CLASSIFICATION OF FOSSIL FUNGI 419 



cene era. Other kinds of amber are more recent and may contain 

 the remains of various fungi. 



PREPARATION OF FOSSILS FOR STUDY 



Several methods have been developed for the study of fossilized 

 funo-i. The choice of method, as Seward (1933) has indicated, 

 depends upon the nature of the fossil. Sometimes fossil leaves 

 and fructifications of fungi growing upon them are preserved in 

 carbonized films, especially on the surface of hardened mud. If 

 fragments of these carbonized films can be peeled off, they may 

 be bleached in potassium chlorate and nitric acid, washed in am- 

 monia, and then mounted in Canada balsam for direct examina- 

 tion. If the carbonized film cannot be detached, the specimen 

 is first covered with cellulose acetate dissolved in amyl acetate. 

 After this solution has dried, the specimen is covered with hot 

 Canada balsam and then with melted paraffin, after which it is 

 placed in hydrofluoric acid. This acid dissolves the matrix and 

 leaves the fossil intact. If the paraffin is then removed, the fossil 

 can be examined directly. 



In preparing fossils in coal balls, either thin sections are cut by 

 special machinery, or else sections can be ground down to a suit- 

 able thinness. As an alternative, the smooth, cut surface of the 

 coal ball may be etched by immersion in hydrofluoric acid, where- 

 upon the actual plant substance is left in relief. After the etched 

 surface has been washed and dried, a film of gelatin or of some 

 cellulose ester is poured over it; when this film hardens, it may be 

 peeled off and mounted. This simple method makes it possible to 

 get a score or more of reproductions from the same etched surface. 



CLASSIFICATION OF FOSSIL FUNGI 



It is apparent that fossil fungi cannot be classified on the basis of 

 developmental morphology, as can living species. Their fossil- 

 ized remains must therefore be compared structurally with pres- 

 ent-day forms and, on the basis of evidence which is at best 

 merely fragmentary, must be placed in modern families. When 

 this is done, some appear to resemble living forms closely, and 

 others, as might be expected, do not exhibit such affinities. By 

 use of the generic termination "ites" the resemblance of fossils 



