PLANTS OF THE INDIAN DESEET. 245 



Hairy covering consists of unicellular curved hairs with perhaps 

 a function of absorbing water. Walls are thin and superficially 

 knobbed. Glandular hairs are not found in the leaf and axis. 



Structure of the Axis : —The epidermal cells are small with outer 

 walls thickened and papillose. The primary cortex is formed of 

 chlorenchyma. 



The perioycle forms a more or less composite ring of stone- 

 cells. The wood is composite. Vessels are large and few ; they are 

 more abundant in the inner half of the wood. Interfascicular wood 

 prosenchyma is extensive. Wood parenchyma is more abundantly 

 developed than in Papilionaceae and enclose the inner ends of the 

 xylem bundles. The medullary rays are unseriate. 



The pith consists of small cells with thickened and lignified walls. 



MIMOSEAE 



Acacia Senegal, Willd. —Figs, 120, 121. Epidermal cells with 

 outer walls thickened and papillose. Stomata occurring on both the 

 surfaces. Mesophyll formed of palisade tissue on the upper side and 

 of arm-palisade tissue on the lower. Tannin sacs present in the leaf and 

 axis. Veins embedded. Clothing hairs unicellular. Cork subepider- 

 mal. Pericycle forming a composite ring of stone-cells. Small groups 

 of stone-cells in soft bast. Vessels large. Medullary rays uniseriate. 

 Pith composed of cells with thick and lignified walls. 



Structure of the Leaf: — The epidermal cells have outer walls 

 thickened and papillose. Stomata occur on both the surfaces. The 

 guard-ceils are situated in the plane of surrounding cells and the front 

 cavity is placed in a depression formed by the papillose outer walls 

 of the epidermal cells. 



The mesophyll is composed of 3-4 layers of palisade cells on 

 the adaxial side and of arm-palisade tissue on the abaxial side. The 

 middle tissue consists of a layer of large parenchymatous cells with 

 tanniniferous contents. Internal secretory organs are represented 

 by tannin sacs occurring in the middle of the mesophyll, in cortex 

 and pith. 



The veins are embedded. The veins of the mid-rib are protect- 

 ed on the lower side by strands of sclerenchyma. 



The hairy covering consists of a few unicellular clothing hairs. 

 Glandular hairs are not found. 



Structure of the Axis: — The cortex is characterised by subepi- 

 dermal cork. Some of the cells of the tanniniferous cortical 

 parenchyma near the pericyclic stone-tissue contain solitary crystals 

 of oxalate of lime. 



19G8— 33 



