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THE AMERICAN NATURALIST [Vol. XL VI 



tunately retained their internal structure in condition for 

 successful study, it is probably safe to say that their 

 value to geology as compared with the impressions of 

 plants is as 1,000 to one, and had we only the former, there 

 never could have been developed the science of strati- 

 graphic paleobotany. For example, the collections of the 

 U. S. National Museum embrace over 100,000 specimens 

 of the impressions of Paleozoic plants, whereas of those 

 showing internal structure there is hardly a half dozen 

 unit trays full. In the Mesozoic and Cenozoic collections 

 belonging to the same institution there are thousands 

 upon thousands of specimens from hundreds of localities 

 and horizons, while of those retaining their internal 

 structure there are so few that they can almost be num- 

 bered in tens. 



There is another and an excellent practical reason why 

 the impressions of plants are, and will always remain, of 

 more value to geology than those exhibiting internal 

 structure, no matter how well this structure may be pre- 

 served. As soon as a plant impression is exhumed it is 

 instantly ready for study and may be interrogated at 

 once as to the stratigraphic story it has to tell, whereas 

 the plant with the structure preserved usually shows 

 little or nothing on a superficial examination, and re- 

 quires laborious, expensive preparation before it can be 

 identified. For example — to make a personal applica- 

 tion — for the past five years I have annually studied and 

 reported on from 500 to 700 collections, each of which em- 

 braced from one to hundreds of individuals, and with 

 them have helped the geologists to fix perhaps fifty hori- 

 zons in a dozen states. If it had been necessary to cut 

 sections of these specimens before the geologist could 

 have had his answer, it is safe to say that very little 

 would have been accomplished. 



All fossil plants must be interpreted by and through 

 the living flora. In the more recent geological horizons 

 the plants are naturally found to be most closely related 

 to those now living, but as we proceed backward in time 



