130 PLANT HABITS AND HABITATS IN THE 



mesophyll. There is little mechanical tissue, and what there is consists 

 of cells with prominent lumen, both in connection with the conductive 

 tissue and at the leaf margins. The epidermis is made of two cell- 

 layers of which the walls are fairly heavy. Stomata occur on both 

 leaf-surfaces. An additional feature may be mentioned, namely, the 

 presence of tracheids apparently independent of the regular conductive 

 tissue (fig. 22). Very possibly they may be considered to have the 

 capacity of storing water, as in instances which are well known. 



Gravillea stenobotrya. 

 The leaves of Gravillea stenobotrya are narrow-linear and placed 

 upright on the branches. They have unlike dorsal and ventral 

 sides which are apparently subject to quite similar conditions of light 

 and evaporation. A cross-section of the leaf shows certain striking 

 structural features (fig. 24). The leaf margins are in-rolled, giving 

 a rounded dorsal and a channeled ventral aspect. On the dorsal side 

 the epidermis is especially heavy, owing to the great length of its 

 component cell, and the cuticle also is heavy, but on the ventral side 

 the epidermis is not heavy and the cuticle is light. Few if any trichomes 

 occur on the dorsal surface, while the ventral side is heavily clothed 

 with hairs, all apparently of the two-armed type figured and described 

 by Solereder (1899:803). Stomata are confined to the ventral side. 

 The chlorenchyma is heavier on the dorsal than on the ventral side. 

 Sclerenchyma is associated with the conductive tissue, but is not 

 especially abundant. The ground tissue in the material studied ap- 

 pears to be of a fairly loose structure and is not heavily walled. 



Hakea multilineata and H. leucoptera. 



The leaves of Hakea multilineata are long, narrow, and placed in a 

 vertical position on the shrub. They are striate and have a very 

 tough texture. A cross-section shows that the two sides are similar 

 (fig. 27). The following are the most striking structural features of 

 the leaves: The chlorenchyma extends from side to side. Separating 

 the chlorenchyma into strips are ribbons of sclerenchyma which reach 

 from the fibro-vascular bundles of the middle portion of the leaf to 

 the epidermis of either face. The sclerenchyma appears to be mainly 

 or wholly fibrous. The chlorenchyma is composed of relatively long 

 and narrow palisade cells. The epidermis is heavy and has a heavy 

 cuticle. The stomata are situated at the level of the inner epidermal 

 walls and hence at the bottom of pores made by the thickened outer 

 portion of the epidermis (fig. 28). 



In H. leucoptera the leaves are cylindrical, with the end tapering 

 to a point, hence the common name "needle" bush. The chlorenchyma 

 forms an uninterrupted band beneath the epidermis. The central 

 portion of the leaf has scattering bundles of conductive tissue, each 

 with its accompanying mass of sclerenchyma on opposite sides, 

 and all surrounded by a fairly heavy walled parenchyma. The 



