INTRODUCTION 6 



may be cut free-hand with a sharp pocket-knife or razor and 

 mounted in water. To avoid air bubbles in the sections small 

 pieces of the specimens should be boiled prior to sectioning. 

 It is not important that such sections be of uniform thickness, 

 since a thin edge will usually exhibit the essential details. 



Much better results can be obtained by the use of a microtome. 

 Penhallow recommends a table microtome and a plane blade 

 mounted in a heavy wooden handle of such a form as to provide a 

 perfectly firm grip. For fine work, however, a sliding microtome 

 specially constructed for sectioning wood is best. Success depends 

 largely upon the sharpness of the knife and the rigidity of the 

 apparatus. 



Considerable care should be exercised in the selection of 

 material for sectioning. Small blocks of about a quarter-inch cube 

 should be cut from green material, or from the interior of dry 

 pieces. The faces of the blocks should represent sections which 

 are as nearly cross, radial, and tangential as possible. Blocks of 

 the lighter woods can be softened sufficiently by boiling them in 

 water until thoroughly saturated. The process may be hastened 

 by interrupting the boiling by additions of cold water. In the 

 case of the harder woods, however, it is a good plan to place 

 the small blocks, after boiling, in a solution of hydrofluoric acid 

 for a period varying from ten days to three weeks, the strength 

 of solution and the duration of immersion depending upon the 

 hardness of the wood. After removal from the acid the blocks 

 should be thoroughly washed and then placed for several days in 

 glycerine, after which they are ready for sectioning. The sections 

 may either be mounted unstained in glycerine or stained in the 

 usual way and mounted in balsam. For ordinary work unstained 

 glycerine-mounts afford the most satisfactory results, since the 

 natural colors are preserved. (For more detail, see references 

 below.) 



References 



Bailey, I. W.: Microtechnique for Woody Structures, Bot. Gaz., Vol. XLIX, 



Jan. 1910, pp. 57-58. 

 Plowman, A. B. : The Celloiden Method with Hard Tissues, Bot. Gaz., Vol. 



XXXVII, June 1904, pp. 456^61. 

 Penhallow, D. P. : North American Gymnosperms, Boston, 1907, pp. 16-23. 

 Benedict, H. M.: An Imbedding Medium for Brittle or Woody Tissues, 



Bot. Gaz., Vol. LII, Sept. 1911, p. 232. 

 Thompson, R. B.: A Modification of a Jung-Thoma Sliding Microtome for 



Cutting Wood, Bot. Gaz., Vol. L, Aug. 1910, pp. 148-149. 



