The genus Cinnamomum

Botany and Crop Improvement of Cinnamon and Cassia 27
hypertrophied dictyosomes budding off the vesicles. Mucilage has just started to be
deposited as a layer between the suberised layer and the cytoplasm. The cell membrane
is pushed inside hard the inner vacuole is still intact. In stage 3b, the cytoplasm consists
mainly of dictyosome vesicles full of mucilage and they finally fuse with plasmalemma.
The cytoplasm has been forced to move inward by the accumulated mucilage and the
central vacuole gets reduced considerably. In stage 3c, the cell is mostly round, the
suberised layer is 37 7 nm thick, and the cell is completely filled with mucilage.
Cytoplasm gets degenerated and the vacuole disappears completely. Main similarities
and differences between the developmental stages of oil and mucilage idioblasts are
given in Table 2.3.
Foliar epidermal characters
Ravindran et al. (1993) and Baruah and Nath (1997) studied the foliar epidermal characteristics
in several species of Cinnamomum, including C. verum, C. cassia, C. camphora
and C. tamala.
Epidermis
Epidermis consists of a single layer of cells covered by smooth cuticle. Cuticle is thick on
the upper surface, thin on the lower. Epidermal cells are of two types: (i) In C. camphora
(and also in species such as C. parthenoxylon, C. cecidodaphne and C. glanduliferum) cell
walls are straight or only slightly curved; (ii) In C. verum, C. cassia, C. malabatrum,
C. tamala, etc. cell walls are sinuous (Fig. 2.4). Epidermal walls of different species
show varying degrees of birefringence and autofluorescence of cell walls, which indicate
sclerification (Bakker et al., 1992).
The epidermis in many species possesses trichomes. Often (as in C. verum, C. cassia)
trichomes are microscopic and occur only on the lower surface, but in species like
C. perrottettii both leaf surfaces are hirsute and trichomes are visible to the unaided eye.
Trichome distribution is sparse in C. verum, in certain C. malabatrum collections, moderately
dense in C. cassia and dense in C. perrottettii (Ravindran et al., 1993). Trichomes
are short (less than 0.1 mm), medium (0.1–0.2 mm) or long (above 0.2 mm).
Structurally trichomes are identical. They are unicellular, unbranched and nonglandular,
thick walled, and enclose a narrow lumen in the centre. In C. bejolghota the trichomes
are papillate (Baruah and Nath, 1997).
Christophel et al. (1996) used leaf cuticular features in relation to taxonomic delimitation
in Lauraceae. They found that South American species of Cinnamomum have
distinctive cuticular signatures and that they are clearly different from the species
occurring in Australia. Interestingly the American species of Cinnamomum studied by
the above authors had been earlier placed in the genus Phoebe. Asian species of the
genus, including the type species, form a third distinctive group. Further study may
well lead to the conclusion that the group is not natural (and is perhaps polyphyletic)
as it is currently defined (Christophel et al., 1996).
Venation pattern
Kim and Kim (1984) studied the venation pattern in some Lauraceae using soft X-ray
analysis and reported acrodromous venation in C. camphora, C. japonicum and C. loureirii.