2(10 REPORT OF NATIONAL MUSEUM, 1892. 



ogical epochs have been necessary to their fossilization, have already 



been referred to, but it is desirable to consider to what extent remains 

 of extinct floras may have been so preserved and fossilized. 



The true aquatic plants or algae, except those belonging to the family 

 Corallinacese, are usually so succulent that they decompose almost as 

 quickly as do the soft parts of animals, and they are therefore repre- 

 sented in sediments only as easts or impressions. Although the diatoms 

 are represented by abundant remains in both marine and nonmarine 

 waters, comparatively little use has been made of them in the systematic 

 study of fossil remains. 



With few and comparatively unimportant exceptions it is only such 

 plants as grow upon marshes which are subject to periodical overflow 

 and sedimentary accretion, and such portions of others as may be cast 

 into adjacent waters by the winds or carried into them by river freshets, 

 that are likely to undergo such sedimentary intombment as would 

 insure their preservation in a condition for satisfactory study. No up- 

 land plants, except portions of those which grow in the neighborhood 

 of bodies of water, are likely to become so intombed, and herbaceous 

 plants, most of which wither and remain attached to their roots, as 

 well as the foliage of evergreen trees, are also not likely to be cast into 

 the water together with autumn leaves of deciduous trees. Again, the 

 fruits of deciduous trees, being usually more compact than their leaves, 

 are not likely to be transported by winds to a sedimentary burial. 



It is therefore apparent that the representation by fossil remains of 

 every formerly existing flora is necessarily very incomplete, not only 

 because of the accidental character of even the most favorable condi- 

 tions for their preservation, but because a large, and apparently the 

 larger, part of every flora existed under conditions which rendered the 

 preservation of any portions of it impossible. Furthermore, the process 

 of intombment, as well as of being detached and conveyed to it, neces- 

 sarily reduced every plant so preserved to a fragmentary condition, 

 and breaking up the rocks in winch they are now found they are una- 

 voidably still further injured and often destroyed by even the most 

 careful collector. 



The incompleteness of representation of extinct animals and plants 

 by fossil remains when they are considered with reference to the entire 

 bodies of living animals and plants has already been referred to. It 

 has also been shown that a large proportion of the animals which lived 

 in the various geological epochs could have left no recognizable trace 

 of their existence because of the perishable nature of all parts of their 

 bodies. From these and other facts which have been stated the conclu- 

 sion is necessary that a very large proportion of those extinct animals 

 and plants which possessed fossilizable parts have never been repre- 

 sented by fossil remains, because those parts, not having fallen under 

 conditions favorable to their preservation, have been as completely 

 decomposed and destroyed as have the soft parts of the same bodies. 



