PRACTICAL BOTANY 



produces an excessive blackening of the cells, which can be 

 removed by treatment with chlorine-water. 



Of the hardening reagents above mentioned absolute alcohol, 

 methylated spirit, and picric or chromic acids are those most 

 generally used. 



III. Cutting Sections. In order to investigate the structure 

 of the tissues of a plant or member, it is usually necessary to 

 cut sections, i.e. thin slices, in various directions. To make a 

 complete study of a solid mass of tissue, sections must be 

 cut in three different planes at right angles to one another. 



Taking the case of a cylindrical stem, the best way to study 

 its structure would be to cut 



(i.) Transverse sections, in planes at right angles to the 

 organic axis. 



(ii.) Radial longitudinal sections, in longitudinal planes 

 including the organic axis. 



(iii.) Tangential longitudinal sections, in longitudinal planes 

 which do not include the organic axis. 



This may be illustrated by a diagram (Fig. i), which may be 

 taken to represent the transversely cut end of a cylindrical 

 stem, the tissues being arranged with reference to a central 

 point (E) : transverse sections are those which are in transverse 



