126 PRACTICAL BOTANY 



Note with a low power 



1. The general outline of the section, which is 

 irregular and undulating, though it is in the main of 

 uniform breadth. At the point corresponding to the 

 main nerve the section widens out, the nerve appearing 

 semilunar, as in the petiole. The convex side is the 

 inferior (anterior or dorsal), and the concave the 

 superior (posterior or ventral) surface. 



2. That the margins of the sections (i.e. the superior 

 and inferior surfaces of the leaf) are studded with 

 projecting multicellular hairs. 



3. That the arrangement of the tissues in the large 

 nerve resembles that in the petiole, though less compli- 

 cated. Thus it often has but one large central bundle, 

 with smaller lateral ones. The position of the xylem 

 and phloem relatively to the whole leaf corresponds to 

 that in the petiole, i.e. xylem towards the upper surface, 

 phloem towards the lower. 



Occasionally some of the smaller bundles in the vein are in- 

 verted, showing an approach to the arrangement of bundles in the 

 polysymmetrical stem. 



4. Smaller veins, with correspondingly reduced 

 vascular bundles, are found scattered through the 

 thinner part of the section. 



Next examine the thinner part of the section with a 

 high power, and, starting the study of them from the 

 upper surface, note successively the following tissues : 



1. Upper layer of epidermis, continuous with that 

 covering the nerve : it is a single layer of cells, covered 

 externally by cuticle, which has the same characters 

 as that of the stem. The epidermis bears numerous 



