and consists of stellate hairs. There are unicellular papillae-like— structures in L. indicum, (fig. 157), with walls superficially rugose and perhaps with a water-storing function.
The pericycle is composed of stone-cells, except in species of Trianthema. Wood is composite and can be classified into three types as described already. The structure of the wood undergoes modifi- cations either due to the prostrate habit of the axis or to the action of wind in case of erect axes. The perforations of the vessels are simple. The pith consists of thin-walled or thick-walled cells.
RUBIACEAE
Oldenlandia aspera DC— Fig. 162. Epidermal cells with outer walls convexly arched outwards. Mesophyll formed of short-celled palisade tissue. Unicellular dome-like structures with thickened and muriculate walls found on the axis. Epidermal cells of the axis with both outer and inner walls thickened. Internal secretory organs and oxalate of lime not found. Sclerenchymatous pericycle absent. Soft bast of thick walled-cells. T. S. of the axis circular.
Spermacoce hispida L. — Figs. 160, 161. Upper epidermal cells larger and with outer walls usually toothed in the middle. Mesophyll composed of palisade tissue on the upper side and of spongy tissue on the lower. Internal secretory cells with tanniniferous con- tents numerous in the mesophyll. Secretory cavities found in the mesophyll and cortex. Acicular crystals found in the cortex. Cloth- ing hairs in the form of articulated uniseriate trichomes. Epidermal cells of the axis with outer walls thickened. Axes quadrangular. Angles bearing wing-like ribs. Pericycle forming a loose ring of bast fibres.
Structure of the Leaf. — The epidermal cells are polygonal with the outer walls greatly thickened and convexly arched outwards. The outer walls of the upper epidermal cells of S. hispida are toothed in the middle, while those of the epidermal cells on both the surfaces in 0. aspera are sometimes papillose. Lateral walls are thin and undulated ; inner walls are thin.
The stomata are accompanied by subsidiary cells and are more numerous on the lower surface. The guard-cells are situated in the plane of the subsidiary cells which are elevated above the surrounding cells. The front cavity is placed in depressions formed by the outer thickened walls of the surrounding cells. The stomata on the axis have the same characters as of those on the leaf (Gg. 162).
The mesophyll in 0. aspera is composed wholly of short palisade cells ; it is bifacial in S. hispida. Internal glands occur -only in S, hispida, and are represented by mucilaginous secretory ^cavities
