Page:The Journal of Indian Botany.djvu/786

278 THE JOURNAL OF INDIAN BOTANY. The sfcomata are depressed and are either present only on the upper surface or are more numerous on the upper surface. The guard-cells are elevated arid are accompanied by subsidiary cells one on either side. The veins are numerous and are enclosed in complete or incomplete sheaths. The larger veins are vertically transcurrent above and below by stereome bundles. The assimilatory tissue in the leaf consists of complete girders of palisade cells round the smaller veins and of arcs of palisade cells on sides of the vertically trans- current veins. The spongy tissue is altogether absent. The veins with the accompanying assimilatory tissue are sometimes separated from one another by vertical strands of articulation tissue.

The mechanical tissue in the leaf-blade occurs in the form of I-girders the webs of which are formed by mixed or unmixed vascular bundles of the veins. The margins especially when thay are bluntly pointed are strengthened by large stereome bundles. The epidermis of the axis consists of small cells with the outer walls greatly thick- ened and silicified. The assimilatory tissue consists of palisade tissue or of chlorenchyma ; it is absent in some members. The mechanical tissue is represented by a stereome tube supplemented by isolated sub-epidermal girders.

Vascular bundles are of two sizes, the smaller ones being usually embedded in stereome strands formed by the sub-epidermal girders and by flanges of the stereome tube. Of the larger vascular bundles the peripheral ones are usually apposed to the inner side of the stereome tube and the rest are scattered in the medullary tissue. The medullary tissue usually consists of thin-walled cells, which, in some members, are filled with starch grains.

Actiniopteris dichotoma Bedd. — Figs. 360, 361. A segment of the frond : — Upper epidermis of sclerotic cells and accompanied by sub-epidermal stone tissue. Lower epidermis of small tabular cells with outer walls thickened and toothed, and with groups of stone- cells intercalated amongst them below the stele- Stomata on the lower surface and accompanied by ordinary epidermal cells. Assimila- tory tissue consisting of chlorenchyma. Stele supported above and below by epidermal stone-tissue. Hairs absent.

Stipe : — Epidermal cells sclerosed except at the angular por- tion, and accompanied by sub-epidermal stone-tissue. Cuticle tooth- ed. Stomata in angular portion. Assimilatory tissue consisting of chlorenchyma. Hairs long and unicellular. Stele in the centre.