PLANTS OF THE INDIAN DESEET. 241 



Tephrosia, Aly sicar pus an d Rhyncosia. The veins are few and do 

 not anastomose freely, which suggests that the leaves do not transpire 

 vigorously. 



The hairy covering consists of clothing and glandular hairs. 

 Clothing hairs are of the nature of uniseriate trichomes and have 

 varied forms as follows : — 



(a) With walb smooth or muriculate as in H. latcbrosa, C. Burhia 

 fig. 100 and species of Tephrosia, Phaseolus and Rhyncosia. 



(b) Terminal cell bent in the form of a hook in A. vaginalis 

 fig. 110. 



(c) Terminal cell bent and lying parallel to the surface and with 

 a muriculate surface in P. odorata fig. 108. 



{d) Two-armed and formed of a stalk cell and of an unicellular 

 two-armed terminal cell, the arms being equal in species of Indigo/era 

 fig. 105. 



The covering of clothing hairs in isobilateral leaves is not dense 

 and it should be noted that two-armed hairs in Indigo/era, though 

 few in number, are short-stalked and form a suitable light screen close 

 to the surface of the leaf, against strong light and glare, which 

 accelerates transpiration and is injurious to chlorophyll. 



External glands are not found on the leaf of species of Heylandia, 

 Crotalaria, Indigofera and Tephrosia. In species of Rhyncosia 

 glandular hairs are formed of a short uniseriate stalk and of a 

 spherical head fig. 114 ; they occur on both the surfaces. External 

 glands in P. odorata and P. trilobus are club-shaped and consist of a 

 short uniseriate stalk and of a head divided by horizontal and vertical 

 walls. Glandular hairs in A. vaginalis are composed of a stalk-cell 

 and a globose head, divided by horizontal and vertical walls ; they 

 occur only on the lower surface of the leaf. 



It should be observed that external glands are found in a small 

 number of species and sometimes only on the lower surface. 



Structure of the Axis: — The epidermis is two-layered in species 

 of Heylandia, Crotalaria and Psoralea; it is single layered in species 

 of Indigofera, Tephrosia, Phaszolus, Alysicarpus and Rhyncosia. 

 The outer walls are thickened and are arched convexly outwards. 



Hairy covering has the same character as of that on the leaf. 

 It should be noted that glandular hairs formed of a multicellular 

 stalk and of an irregularly divided head are found in I. argentea. 



Internal secretory organs are represented by tannin sacs. They 

 are abundant in species of Indigofera and occur in the cortex and 

 pith. Some of the vessels in I. liniflolia also hold tanniniferous 

 contents. Tannin sacs occur in the soft bast of species of Psoralea 

 and Rhyncosia. 



