Double-stained Hand Section of Root 211 



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 12) of holding them either in pieces of pith or between the 

 cut halves of a carrot. If the sections are cut by hand, they may be trans- 

 ferred 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 jjl thick. 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 alcohol for the removal of 

 the xylene, and thence graded down through alcohols to water. By what- 

 ever method the sections are produced, they are accumulated in a small 

 dish of distilled water. These sections, of course, will retain the cell con- 

 tents, which must be removed in order that the sections may be turned 

 into true skeletons. 



The best reagent to use for skeletonizing sections of plant tissue is either 

 potassium or sodium hypochlorite. Ordinary "bleaching solutions" sold 

 for household purposes under various trade names are not suitable since 

 they contain large quantities of calcium hypochlorite. If, however, the 

 pure salts are not available, the household solution may be employed by 

 adding to it enough of a solution of potassium or sodium carbonate to 

 precipitate the calcareous contents and by filtering off the solution before 

 use. If the pure salts are available, a 1 per cent solution may be employed 

 conveniently. The sections are removed from the distilled water on a sec- 

 tion lifter and transferred to a watch glass of the sodium or potassium 

 hypochlorite solution. If the sections are made from material that has 

 been preserved in alcohol, this solution should be used cold, but usually 

 it must be warmed if it is to have the desired effect on materials that 

 have been resurrected from a dried condition. In either case the operation 

 should be watched very carefully under a low power of the microscope, 

 and the action of the hypochlorite should be discontinued as soon as the 

 cells are seen to be free of their contents. If the mounter is completely 

 inexperienced in this field and is unable to determine the point at which 

 the operation should be stopped, it is recommended that a single section 

 be taken and the skeletonizing followed under a microscope while it is 

 timed. It will be seen that when the operation has gone too far the finer 

 cell walls present will be dissolved by the solution. If the period at which 

 the first of the cell walls dissolves is carefully recorded and one-half of 

 this time taken for the subsequent sections, these will be cleaned perfectly 

 without the slightest risk of damage to their walls. After they are removed 

 from the hypochlorite solution, the sections should be washed thoroughly 

 in several changes of distilled water and then passed into a solution of 1 

 per cent acetic acid, where they are rinsed several times and then re- 



