sclerenchyma tissues are dead
and devoid of protoplasm. As cell growth
comes to an end, the walls of these cells
become thickened by the laying down of the
parietal polymers, cellulose, hemicellulose and
lignin. This thickening corresponds with the
development of rigid secondary walls attached
to the existing parietal strata. At maturity, the
