PLANTS OF THE INDIAN DESEBT. 99 



The structure of the wood differs in the two species. In T. 

 orientalis (fig. 46) the wood forms a composite solid central cylinder 

 and is composed of numerous small 'vessels embedded in interfasci- 

 cular wood prosenchyma. In T. dioica (fig. 45) the wood forms a 

 composite hollow central cylinder enclosing a small pith tissue and 

 consists of xylem bundles connected together by interfascicular wood 

 prosenchyma. Medullary rays are 2-6 seriate in T. dioica. In T. 

 orientalis they are uniseriate and few. The soft bast forms a con- 

 tinuous ring in T. orientalis, while in T. dioica it occurs in groups 

 opposite the xylem bundles. 



The pith of T. dioica is formed of thick-walled cells, those near 

 the periphery being filled with granules ; it does not occur in T. 

 orientalis. 



Internal secretory organs in both the species are represented by 

 some of the cortical cells near the periphery with tanniniferous 

 contents. 



ELATINEAE. 



Bergia ammanioides Boxb.— PI. VI, figs. 47, 48, 49. A small 

 number of cells with clustered crystals occurring near the veins. Secre- 

 tory cells with tanniniferous contents found in the pith. Clothing 

 hairs not found on the leaf. Hairs on the axis in the form of very 

 thin-walled uniseriate trichomes. Glandular hairs absent on the leaf 

 and axis. T. S. of the axis quadrangular. Assimilatory tissue in the 

 axis formed of chloroqhyll containing parenchyma. Sclerenchymatous 

 pericycle in the form of small stone-cells at the angles. Medullary 

 rays absent. 



Bergia odorata Edgeto.— PI. VI, fig. 50 ; PI. VIII, figs. 51, 52, 

 A layer of polygonal cells with clustered crystalsin the middle of the 

 mesophyll. Numerous clustered crystals near the veins. Secretory 

 cells with tanniniferous contents in the cortical parenchyma, soft bast 

 and pith. Ordinary unicellular hairs and uniseriate trichomes found 

 on the leaf and axis. Glandular shaggy hairs occurring on the leaf and 

 axis. T. S. of the axis circular. Assimilatory tissue in the axis 

 composed of short palisade cells. Sclerenchymatous pericycle forming 

 a loose ring of small groups of stone-cells. Medullary rays ]-2 seriate. 



Structure of the Leaf: — The epidermis is composed mostly of 

 horizontally tabular cells with very large water-storing cells inter- 

 calated amongst them. The water-storing cells are sometimes divided 

 by cross walls into unequal halves, the lower half being much larger 

 than the upper one. The inner walls are thin and arched convexly 

 inwards, so as to come into close contact with the assimilatory tissue 

 below. The lateral walls are thin and straight ; the outer walls are 

 flati and greatly thickened. 



