Numerous large clustered crystals of oxalate of lirne occur in the arm-palisade tissue of the mesophyll. The crystals are wanting in the axis. The veins are embeded and are not provided with bundle-sheaths.
Both the leaf and the axis are devoid of hairs. The absence of hairs is compensated for by the gelatinisation of the inner walls of the epidermal cells.
Structure of the Axis:—Epidermis consists mostly of tabular cells with outer walls thickened, muriculate and convexly arched outwards. The inner walls are gelatinised and the lateral walls are straight. The epidermis is distinguished by two common features (l) palisade-like elongation of the epidermal cells in some parts (2) gelatinisation of the inner walls of the epidermal cells which are sometimes characterised by thin dividing walls parallel to the surface beneath which mucilage is found. The epidermis may occasionally serve as a water-storing tissue on account of these two features.
Cells of the outermost layer of the cortex show collenchymatous differentiation at their outer angles. The cortex is distinguished by the occurrence of cortical vascular bundles in the cortical chlorophyll containing parenchyma.
Sclerenchymatous pericycle is absent. The structure of the wood is composite. The vessels are small and are arranged almost in numerous complete rows. Interfascicular wood-prosenchyma is little developed. Medullary rays are uniserate and numerous. Small-celled collenchyma occurs at the inner margin of the wood. Soft bast forms a continuous ring.
The pith consist of thin-walled cells.
POLYGALACEAE.
Polygala erioptera DC.—Figs. 38, 39. Leaf and axis.— Numerous lysigenous cavities in the lower half of the mesophyll. Clustered crystals occurring near the veins. Compact bundles, comb-like at their ends, of diamond shaped bodies in the palisade-like cells in the upper half of the mesophyll. Epidermis of the axis two- layered. Axis ribbed. Eibs strengthened by stone- cell groups. Assimilatory tissue of the axis formed of palisade tissue. Sclerenchymatous pericycle in the form of groups of thick-walled and stratified bast fibres with small lumen.
Polygala irregularis Boiss.— Figs. 40, 41. Axis only.—Axis ribbed, groups of stone-cells strengthening the ribs. Epidermis one-layered. Assimilatory tissue composed of chlorenchyma. Aqueous cells between the groups of bast fibres. Sclerenchymatous
