Discussion
The leaf outline was āVā shaped in all Habenaria species. In all
species studied, the cuticle was smooth on leaf surface. The cuticle
thickness was greatest in all studied species. The cuticle is a thick,
hydrophobic membrane composed of a polymer matrix (cutin) and associated
with solvent soluble lipids (cuticular waxes) ( Rasmussen, 1987); Angelaet. al 2015). Plant cuticle plays an important role in the
interaction of plant with environment, helps to reduce water
transpiration ( Fahn 1982; Rindyastuiti et .al 2018).Habenaria species has a variation in cuticle thickness, the thick
cuticle is an ecological adaption to reduce transpiration (Moreiraet. al 2013).
Epidermis is the outer cell layer of a leaf, act as a barrier between
the leaves and environment it is also important in maintaining the
external stimulus (Dietz and Hartung 1996). Epidermis is important to
protect mesophyll and vascular bundles from higher solar radiation.
Thick epidermis cell helps to reduce water transpiration.
Large epidermal cell in many species of orchids serve as water storage
(Guan et .al 2011). Size of the epidermal cell is significantly
different among species. Larger epidermal cells support the species to
be more adaptive to the warmer environment . epidermal cell has various
shape among species such as polygonal, isodiametric rectangular and
elongated. (Aybake et.al .2010).
The hypodermis is a structure beneath the epidermis this structure can
be present or absent in orchid species (Pridgeon 1982; stern 1997;
Rindyastuti et.al 2018). Along with epidermis, hypodermis protect
the mesophyll cells & vascular bundles. In the present study hypodermis
was absent or not clear in the Habenaria species.
The mesophyll is important structure for leaves that is filled with
photosynthesis component (chlorophyll) to assimilate nutrients. The
number of mesophyll layers in the present study varies. The thicker
leaves supports the leaves succulence. The succulence level of leaves
related to the parenchymal capacity of mesophylls, to provide water
supply for photosynthetic process and leaves cells, turgor mainly in the
dry environment (Hsiao 1973; Lack and Evans 2001; Metusala et.al2017). In the present study Habenaria elwessi Hook.f has more
mesophyll layers than the other Habenaria species. In present
study Habenaria species shows mesophyll layer is made with
homogenous parenchymatic cells.
The vascular bundle is a transport system containing xylem and phloem
that are important in the water and nutrient transport (Lack and Evans
2001; Fahn 1982).
The vascular bundles arrangement in the mesophyll of Habenariaspecies has aligned in rows in the center of mesophyll. Vascular bundles
arrangement in a single row was reported in Habenaria cornuta ,H . holothrix, H . monorrhiza, H. occidentalis, H.
odontoptala, H. snowtenii, H. vaginatum. (Stern 1997) in present study
sclerenchyma cells were not associated with xylem and phloem. Bundle
sheath consisted of cells surrounding the vascular bundle. Bundle sheath
cells were made with thin walled parenchymatic cells. Fibre bundles,
spiral thickening, raphide bundles were absent or not clearly visible.