242 THE JOURNAL OP INDIAN BOTANY. 



Primary cortex is characterised by assimilatory tissue and 

 collenchyma. The assimilatory tissue is formed of palisade cells in 

 C. Burhia ; in others it is chlorenchymatous. The collanchyma 

 is developed in the ribs of the ribbed axis. Eibs are strengthened by 

 sclerenchyma in I. anabaptista, P. odorata and P. trilobus. Cork was 

 not developed in any of the species examined. The endordemis, when 

 differentiated, consists of tabular cells. 



The pericycle is composed of a composite ring of bast fibres in 

 species of Heylandia, Indigo/era, Psoralea and Phaseolus. It forms 

 a composite ring of stone-cells in species of Crotal aria, Tephrosia, 

 Alysicarpus and Bhyncosia. In species of Heylandia and Phaseolus 

 groups of bast fibres are developed along three-fourth of the circum- 

 ference of the axis, while along the remaining portion the pericycle 

 is parenchymatous. This is curious and suggests that the axes are 

 much inclined and that sclerenchyma is developed only on the upper 

 side of the inclined axis. Small groups of bast fibres occur in soft 

 bast of Alysicarpus vaginalis.' 



The perforations of vessels are simple. Size of lumen, abundance 

 and arrangement of the vessels vary in different genera and even in 

 species. These differences may be useful in diagnosis of genera and 

 species, if- due allowance is made for modifications introduced by con- 

 ditions of the soil. 



The vascular system, as a whole, is characterised by the poor 

 development of vessels as regards size and abundance, by abundance 

 of wood prosenchyma and by poorly developed wood parenchyma. 

 These modifications are due to the arrest of the development of 

 parenchyma owing to deficiency of water. A system of well developed 

 water conducting tissue is not required in the axis of desert plants in 

 which all structures are adapted to diminish transpiration. It should 

 be observed that the size and abundance of vessels are usually inverse- 

 ly proportional to each other. 



Soft bast usually forms a continuous ring. It is characterised 

 by the occurrence of tannin sacs in species of Indigo/era, Psoralea 

 and Bhyncosia and by the presence of small groups of bast fibres in 

 A. vaginalis. 



Pith consists of thin-walled cells in species of Heylandia and 

 Crotalaria, I. linifolia, I. argentia, species of Tephrosia, A. vaginalis, 

 P. tribolus and B. arenaria ; and is formed of thick-walled and lignified 

 cells in I. paucifolia, I. anabaptista, P. odorate and B. rhombifolia. 

 Some of the pith cells in I. paucifolia and I. argentia hold tanninifer- 

 ous contents. The pith composed of lignified cells adds to the rigidity 

 afforded by the mechanical tissue ; when it is formed of thin-walled 

 cells it may serve occasionally as an aqueous tissue. 



