PLANTS OF THE INDIAN DESERT. 221 



The vascular system consists of numerous peripheral bundles 

 seated on sub-epidermal stereome girders in all members except S. 

 quinquefarius and of a few inner bundles embeded in the ground 

 tissue. Peripheral bundles are of two sizes, larger ones alternating 

 with the smaller. Smaller bundles in species of Cyperus in F. tenera 

 and in S. maritimns are enclosed in an outer ring of stone-cells and 

 in an inner ring of green sheath-cells ; larger bundles are enclosed in 

 a single ring of stone-cells which is many layered on the inner side. 

 In G. arenarius, besides the peripheral bundles seated on the girders 

 there are other small bundles not protected by any sub-epidermal girders 

 and alternating with the former. Smaller bundles in S. quinquefarius 

 (fig. 310) occur in the assimilatory tissue and are not apposed to the 

 sub-epidermal girders ; the larger ones are placed in ground tissue 

 strands. 



The ground tissue consists of thin- walled parenchymatous cells 

 and is traversed in its outer portion by vascular bundles ; it is not 

 differentiated in the centre into pith except in C. rotundus in which 

 the central tissue is composed of a few larger thin-walled cells. The 

 ground tissue in S. quinquefarius is represented by one-layered plates 

 of parenchymatous cells enclosing large air-spaces. Vascular bundles 

 occur in the traversing plates. The occurrence of sclerenchyma in 

 the ground tissue of S. quinquefarius is the result of its being found 

 on wet ground. 



General Review. — Epidermal cells have outer walls greatly thick- 

 ened and silicified. Inner walls are angular and lateral walls are 

 straight. The upper epidermis is modified to form the aritculation 

 tissue in species of Cyperus and in F. tenera. Stomata occur only 

 on the lower surface in species of Cyperus and in F. tenera where the 

 upper epidermis forms the articulation tissue ; they are found on 

 both the surface in S. maritamus in which the epidermis on either 

 side is not modified into the articulation tissue. The guard-cells are 

 elevated and are accompanied by subsidiary cells. The front cavity 

 is either placed in a depression formed by the outer thickened epider- 

 mal walls or it is elevated above the surface. Stomata on the leaf as 

 well as those on the axis are characterised by obconical cavities 

 around which are also developed obconical groups of elongated obli- 

 quely placed cells. The photosynthetic tissue in the leaf and axis 

 consists of tabular palisade cells. Veins are numerous and are 

 arranged in a single row or in two rows larger veins alternating with 

 the smaller. Smaller veins and vascular bundles in the axis in 

 species of Cyperus and in F. tenera are enclosed in an outer ring of 

 stereome and in an inner ring of sheath-cells ; larger veins are enclosed 



