SECTION-CUTTING. 



99 



thinnest possible slice may be taken off by the knife ; after 

 a few thick slices have been removed to make the surface 

 level, a small quantity of water or spirit may be placed 

 upon it; the screw is then to be turned one or more 

 divisions, and the knife passed over the wood until a slice 

 is removed; this, if well wetted, will not curl up, but will 

 adhere to the knife, from which it may be removed by 

 pressing blotting-paper upon it, or by sliding it off upon 

 a piece of glass by means of a wetted finger. The plan 

 generally adopted is to have a vessel of water by the side of 

 the machine, and to place every section in it : those that 

 are thin can then be easily separated from the thick by 

 their floating more readily in the water; and all that are 

 good, and not immediately wanted, may be put away in 

 bottles with spirit and water, and preserved for future 

 examination. If the entire structure of any exogenous 

 wood is required to be examined, the sections must be 

 made in at least three different ways; these may be 

 termed the transverse, the longitudinal, and the oblique, 

 or, as they are sometimes called, the horizontal, ver- 

 tical, and tangental : each of these will exhibit different 



Fig. 68. Sections of Wood. 



appearances, as may be seen upon reference to fig. 68 : 

 b is a vertical section through the pith of a coniferous 

 plant : this exhibits the medullary rays, which are known 



H2 



