154 XEROPHILOUS CHARACTERS OF HAKEA DACTYLOIDES^ 



siDaces here either. These cells do not contain so much chlorophyll 

 as the palisade cells. 



All through the mesophyll are numbers of large scleroblasts or 

 stone-cells, columnar and simple (Fig. 8), or massive and irregu- 

 larly branched in all directions (Fig. 9). Occasionall}^, a detached 

 cell is found among the palisade cells, but the greater number have 

 one or more of their branches touching the inner wall of the epider- 

 mis, and this part is usually expanded as if it were soft, and press- 

 ing against the epidermis. The greatest axis of these cells is at 

 right angles to the j^lane of the leaf. They only rarely pass into 

 the central region of the mesophyll, and still more rarely extend 

 through from one palisade layer to the other. In some of them, a 

 central cavity is seen, very narrow and branching, but the branches 

 do not always correspond to the arms of the cell (Figs. 8 and 9 a). 

 There are also narrow openings in the thickened wall, leading- 

 straight in to the central cavity. 



The vascular bundles have a very strong development of hard 

 bast — sclerencbymatous fibres with thick walls and small lumina. 

 The few spiral vessels and sieve-tubes are embedded in the centre 

 of this. In the marginal vein, the fibres lie outside the veins? 

 but not inside. 



The foregoing description applies to mature leaves growing in 

 the open. Plants growing in shady places show marked differ- 

 ences. The leaves of the plants in the open average 04 mm. in 

 thickness, while those of shade-plants are only 0-3 mm. The fol- 

 lowing table shows the main differences in measurements between 

 ordinary and shade-leaves. 



In the shade-leaves, each cell of the epidermis almost always con- 

 tains a single cubical crystal. The stomates are fewer in number 



