2 GYMXOSPERMS 



in solid rock. During the swampy conditions leaves, stems, roots, 

 together with sporangia, spores, and seeds, falling into the swamp, 

 where the water contained calcium or silica, became changed into 

 stone. Starting with a piece of stem or leaf and some sticky clay, the 

 mass would pick up other pieces of stem and leaf, and also spores or 

 seeds, just as one sees the process going on today, until balls as large 

 as one's fist, or even larger than one's head, would be formed. The 

 mass, soaked with lime water, would become calcified, preserving the 

 material so perfectly that not only cell walls but often cell contents 

 can be studied about as in living material. 



To get such material into condition for microscopic study, the 

 time-honored method, and still probably the best method, although 

 very tedious, is to saw through a coal ball, polish a sawed surface, 

 cement this smooth surface to a piece of glass; then saw as close to 

 the glass as possible, thus leaving a thin section firmly cemented to 

 the slide. This thin section is then ground and polished until it is 

 thin enough to be studied with a microscope. It is then cleaned and 

 dried, some balsam and a thin cover glass are added, and the mount 

 is ready for study. 



A later method, much more rapid, and for some purposes almost 

 as good, has come into favor because it is so easy and saves so much 

 time. After sawing through a ball and polishing a surface, the pol- 

 ished surface is immersed in 4 per cent hydrochloric acid for a minute 

 or two; the acid is gently rinsed out with water; the water is removed 

 with 95 per cent and 100 per cent alcohol; the surface is flooded 

 gently with ether alcohol, and then with a rather thick solution of 

 celloidin in ether alcohol. When the ether alcohol evaporates, the 

 celloidin can be peeled off in a thin film, which is placed in equal 

 parts of bergamot oil, cedar oil, and carbolic acid, and then mounted 

 in balsam. Such mounts look much like those prepared by the other 

 slow, laborious process; but all calcareous structures are lost. This 

 method proves that the old theory, that all organic material was 

 changed completely into stone, is incorrect. If it were correct there 

 would be no plant structures in a celloidin peel. 



After taking off a peel, the surface from which the peels are being 

 made is polished for half a minute, then cleaned and dried. It is 

 then ready for another peel. One great advantage of the method is 



