180 PEACTICAL BOTANY 



directed towards the nearest external surface, the xylem 

 towards the centre. 



Compare the structure of the phyllode of Acacia (p. 

 134). 



iii. LEAF AQUATIC TYPE. 



Cut transverse sections of the leaf of Elodea : fresh 

 material may be used, and the sections may be mounted 

 in water. On examination the flattened lateral portion 

 of the leaf will be found to consist of two layers of cells, 

 with intercellular spaces, but no stomata. The upper 

 layer consists of larger, the lower of smaller cells, and 

 both contain chlorophyll. 



Note the thicker midrib, and reduced vascular 

 bundle, which consists of two or three fibres of bast 

 towards the lower surface, while towards the upper 

 surface a small-celled tissue is all that represents the 

 xylem. 



EOOT. 



I. Cut transverse sections of the root of the Maize, 

 selecting a well-grown, underground piece of root : 

 mount in glycerine, and examine first under a low 

 power, then under a high power. Starting from the 

 periphery observe 



1. The superficial piliferous layer, consisting of 

 small cells, many of which have grown out into long 

 root-hairs. 



2. Immediately below this is a protective layer of 

 exodermis, with more or less cuticularized cell-walls, 



3. The cortical parenchyma, a broad band, of 



