Betts. — Autecology of Plants of Peridotite Belt, Nelso?i. 311 



The chlorencliyma forms a compact mass, and in the centre of it there 

 is some aqueous tissue which consists of very large roundish cells with very 

 thin cell- walls. 



Fig. 41 shows a transverse section of the margin of the leaf. The cuticle 

 is very thick. The cells of the upper epidermis are slightly elongated at 

 right angles to the surface of the leaf, and have thickened walls, and the 

 cells of the lower epidermis are smaller and are squarish. Beneath the 

 epidermis there is a hypoderma composed of 1 or 2 layers of cells with 

 thickened, lignified cell-walls. The rest of the margin is occupied by a 

 large mass of sclerenchyma, the cells of which have their lumen almost 

 obliterated. 



• 38. Libertia ixioides Spreng. 



Habit. — A perennial herb with a short creeping rhizome and long fibrous 



roots. The leaves are numerous, densely crowded, linear, flat, rigid, and 



arranged in two vertical series (distichous). The margins are cartilaginous 



and smooth. . 



^ Anatomy. 



Leaf (figs. 44-47). — Fig. 44 shows diagrammatically a view of half the 

 transverse section of the leaf. From this it will be seen that the vascular 

 bundles are arranged in two series, one along each face of the leaf ; that 

 the bundles are opposite, and that each is surrounded by a mass of 

 sclerenchyma. 



Figs. 45 and 46 show in more detail the structure in transverse section. 



The epidermis is composed of small, squarish cells, all the walls of which 

 are thickened, and there is' also a thick cuticle. 



Stomata are found on both surfaces, and they are fairly frequent. 

 The guard-cells are sunken right below the epidermis, and they have 

 thickened cell- walls. The stoma is therefore at the bottom of a pit. 



The chlorenchyma consists of large, roundish cells with somewhat 

 thickened cell-walls and containing numerous chloroplasts. This tissue 

 is fairly compact, so that there are only small intercellular air-spaces. 

 Beneath each stoma, however, there is a fair-sized air-space. 



The vascular bundles are of the usual monocotyledonous type, and all 

 the xylem elements are lignified. Surroimding each vascular bundle there 

 is a mass of sclerenchyma ; this is composed of small roundish cells with 

 thick cell- walls. 



The central part of the leaf is occupied by a colourless tissue formed of 

 large cells with slightly thickened cell-walls, and with small air-spaces 

 between the cells. This tissue forms an aqueous tissue. In some parts 

 the cells lying between the two opposite masses of sclerenchyma have 

 lignified cell- walls. 



Fig. 46 shows a transverse section through the margin of the leaf, which 

 is thickened. The cuticle here is thicker, and the epidermal cells are some- 

 "what larger, and their external cell- walls are thicker than near the centre 

 of the leaf. Under the epidermis there is a single layer of cells which con- 

 tain a few chloroplasts. The rest of the space is occupied by a large mass 

 of sclerenchyma, composed of cells with a very small lumen. In the centre 

 of this mass there is a small vascular bundle. 



Peduncle (fig. 48). — The epidermis is composed of small cells with all 

 their walls, and especially the lateral walls, very much thickened. A cuticle 

 is present, but it is not so thick as in the leaf. 



Stomata are not frequent ; £he guard-cells have thickened cell-walls 

 and are but slightly sunken, so that they are not at the bottom of a pit as 

 in the leaf. 



