PLANTS OF THE INDIAN DESERT. 285 



The wood is composite in all members. In species of Trian- 

 thema it is composed of numerous xylem bundles which are 

 embedded in interfascicular wood prosenchyma in more or less 

 distinct concentric rings (figs. 140, 143). In species of Mollugo it is 

 composed of large xylem bundles with vessels large and numerous and 

 with little interfascicular wood prosenchyma (figs. 149, 153, 155). 

 Vessels, in 0. decumbens, G. phamaceoides and L. indicum, are large 

 and numerous and are uniformly distributed in the interfascicular 

 wood prosenchyma. Thus the structure of the wood can be classified 

 into three types — M, nudicaulis and M. Cerviana representing one type 

 species of Trianthema another and 0. decumbens, M. hirta, G. phama- 

 ceoides and L. indicum the third type. 



The structure of the wood has undergone modifications 



(1) either due to the decumbent habit as in 0. decumbens in 



which the wood cylinder is very much narrowed and the 

 vessels are few and small on the lower side of the axis. 



(2) or to the direction of the prevailing wind as in T. triquetra, 



G. phamaceoides and L. indicum, in which larger xylem 



bundles with vessels larger and more numerous occur on 



two opposite sides of the axis which represent the plane 



of the direction of the prevailing wind, while in a plane at 



right angles to this occur much smaller xylem bundle with 



vessels much smaller and less numerous. 



These modifications are the result of greater functional activity on 



those sides which are more affected by wind in the case of erect axes, 



or by the sun and wind together in case of prostrate axes. 



The pith consists of thick-walled calls in T. pentandra, M. hirta 

 and L. indicum; in other members it is formed of thin-walled cells. 



Oxalate of lime is found in the form of clustered crystals in the 

 cortex and pith of T. triquetra, T. pentandra, 0. decumbens and M, 

 hirta ; in L. indicum clustered crystals occur only in the cortex. 

 Acicular crystals are found in the cortex and pith of G. phamaceoides. 

 Anomolous structures are represented by groups of soft bast 

 embedded in the wood cylinder in T. triquetra. 



General Bevieiu. — 'Epidermis consists of polygonal cells with 

 outer walls usually thickened. Large bladder-like cells with water- 

 storing function are intercalated amongst epidermal cells (figs. 141, 

 143). Stomata are depressed and are accompanied by ordinary 

 epidermal cells. The mesophyll in T. triquetra (fig. 139) is character- 

 ised by an extensive aqueous tissue. Oxalate of lime is found in the 

 form of clustered crystals in the leaf and axis of most of the members. 

 Styloids occur in M. nudicaulis and M. Cerviana; acicular crystals are 

 present in G. phamaceoides. Hairy covering is present only an M. hirta 



2563-37 



