174 PKACTICAL BOTANY 



between the two epidermal layers. Compare the 

 phyllodes of Acacia (pp. 135). 



3. The spaces between the tissues hitherto con- 

 sidered are filled with parenchyma (mesophyll), 

 which may either be (a) green (containing chlorophyll), 

 or (b) colourless (without chlorophyll). 



a. The green chlorophyll-containing parenchyma 

 fills up the greater part of the space ; intercellular 

 spaces occur in it. 



I. The colourless parenchyma occurs (i.) as a sheath, 

 without intercellular spaces, surrounding each bundle 

 (bundle-sheath) ; (ii.) as groups of cells immediately 

 below the epidermis : these are more common towards 

 the central part of the leaf. At the midrib this tissue 

 forms the bulk of the structure. 



III. Cut transverse sections of the leaf-sheath, and 

 treat as the above. Compare the arrangement of 

 tissues with that of the lamina, and of the stem. Note 

 that colourless parenchyma preponderates. 



IV. Cut thin tangential sections from the under 

 surface of the lamina, so as to remove, if possible, only 

 the epidermis. Treat with potash, and mount in 

 glycerine. Observe 



1. The ordinary cells of the epidermis, of oblong 

 form, and with sinuous outline. 



2. Short cells between the ends of these, which 

 often project perpendicularly to the surface as hairs 

 of various form. 



3. The stomata, holding the same position as (2) 

 relatively to the oblong epidermal cells. 



Observe with a high power the structure of the 

 stomata. They consist of 



