126 Methods in Plant Histology 



any staining. Large sections of cornstalk are rather hard to cut, 

 because the rigid bundles tear through the soft parenchyma. Flood- 

 ing with 95 per cent alcohol facilitates the process. A slight harden- 

 ing is sufficient, so that about 4 or 5 sections can be cut in 1 minute. 



STONY TISSUES 



Sections of the stony tissues of hickory nuts, walnuts, peach 

 stones, and similar refractory substances cannot be cut by ordinary 

 methods. 



With a fine saw, saw sections about 1 mm. in thickness. Rub 

 a section between two pieces of fine sandpaper until it is not more 

 than half a millimeter in thickness. Then rub it between two smooth 

 hones, keeping the hones wet with water. When the section is thin 

 enough, wash it thoroughly in water, using a pipette to rinse off any 

 particles of dirt. Dehydrate in absolute alcohol, clear in clove oil, 

 and mount in balsam. The long, narrow pores show better without 

 any clearing. In this case, dry the section thoroughly, heat a few 

 drops of balsam on the slide to drive off the solvent, put the section 

 into the balsam, and add a cover. The air caught in the long, narrow 

 pores will make them appear as black lines. Sections of most nuts 

 show excellent detail without any staining. Thin sections, however, 

 may be stained in the usual way. 



PETRIFACTIONS 



During the past ten years the study of fossil plants has made 

 even more rapid progress than during the previous decade. Scarcely 

 any problem involving the anatomy of living vascular plants can be 

 investigated intelligently without some knowledge of Paleozoic and 

 Mesozoic forms. Consequently, it is becoming increasingly neces- 

 sary for laboratories to have apparatus and technic for cutting rock- 

 sections. 



The outline of the process of cutting a rock-section is very simple: 



1. Saw the rock into two pieces. 



2. Polish the cut surface. 



3. Fasten the cut surface to a piece of glass with hot shellac. 



4. With the saw, make another cut, as close to the glass as possible, 

 so as to leave a thin section firmly fastened to the glass. 



