158 THE JOUENAL OF INDIAN BOTANY.
and arched surfaces of the leaf. In sections of the basal portion, the palisade tissue disappears all along the flat surface. Gaps in the palisade tissue are filled in by palisade-like aqueous cells along the flat surface and by polygonal aqueous cells at the angles and along the middle portion of the arched surface. Some of the polygonal aqueous cells at the angles contain large clustered crystals.
The aqueous tissue consists partly of a I continuous layer of subepidermal aqueous cells many of which contain clustered crystals, and chiefly of a centrally placed mass of large aqueous cells which enclose the central veins as well as the smaller ones lying at the periphery of the aqueous tissue. The centrally placed aqueous tissue is bounded by a layer of cubical or tabular cells in those parts where the palisade tissue is present in S. foetida and H. recurvum respect- ively. Cells of this layer contain chlorophyll and resemble cells of bundle-sheaths. This layer may assist the assimilatory tissue in carbon assimilation as well as serve to bring into contact the assimilatory and vascular tissue. Some of the peripheral cells of the central aqueous tissue contain clustered crystals in the neighbourhood of the veins.
Oxalate of lime is found in the form of clustered crystals which are found in subepidermal aqueous cells as well as in aqueous cells of the central tissue in the neighbourhood of peripheral veins. Internal glands are not found in the leaf and axis of any members.
The system of veins consists of centrally placed veins, of veins traversing the central aqueous tissue and of peripheral veins situated beneath the sheath-layer which forms a bundle-sheath common to all the veins and which brings into contact the assimilatory and vascular tissues. The central vein in S. foetida is embedded in a cylinder of stone-cells, while that in H. recurvum is surrounded by a tissue of small thin-walled parenchymatous cells.
Hairy covering on the leaf and axis of S. foetida consists of uniseriate trichomes seated on larger epidermal cells. Hairs are composed of a, basal portion of a few short cells and of an irregularly curved and pointed terminal portion which consists of longer cells with walls covered with solid papillae (fig. 287). Hairs are not found in both the species of Haloxylon. External glands do not occur in any of the members.
Structure of the Axis. — Epidermal cells in H. recurvum have outer walls thickened and papillose; those in H. salicornicum are tabular and thin-walled and those in S. foetida are small polygonal cells with outer walls thickened and granulated. Stomata have the same characters as those on the leaf. Primary cortex is characterised by a sub-epidermal continuous layer of collenchyma in S. foetida, by
