Example 9 



Preparation of a Transverse Section of a Root, Using the 

 Acid Fuchsin-iodine Green Technique of Chamberlain 



This is the simplest of all the preparations which is described in this part 

 of the text, and can be recommended unhesitatingly to the beginner who has 

 never previously prepared a section of any type. This preparation is designed 

 to show only the skeletal outlines of the cells and is not intended to demon- 

 strate in any way their cytological contents, which are removed in the course 

 of preparation. If cytological detail in a botanical section is required, a paraffin 

 section should be prepared and stained by the method given in Example 11. 



It does not matter from what source the root is obtained, but it is recom- 

 mended that the beginner select some soft root of about an eighth of an inch 

 or somewhat less in diameter. If the root is collected from a living plant, it 

 should be washed thoroughly to remove any adherent sand grains, which will 

 spoil the edge of the cutting knife, and then preserved in 96 per cent alcohol 

 until required. The 96 per cent alcohol should be changed as it becomes dis- 

 colored, but with this precaution the specimens may be preserved indefinitely. 



It is even possible to make preparations of this type from dried roots which 

 have been preserved in a herbarium. The best method of swelling and soften- 

 ing these dried preparations is a 10 per cent solution of phenol in lactic acid. 

 The lactic acid employed is the ordinary commercial solution in which the 

 phenol should be dissolved immediately before it is required. Pieces of the 

 dried root are placed in a reasonably large volume of this material and heated 

 over a low flame to a temperature of about 50° C. Within 10 or 15 minutes 

 a completely dried herbarium specimen will have become swollen out to its 

 normal size and softened to the extent that sections may be cut readily from it. 



The method of sectioning selected does not particularly matter. Since the 

 sections cannot in any case be subjected to the first process while they are 

 attached to the slide, there is no real advantage in embedding in paraffin and 

 cutting in this medium if an ordinary hand microtome is available from which 

 sections can be taken by the conventional method (see Chapter 8) of holding 

 them either in pieces of pith or between the cut halves of a carrot. If the sec- 

 tions are cut by hand, they may be transferred immediately after they are cut 

 to a dish of 20 per cent alcohol and from there to water; if they are cut in 

 paraffin, they should be at least 20 microns in thickness. The ribbon, as it is 

 removed from the microtome, should be dropped directly into a watch glass 

 of xylene in which the paraffin will dissolve readily. The individual sections 

 are then removed from the xylene with a section lifter, passed through absolute 



106 



