palisade and spongy tissue. Palisade is unilayered, consists of thin columnar cells,
and occupying more than half thickness of the lamina. Spongy cells are loosely
arranged with large air spaces leading to stomatal cavities (Fig.5.5c, d).
Transection of midrib (Fig.5.5a, b) shows a single collateral vascular bundle. Small
groups of collenchyma cells are present beneath the upper epidermis and inside the
lower epidermis. A few laticifer ducts with yellow-brown secretions are found in
the phloem (Evert 2006 ). Cluster crystals of calcium oxalate (Fig.5.6e, f) are
commonly found in the mesophyll, and phloem parenchyma of the veins (Hayward
1938 ).
The petiole is more or less triangular in cross section showing a groove at the
adaxial side (Fig.5.6a). The epidermis is unilayered and produces numerous
nonglandular and glandular trichomes. A ring of collenchyma is located adjacent to
the epidermis, which is narrow near the groove and much wider at the abaxial and
lateral sides. The vascular bundle is collateral with xylem above and phloem below.
The vessel elements are arranged in radial rows. A few laticifer ducts are found in
the phloem. The space surrounding the midrib vascular bundle isfilled with
chlorenchyma (Hayward 1938 ).
The stem has a wavy outline in transection due to ridges and furrows (Fig.5.5e).
The epidermis is unilayered and produces numerous nonglandular and glandular
trichomes. This is followed by a unilayered hypodermis and a few layers of
chlorenchyma, which is lined by the endodermis layer. The pericycle is wide,
consisting of numerous pericyclicfibers distributed among large polygonal par-
enchyma cells. Thesefibers have thickened and lignified walls and narrow lumina,
and measure about 5– 20 μm in diameter. The secondary phloem forms a narrow
ring, and consists of bast (phloem)fibers, parenchyma and a few laticifer ducts
filled with yellow-brown contents. Cambium is wide, made up of several layers of
radially arranged cells. The xylem comprises of large vessel elements, which are
about 30– 100 μm in diameter, circular or angular in cross section and occur soli-
tarily or a few arranged in radial rows. The xylemfibers have thickened and
lignified walls and are arranged in radial rows (Hayward 1938 ) (Fig.5.5e, f).
Transection of a primary root (Fig.5.6c, d) shows a unilayered epidermis and a
layer of hypodermis. The cortex is wide and parenchymatous. The endodermis is
unilayered and the pericycle is multilayered. The vascular bundle consists of a
diarch xylem and two groups of primary phloem (Hayward 1938 ).
In cross section, the pericarp of the fruit (Fig.5.6b) shows the following tissue
arrangement: the outermost layer, the epicarp, is made up of thick-walled scle-
renchyma cells showing sinuous anticlinal walls in surface view. The hypodermis
consists of one or more layers of loosely arranged spongy parenchyma cells.
Numerous vascular bundles traverse this region. The third zone consists of a layer
of brown cells with thick walls. This is followed by a narrow region of colorless,
collapsed cells with thin, sinuous radial walls. The innermost layer of the pericarp is
made up of palisade cells with heavily thickened walls and narrow lumina
(Hayward 1938 ; Winton 1906 ).
5 Morpho-Anatomy of Marijuana (Cannabis sativaL.) 133