CHAPTER XIII 

 PALEOBOTANICAL MICROTECHNIQUE 



During the past three or four years, new methods in paleobotanical 

 microtechnique have greatly minimized the drudgery of making prepa- 

 rations for microscopic examination. The subject of paleobotany has 

 been making such rapid progress that scarcely any problem involving 

 the anatomy of living vascular plants can be investigated intelligently 

 without some knowledge of Mesozoic and Paleozoic forms. Material, 

 especially that of Paleozoic pteridophytes and gymnosperms, is be- 

 coming available in the United States, largely through the discoveries 

 of Dr. Noe and his students. Consequently, it is increasingly necessary 

 for laboratories to have apparatus and technique for making rock- 

 sections. 



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 mth 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. 



5. Grind and polish until the section is as thin as possible, or as thin as you 



want it. 



6. Wash all polishing powder off \\ath water. 



7. Dry completely and, either with or ^^^thout moistening in xylol, mount 

 in balsam. 



A word of suggestion in regard to these various points may not be 



amiss. 



1. Most rock-sections are cut with a rather expensive and quite 

 compUcated instrument, called a "petrotome." The saw is of the cir- 

 cular type, is made of tin or other soft metal, has no teeth, but has 

 diamond dust driven into the margin. A rigid clamp holds the object, 

 and the saw, constantly cooled by a stream of water, gradually cuts 

 through the specimen. If the piece to be cut is more than 5 or 6 cm. 

 in diameter, a band saw is better; and if the piece is 10 or 20 cm. in 

 diameter, the band saw is necessary. The "saw" is not of the type 



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