CHAPTER VI 



SECTION?, HOW TO PREPARE AND EXAMINE THEM 



Sections. To fully investigate the internal structure of a 

 plant or its members, it is necessary to cut sections of the plant 

 in various directions. A piece cut out of a stem is called a 

 section. If the stem is cut across at right 

 angles to its long axis it is called a trans- 

 verse section. When the stem is cut along 

 its long axis, the section made is termed 

 longitudinal. There are two kinds of 

 longitudinal sections, radial and tan- 

 gential. A radial longitudinal section 

 is one which passes through the organic 

 centre of the stem. A tangential section 

 can be made lengthways through the 

 stem, but does not pass through the cen- 

 tre. This is illustrated by Figs. 78, 79, 80 

 and 8 1. When a piece is cut out of a 

 stem in the plane A, Fig. 78, the section 

 is transverse. Such a section is shown in 

 Fig. 79. If the cut is made through B, 

 Fig. 78, it passes through the organic 



centre, and is a radial longitudinal section, as shown in Fig. 80. 

 The tangential section can be made through the plane C, Fig. 78. 

 This is shown in Fig. 81. 



To make good sections either a very sharp knife or a razor 

 will be necessary. The shape of the blade will depend upon the 

 size of the proposed section ; if the area of the section is small, 

 a hollow-ground razor or knife will give the best results, but for 



FIG. 78. Diagram illus- 

 trating how to cut sec- 

 tions. A cut along the 

 line A gives a transverse 

 section : along plane B, 

 a radial section : and 

 along C, a tangential 

 section. 



