Stomata occur on both the surfaces, being a little more numerous on the lower. Guard-cells are elevated above the plane of the surrounding cells and the front cavity is a little raised above the surface. Stomata are surrounded by 3-4 ordinary epidermal cells.
The mesophyll is composed of short palisade cells on either side without a middle tissue except for a layer of polygonal cells containing clustered crystals in the middle of the mesophyll in B. odorata.
Internal secretory cells are not found in the leaf. Oxalate of lime occurs in the form of numerous clustered crystals near the veins. In B. odorata there is a layer of polygonal cells with clustered crystals in the middle of the mesophyll (fig. 51). In the axis clustered crystals occur in the cortical parenchyma and pith. Veins are provided with sheaths of green thick-walled cells. Larger veins are vertically transcurrent above and below by colourless parenchyma.
Hairy covering on the leaf and axis consists of clothing and glandular hairs. Clothing hairs are partly unicellular and partly uniseriate trichomes. They are not found on the leaf of B. ammanioides and those on the axis are very thin-walled. Glandular hairs occur only in B. odorata and are of a shaggy type; they are composed of a multicellular stalk and of a multicellular head (figs. 51, 52).
Structure of the Axis:—The epidermis is two-layered. Outer epidermal cells have outer walls greatly thickened, the lateral walls being thin. The stomata are like those on the leaf and are surrounded by 4-5 ordinary epidermal cells. The primary cortex is characterised in its outer portion by an assimilatory tissue, which in B. odorata (fig. 52) is composed of short palisade cells and in B. ammanioides (fig. 66) of chlorenchyma. Inner portion of the cortex is formed of large-celled cortical parenchyma.
The wood in both the species presents a quadrangular appearance. It is broader at the angles and is much narrowed between. Interfascicular wood prosenchyma is extensive. The medullary rays occur in B. odorata and are 1-2 seriate. The vessels are arranged in rows. Wood parenchyma is scantly developed.
The pith is composed of thin-walled cells. Internal secretory organs are represented by secretory cells with tanniniferous contents. They occur in the cortical parenchyma in the soft bast and pith of B. odorata and only in the pith of B. ammanioides.
MALVACEAE
Sida grewioides Guill.—Figs. 53, 54. Woody. Stomata more numerous on the lower surface. Internal glands numerous in the mesophyll. Clustered crystals occurring near the veins of the leaf and in the soft bast of the axis. Clothing hairs tufted and more
