Page:The Journal of Indian Botany.djvu/282

 Stomata are depressed and are found equally numerous on both the surfaces of the leaf when it is isobilateral, or are more numerous on the lower surface when it is bifacial. Stomata are surrounded by ordinary epidermal cells.

The mesophyll is isobilateral in G. Bitrhia fig. 100, species of Indigofera figs. 104, 106 and P. odorata fig. 108. It is bifacial in H. latebrosa, G. medicaginea, A. vaginalis, P. trilobus and species of Rhyncosia. The chief character of the mesophyll is the occurrence of large cells, distinguished by shape and contents in the middle of the mesophyll ; they hold tanniniferous contents and are especially prominent in species of Indigofera figs. 104, 106, Tephrosia and Rhyncosia. In species of Crotalaria, Psoralea and Alysicarpns there is a layer of large polygonal cells in the middle, poor in chlorophyll and perhaps occasionally serving as an aqueous tissue. P. trilobus does not possess any differentiated layer of cells in the middle of the mesophyll.

The isobilateral arrangement of the palisade tissue is common and spongy parenchyma, when present on the abaxial side, is scantily provided with intercellular spaces. The reduction of the ventilating system in the mesophyll is a proof of the xerophytic nature of the plant.

Internal secretory organs are represented by tannin sacs. They occur in the middle of the mesophyll in I. cordifolia and in species of Tephrosia and Rhyncosia and in the palisade tissue in I. paucifolia and P. trilobus. In species of Crotalaria and Psoralea tannin sacs are very few and occur in the neighbourhood of the veins. Tannin sacs are not found in species of Heylandia and Alysicarpns. Sec- tions of the leaf of C. medicaginea were found to be mucilaginous while changing them from lactic acid to glycerine ; this may suggest the presence of mucilaginous cells in the mesophyll.

P. odorata is characterised by the occurrence of intercellular secretory receptacles, termed intramural glands. They occur close beneath the epidermis in the palisade tissue and are bounded towards the palisade tissue by a sheath of cells closely fitting together. The space is traversed by a number of narrow tubular secretory cells, curved more or less like meridians. The external walls of these cells are thickened and take part in the formation of the surface of the leaf. Intramural glands are much more numerous on the lower surface than on the upper.

Oxalate of lime is not found in any form in any of the members.

The veins are embedded in species of Crotalaria and Indigofera ; they are vertically transcurrent above and below by means of collenchyma in P. trilobus, by selerenchyma in species of Heylandia,