with acicular raphides (fig. 160) in the assimilatory tissue in the leaf and axis. Besides these, there are assimilatory cells in the mesophyll with tanniniferous contents (fig. 160 G.).
Oxalate of lime occurs only in S. hispida either in the form of acicular raphides in the mesophyll and pith (fig. 161 A. E.), or in the form of crystal sand in the cortex. The vains are embedded and are not provided with bundle-sheaths. "Veins of the mid-rib are vertically transcurrent above and below by collenchyma in 0. aspera.
The hairy covering on the leaf and axis in S. hispida (figs. 160, 161) consists of articulate uniseriate trichomes with the terminal cell ending in a sharp point ; trichomes on the axis are situated in groups on the wiug-like ribs at the angles (fig. 161). Trichomes are more numerous on the lower surface of the leaf. Clothing hairs are absent on the leaf of 0. aspera ; on the axis, however, there are peculiar dome-like unicellular hair-like structures with walls thickened and muriculate. Glandular hairs are not found on the leaf and axis.
Structure of the Axis. — The epidermis consists of tabular cells with outer walls greatly thickened. The outer walls are muriculate and the inner walls also thickened in 0. aspera (fig. 162). The lateral walls are thin and straight. There are large wing-like ribs at the angles of the axis in S. hispida. The cortex of S. hispida is composed of parenchymatous assimilatory tissue extending into ribs which are strengthened by collenchyma. Assimilatory cells contain rounded bodies of the nature of fat bodies. Endodermis is differentiated. Sclerenchymatous pericycle is found only in S. hispida and is com- posed of a loose ring of bast fibres.
The vessels are arranged in complete rows and are larger in the lower half of the wood. Interfascicular wood prosenchyma is scantily developed and is formed of cells with thin walls and with large lumina. Medullary rays are uniseriate and numerous. The abundance of vessels and the scanty development of interfasicular wood prosencby ma are characteristic of the herbaceous nature of the plants.
The pith is composed of thin-walled cells.
(To be continued.)
