12 THE JOUKNAL OF INDIAN BOTANY. 



The peculiar isobilateral structure of the wood of G. varians is 

 due to the fact that portions of the axis with greater development 

 of wood represent the plane affected by the prevailing wind and 

 possessing greater functional activity ; the two opposite sides of the 

 axis with poorly developed wood represent the plane less affected by 

 the prevailing wind and have no necessity of developing an extensive 

 water-conducting or strengthening tissue. The plane with well 

 developed wood represents the direction of the prevailing wind. The 

 wood parenchyma is not extensive and is found on the inner side of 

 the wood ring. 



The soft bast is very extensive in P. cynanchoides. 



The pith consists of thin-walled cells. Some of the pith cells of 

 S. brcvisligma contain spherical granular bodies. 



General Review. — The epidermal cells have the outer walls greatly 

 thickened. The guard-cells are situated in the same plane or quite 

 below the plane of the surrounding colls. The stomata are accom- 

 panied by subsidiary cells. The ventilating system is fairly extensive. 

 Secretory cells with tanniniferous contents are found in some 

 members. Oxalate of lime is found in the form of small clustered 

 crystals in P. cynanchoides. Hairs, when present occur in the form 

 of short uniseriate trichomes. Cortical parenchyma is extensive. 

 The pericycle is either composed of groups of stone-cells or of bast 

 fibres. The wood forms a composite hollow cylinder. Perforations 

 of the vessels are simple. The wood prosenchyma is composed of 

 cells with thick walls and with small lumina. The medullary rays 

 are 1 — 3 seriate. Pith consists of thin-walled cells. 



GENTIANACEAE 



Enicostemma litorale BL— Fig. 201. Epidermal cells with 

 outer walls very greatly thickened and with inner walls convexly 

 arched inwards. Lateral walls thin and undulated. Stomata on 

 both the surfaces elevated Mesophyll wholly of chlorenchyma. 

 Internal glands absent. Oxalate of lime in the form of star-like 

 clusters of acicular crystals. Leaves many-ribbed. Veins of ribs 

 vertically transcurrent. Vascular bundles in leaf and axis bicol- 

 lateral. Axis irregularly ribbed. Scleranchymatous pericycle absent. 

 Cortex formed of chlorenchyma. Wood composite with an outer 

 and inner ring of soft bast. Vessels in numerous complete rows. 

 Medullary rays uniseriate. Pith of thin-walled cells. 



Structure of the Leaf. — The epidermis consists of polygonal cells 

 with outer walls very greatly thickened (fig. 201). The lateral walls 

 are thin and undulated. The inner walh are. thin. The cuticle is 



