92 PEACTICAL BOTANY. 



Good sections may be obtained by holding the piece of lamina 

 between slices of carrot, or pith ; or by folding the whole lamina 

 repeatedly, and cutting sections from the whole mass. In these 

 cases, though the chlorophyll appears of a better colour, the 

 sections not having been treated with a solvent (alcohol), still 

 the sections are infested with air bubbles, which may be partially 

 removed by leaving the sections for some minutes in water ; 

 they may be completely removed (though the chlorophyll 

 would be dissolved) by treatment with alcohol. Difficulty will 

 often be found in obtaining good preparations of the above ; all 

 the important points may be more easily observed in the Cherry 

 Laurel. 



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 appear- 

 ing semilunar, as in the petiole. The convex side 

 is the inferior (dorsal), and the concave the superior 

 (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 com- 

 plicated. 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 



