PALEOBOTANICAL MICROTECHNIQUE 157 



ing, even if it should be necessary to heat it a Httle to make it flow 

 well. 



By this method, sections of fossils 10X15 cm. have been cut thin 

 enough for examination with a 4 mm. objective. Sections 3 or 4 mm. 

 square have been cut thin enough for satisfactory examination with a 

 2 mm. oil immersion lens. Figure 28 shows that a rehable study can be 

 made from sections cut from the solid rock. 



Of course, this method can be used for such objects as walnut and 

 hickory shells. 



It is not really necessary to cover the section. Just polish the sur- 

 face with fine carborundum and then polish still smoother with a fine 

 powder of tin oxide. The section will look as if mounted in balsam. 



A fine view can be secured without making any section. Merely 

 polish the cut surface as described in the preceding paragraph and ex- 

 amine by reflected light. Excellent photomicrographs can be made from 

 such surfaces. 



PEELS 



Peels seems to be as good a name as any for a type of "section" 

 which is saving the paleobotanist a lot of time and is making possible 

 a near approach to serial rock-sections. Peels are made with celloidin 

 or with gelatin. 



Celloidin peels. — Probably every investigator has his own method 

 of making a celloidin peel. The following method, written by Dr. 

 Fredda Reed, applies to calcified petrifactions: 



1. After cutting a coal ball in two, polish the surface of the petrifaction 

 with fine carborundum powder. 



2. Wash surface. 



3. Treat with 5 per cent hydrochloric acid 2-5 minutes. The thickness of 

 the plant tissue peeled depends upon the length of the acid treatment. 



4. Wash gently in running water. 



5. Dry. 



6. When thoroughly dry support the rock in a horizontal position and 

 pour over the surface a solution of equal parts of absolute alcohol and 

 ether quickly (before the alcohol-ether solution has had time to 

 evaporate) : 



7. Pour on 25 per cent celloidin (dissolved in equal parts of absolute 

 alcohol and ether). 



8. Peel. When the absolute alcohol and ether have evaporated, the cel- 

 loidin is left as a thin film which may be peeled off by inserting a 

 scalpel under the edge. 



