286 THE JOURNAL OF INDIAN BOTANY. 



and consists of stellate hairs. There are unicellular papillae-like— 

 structures in L. indicum, (fig. 157), with walls superficially rugose 

 and perhaps with a water-storing function. 



The pericycle is composed of stone-cells, except in species of 

 Trianthema. Wood is composite and can be classified into three types 

 as described already. The structure of the wood undergoes modifi- 

 cations either due to the prostrate habit of the axis or to the action of 

 wind in case of erect axes. The perforations of the vessels are simple. 

 The pith consists of thin-walled or thick-walled cells. 



RUBIACEAE 



Oldenlandia aspera DC— Fig. 162. Epidermal cells with outer 

 walls convexly arched outwards. Mesophyll formed of short-celled 

 palisade tissue. Unicellular dome-like structures with thickened and 

 muriculate walls found on the axis. Epidermal cells of the axis with 

 both outer and inner walls thickened. Internal secretory organs and 

 oxalate of lime not found. Sclerenchymatous pericycle absent. Soft 

 bast of thick walled-cells. T. S. of the axis circular. 



Spermacoce hispida L. — Figs. 160, 161. Upper epidermal 

 cells larger and with outer walls usually toothed in the middle. 

 Mesophyll composed of palisade tissue on the upper side and of spongy 

 tissue on the lower. Internal secretory cells with tanniniferous con- 

 tents numerous in the mesophyll. Secretory cavities found in the 

 mesophyll and cortex. Acicular crystals found in the cortex. Cloth- 

 ing hairs in the form of articulated uniseriate trichomes. Epidermal 

 cells of the axis with outer walls thickened. Axes quadrangular. 

 Angles bearing wing-like ribs. Pericycle forming a loose ring of bast 

 fibres. 



Structure of the Leaf. — The epidermal cells are polygonal with 

 the outer walls greatly thickened and convexly arched outwards. 

 The outer walls of the upper epidermal cells of S. hispida are toothed 

 in the middle, while those of the epidermal cells on both the surfaces 

 in 0. aspera are sometimes papillose. Lateral walls are thin and 

 undulated ; inner walls are thin. 



The stomata are accompanied by subsidiary cells and are more 

 numerous on the lower surface. The guard-cells are situated in the 

 plane of the subsidiary cells which are elevated above the surrounding 

 cells. The front cavity is placed in depressions formed by the outer 

 thickened walls of the surrounding cells. The stomata on the axis 

 have the same characters as of those on the leaf (Gg. 162). 



The mesophyll in 0. aspera is composed wholly of short palisade 

 cells ; it is bifacial in S. hispida. Internal glands occur -only in 

 S, hispida, and are represented by mucilaginous secretory ^cavities 



