18fi THE JOURNAL OF INDIAN BOTANY. 



storing function, intercalated amongst the ordinary epidermal cells 

 (fig*. 73), Epidermal cells in F. cretica are tabular with outer walls 

 thicksned and cuticularised and with lateral walls thin and straight, 

 Epidermis in Z. simplex is composed of polygonal cells with outer 

 walls thickened and papillose. Outer walls are superfic ially granula- 

 ted in all members except T. terrestris. The stomata are like those 

 on the leaf. 



The primary cortex in species of Tribulus is characterised by the 

 presence of a layer of subepidermal collenchyma below which occurs 

 cortical parenchyma with a water-storing function. The cortex in S. 

 anentalis consists of chlorenchyma and forms an assimilafcory tissue ; 

 it forms an aqueous tissue strengthened in the projecting angular 

 portions by small stone-cell groups in Z. simplex. In F. cretica it 

 consists on its outer side of an assimilatory tissue of palisade cells 

 and of an inner portion of an aqueous tissue ; it is strengthened by 

 stone-cell groups which can be roughly arranged in three rings, the 

 outermost groups being the largest and almost subepidermal in 

 position and giving a ribbed appearance to the axis. 



The pericycle is composed of rhomboidal groups of stone-cells in 

 species of Tribulus, S. orientalis and F. cretica. The stone-cell 

 tissue is extensive and is necessary to strengthen the massive cortical 

 aqueous tissue. The pericycle in Z. simple c is composed of stone-cell 

 groups and presents an isobilateral arrangement ; the stone-cell tissue 

 along the grooved portion is greatly reduced and consists of isolated 

 stone-cells or of very small groups. 



In prostrate axis of species of Tribulus and of S. orientalis the 

 stone-cell tissue is more extensive along the upper portion of the axis. 

 In spite of the prostrate habit of the axis of F. cretica the pericycle 

 does not seem to be much affected except that the stone-cell groups 

 are closer together on the upper side. 



The structure of the wood presents an isobilateral appearance in 

 all the members. Wood forms a composite hollow cylinder formed of 

 closely placed xylem bundles. Interfascicular wood prosenchyma is 

 little developed. Wood prosenchyma encloses the lower portion of 

 the xylem bundles in T. terrestris, while in T. alatus it is replaced 

 by wood parenchyma ; this may form a specific difference. Me- 

 dullary rags are absent except in F. cretica where uniseriate rays 

 occur. 



Along the upper surface which is more exposed to the sun and 

 climatic factors and *vhich consequently presents greater functional 

 activity, the xylem bundles are larger with vessels larger and more 

 numerous; on the lower side which is protected from the sun the xylem 

 bundles are much smaller and the vessels smaller and less numerous. 



