184 THE JOURNAL OF INDIAN BOTANY. 



palisade tissue on the adaxial side and of arm-palisade tissue on the 

 abaxial side. Veins not provided with bundle-sheaths. Clustered 

 crystals occurring in the leaf and axis. Assimilatory tissue in the 

 axis formed of chlorenchyma. Wood composite. Pith formed of 

 thin-walled cells and forming occasionally an aqueous tissue. 



ZygOphyllum simplex L. Figs. 75, 76. Epidermal cells poly- 

 gonal. Guard-cells elevated. Mesophyll composed of a subepidermal 

 composite ring of palisade cells enclosing a massive aqueous tissue 

 surrounding the central vascular bundles. Veins embedded. Perip- 

 heral veins numerous, strengthening the aqueous tissue and provided 

 with sheaths of thick-walled cells, the outer ones containing 

 chlorophyll and the inner ones containing clustered crystals. Veins 

 traversing the aqueous tissue. T. S. of the axis kidney-shaped with 

 angles projecting outwards at the grooved surface. Primary cortex 

 forming an aqueous tissue. Wood composite. Pericycle distinctly 

 isobilateral. Pith of thin-walled cells and forming an aqueous 

 tissue. Clustered crystals numerous in the axis. 



Fagonia cretica L. Figs. 77, 78. Epidermal cells with outer 

 and inner walls convexly arched outwards and inwards. Outer walls 

 superficially granulated. Guard-cells elevated. Mesophyll isobila- 

 teral. A group of palisade like cells faintly green and perhaps with 

 a water-storing function, occurring between the lower epidermis and 

 the vein of the mid-rib. Oxalate of lime not occurring in any form. 

 Veins embedded and provided with bundle-sheaths of thin-walled 

 cells. Assimilatory tissue in the axis formed of palisade cells. Wood 

 composite. Pith formed of thin-walled cells. 



Structure of the Axis. — The epidermis consists of tabular cells 

 with outer and inner walls convexly arched outwards and inwards 

 respectively. The lateral walls are usually straight. The outer walls 

 are superficially graiulated in Tribulus alatus, Fagonia cretica and 

 Zygophyllum simplex. Large water-storing cells are intercalated 

 amongst the ordinary epidermal cells in Seetzenia orientalis (fig. 71). 

 Epidermal cells are thin- walled ; this can be accounted for by the 

 fleshy character of the leaves. 



The stomata occur on both the surfaces, though more numerous 

 on the lower ; they are surrounded by 3-6 ordinary epidermal cells. 

 Guard-cells are elevated in species of Tribalus, Fagonia cretica 

 Zygophyllum simplex (fig. 75), so that the front-cavity is on a level 

 with the surface. In Seetzenia orientalis (fig. 72), the stomata are 

 depressed and the guard-cells are either in the same plane or in a 

 plane lower than that of the surrounding cells. 



The elevated position of the stomata in species of Tribulus may 

 be due to a protective covering of hairs and to the subepidamal 



