The pith consists of thin- walled cells.
MORINGASEAE
Moringa pterygosperma Gaert.-* Figs. 96, 97. Leaf. Water- storing cells vertically elongated, conspicuous and numerous in upper epidermis. Mesophyll formed of palisade tissue on the adaxial side and of spongy tissue on the abaxial side. Myrosin cells in the form of palisade-like cells and confined to the palisade tissue. Oxalate of lime absent. Veins enclosed in bundle-sheaths. Short unicellular clothing hairs occurring on both surfaces.
Moringa concanensis Nimmo: — Eig, 98. Leaf. Water-storing cells in upper epidermis few and formed of a little enlarged epider- mal cells. Lower epidermal cells with outer walls forming large papillae. Mesophyll composed of rows of palisade cells separated by myrosin cells on the adaxial side, and of armpalisade tissue on the abaxial side. Myrosin cells occurring between the rows of palisade cells as well as on the inner side of arm-palisade tissue. Clustered crystals of oxalate of lime numerous near veins and below lower epidermis. Veins not enclosed in bundle-sheaths but strengthened by arcs of stone-cells on their lower side. Hairs absent.
Structure of the Leaf : — The epidermis differs in structure on the two surfaces. The epidermal cells on the upper surface are tabular with outer and inner walls equally thickened and convexly arched outwards and inwards respectively. There are large water-storing cells, which are numerous and conspicuous in M. pterygosperma (fig. 96) intercalated amongst the ordinary epidermal cells, (figs. 96, 98). The epidermal cells on the lower surface are much smaller than those on the upper surface. The outer and inner walls are equally thickened and the latter are curved convexly outwards in the form of papillae which are very large in M. concanensis (fig. 96). Lateral walls are thin and straight.
Stomata occur only on the lower surface and are surrounded by ordinary epidermal cells. Guard-cells are situated quite below the plane of the epidermal cells. The front cavity is therefore placed in a pit as deep as the height of the epidermal cells ; air in these pits remains moist and transpiration is thus greatly diminished. This kind of contrivance is necessary in leaflets of species of Moringa which are not protected by a dense covering of hairs and which, on the other hand, are greatly shaken by wind, thus accelerating transpiration.
The hairy covering consists of a few short, thick-walled unicellu- lar clothing hairs found on both the surfaces of M. pterygosperma (fig. 96) ; it does not occur in M. concanensis. External glands are absent.
