in P. irregularis it is single layered on a small portion on one side, indicating the prostrate or inclined nature of the axis, sclerenchymatcus pericycle being least developed on the lower side of the axis. There are thin-walled colourless cells between and on either side of some of the groups of bast-fibres in P. irregularis; they may occasionally serve as acqueous cells.
The wood is composite with vessels uniformly distributed in the interfascicular wood-prosenchyma. In P. irregularis the vascular ring is narrowed on the side where the sclerenchymatous pericycle is reduced; there are very few vessels in this portion which is mostly occupied by interfascicular wood-prosenchyma. This may be accounted for by the fact of less vigorous functional activity on the lower side of the prostrate or inclined axis of P. irregularis. Vessels are large and few and are arranged in incomplete rows. Medullary rays are usually uniseriate and numerous.
The pith is composed of very thin-walled cells.
CARYOPHYLLACEAE.
Polycarpaea corymbosa Lam.—Figs. 42, 43, 44. Epidermal cells of the leaves with outer walls thickened and papillose. Guard-cells accompanied by subsidiary cells. The front cavity greatly depressed in the axis. Mesophyll isobilateral. Abundance of cells with tanniniferous contents characteristic of the leaf and axis. Oxalate of lime in the form of clustered crystals. Assimilatory tissue in the axis formed of chlorenchyma. Pericycle composed of large groups of stone cells with a sclerenchymatous tissue on its outer side. Wood composed of large xylem bundles separated by strands of tissue, resembling medullary rays, continuous with the outer sclerenchyma. Large water-storing tracheids with reticulate markings in the xylem bundles near the medullary-ray-like strands. Pith formed of thick-walled cells.
Structure of the Leaf:—The epidermis consists of polygonal cells with outer walls thickened and papillose (fig. 42). The cuticle is smooth. The lateral and inner walls are thin and the former are wavy.
The stomata occur on both the surfaces and the guard-cells are accompanied by subsidiary cells. The guard-cells are elevated and the front cavity is placed in a depression formed by the papillose outer epidermal walls. The stomata on the axis are greatly depressed, as the guard-cells are situated below the surrounding cells (fig. 43). In addition to the subsidiary cells, there are sometimes found one or more cells clasping the guard-cells on one or both sides of the stomata on the axis (fig. 43).
The mesophyll is isobilateral and is composed of palisade tissue.
