AS AIDS IN THE DETERMINATION OF SPECIES. 9 



The outer wall is moderately thickened to prevent excess of evaporation, and 

 generally to provide against injury. In the ordinary unstained cell there may be 

 distinguished outside of the round or oval cell cavity a distinct clear band externally, 

 and a somewhat turbid-looking portion abutting on the cell cavity. As the outer 

 band is coloured a pale yellow by Schulze's solution, it represents a cuticle, which is 

 continued right round the section, forming a slight convexity on the outside of each 

 cell. It is on an average from l-3200in. to l-2400in. in thickness, and shows no 

 sign of striation. 



The turbid-looking portion of the wall is coloured a deeper yellow by Schulze's 

 solution, and may even pass into orange-yellow or pale crimson, according to the 

 amount of colouring matter present. Hence it may be concluded that beneath the 

 fine sheet of cuticle, which is of the nature of cork, there is a cuticularised layer, a 

 sort of transition between cellulose on the one hand and cuticle on the other. The 

 use of the cuticle and cuticularised layer is evident, principally for the purpose of 

 preventing evaporation. It is very thick on desert plants. Plants in rainless regions, 

 and Australian plants generally, are well provided with it. The sections of the 

 Mallee scrub species, to be afterwards referred to, will show this clearly. 



The lateral walls unite the cells together, and are relatively thin. They 

 terminate outwardly at the cuticle, and leave no gaps between. No contrivances for 

 admitting air were found, although carefully looked for. The inner wall is likewise 

 thin, and may be composed of cellulose, being coloured purple by Schulze's solution, 

 thus allowing nutritive substances to pass in and nourish the living cell. Or it may 

 be, like the outer wall, coloured yellow, and thus cut off from nutritive supplies, so 

 that no further growth or expansion can take place. In the one case the epidermal 

 cell is living, and capable of further growth, in the other it has reached maturity, 

 and become surrounded by a corky wall. 



From the relative thickness and breadth of each epidermal cell, it may be 

 inferred that it has the form of a prism perpendicular to the surface, and the cuticle 

 covering produced by each, forms a continuous layer all round the outside. 



2. Cortical Tissue, or starch-manufacturing tissue principally. — Immediately 

 beneath the epidermis there is a single layer of cells, which may or may not have 

 their outer and lateral walls cuticularised, and which form a more or less distinct 

 outer border to the cortex proper. This may be called the Hypodermal layer 

 (Fig. 2). 



The remaining cells are of irregular outline, with walls of various degrees of 

 thickness. The cortical parenchyma contains chlorophyll, and it is here the 

 manufacture of starch is carried on, as evidenced by the contents of the cells 



