140 APPENDIX 



inuiuitiiig .sueli sections in a weak .sululion of aleuliol. This may 

 act as a Ivilling reagent for the protoplasm but it does mal^e pos- 

 sible the accurate study of the shape, arrangement and character 

 of the walls of cells. 



Prepared Slides 



The use of permanent slides is essential in the study of many 

 of the topics outlined in this book. This is particularly ti'iie for 

 the work to be done under Exercises III, X, XII. XIII. and 

 XIV. Suitable preparations as a basis for class study are obtain- 

 able from commercial supply houses or may be prepared for the 

 student directly. With reference to the latter possibility, detailed 

 suggestions for the collection, fixation, sectioning, and staining 

 of tissues and organs are presented systematically in the I'eeent 

 manuals on microtechnique by Johansen (1940) and Sass (1940). 



Macerated Tissue 



One of the most important skills which the student must 

 develop in laboratory practice is the ability to visualize cells as 

 three-dimensional bodies. This is often extremely difficult on the 

 basis of the examination of sections which tend to create a two- 

 dimensional concept. Furthermore, many definitive features of 

 cells, particularly the structure and arrangement of pits and 

 fibrous thickenings in traeheary elements, and the character of 

 perforations in vessel elements, can best be studied in isolated 

 cells. For these reasons, a study of macerated tissue is recom- 

 mended for many topics in this Ijook and is especially d(»sirable 

 in connection Avith Exercises II, VIII. IX, and X. The macera- 

 tion of plant tissue is most effectively accomplished by the use 

 of certain reagents which dissolve the intercellular substance and 

 thus cause the sei)aration of a piece of tissue into its comp(ment 

 cells. Jeffrey's method is usually satisfactory. Sm<dl i)ieces of 

 the material, no thicker than a match, are placed in a glass vial 

 containing a mixture of equal parts of lO'^f clu'omic jicid and 

 10% niti-ic acid. The vial is then coiked and ])Iac('d in an elec- 

 tric oven at a teini)erature of .■}0°-40° C. until the material 

 becomes soft or *'mushv" in tcxinro. llai-d material, such as 



