CUTTING SECTIONS 7 



excessively (as in many Algse) to use solutions of picric, chromic, 

 or osmic acids, to which an equal volume of absolute alcohol 

 has been added. 



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 longi- 

 tudinal planes which do not include the organic axis. 



This may be illustrated by a diagram (Fig. 1), which 

 may be taken to represent the transversely cut end of 

 a cylindrical stern, the tissues being arranged with re- 

 ference to a central point (E) : transverse sections are 

 those which are in transverse planes, parallel to the 

 plane of the paper in Fig. 1. The line including the 

 central points of successive imaginary transverse sections 

 is the organic axis. 



Radial and tangential sections are both in planes 

 vertical to that of the paper in Fig. 1 : a radial section 

 (A E B) includes the organic axis (E), and a slice of 

 tissue thus cut when examined from a direction indi- 

 cated by either of the arrows (x) will show in surface 

 view those cell- walls which run radially : a tangential 

 section (c D) does not include the organic axis (E), and 



