Page:The Journal of Indian Botany.djvu/326

 level with the surface. The sfcomaba on the axis are found at the apex of pedestals formed by epidermal cells. The pedestals are quite conspicuous in Melothria viaderaspatana (tig. 138).

The mesophyll is composed of palisade cells, which are much shorter in Momordica dioica and Cucumis Melo, on the adaxial side and of an extensive spongy tissue on the abaxial side. The spongy tissue is replaced by arm-palisade tissue in Citrullus Colocynthis. There are groups of colourless palisade-like cells below the lower epidermis of Citrullus Colocynthis ; these groups of cells may form water-cells.

The veins are embedded and are not provided with bundle-sheaths. They are vertically transcurrent.

The hairy covering consists of clothing and glandular hairs. The clothing hairs are more numerous on the lower surface and consists of simple uniseriate thin-walled trichomes seated on subsidiary cells which are raised above the base of the trichomes in Cucumis Melo (fig. 134) and in Melothria maderaspatana. The trichomes on the axis are accompanied by numerous subsidiary cells, which form a pelestal-like structure (fig. 132). The constituent cells of the trichomes are dilated at the base, thus giving them a somewhat jointed appearance.

The external glands on the leaf and axis are composed of a short uniseriate stalk usually placed in epidermal depressions and of an ovoid head divided by horizontal and vertical walls. Glandular hairs seem to be more numerous on the upper surface in Momordica dioica.

Structure of the Axis. — The epidermis consists of small polygonal cells with outer walls a little thickened. Axes are deeply five-grooved except in Citrullus Colocynthis where the ridges and the furrows are very slight.

The cortex is characterised by an assimilatory tissue formed of chlorenchyma. The collenchyma is sub-epidermal ; it is developed in the angles in Momordica dioica and in Melothria maderaspatana (fig. 136) ; in Cucumis Melo it forms a continuous ring thickened in the angular portions. In Citrullus Colocynthis collenchyma is developed below the epidermis of the larger angles.

The pericycle forms a composite undulated ring of stone-cells except in Citrullus Colocynthis where it is composed of closely placed groups of stone-cells.

The vascular bundles are bicollateral and are arranged in two rings five in each ring. The bundles in the outer ring are much smaller and occur below the angles where they are conspicuous. Smaller bundles project towards, the exterior and the larger towards