CO^rPOSITlOX OF THK FLORA. 



Many hotanists love to dwoll on tho tcincrity 

 of tiie palcMjliotanists in dotonniniiig sj^ofios 

 from iiiiprcssions of leaves. I adiuil at tlie 

 outset that Sdiiu^ identilications l)ased on frag- 

 mentary materials are altojietlier too luieertain. 

 Tlici-e is more or less eonverjjenee in foliar 

 cliaraeters in unrelated or I'eniotely related 

 fanulies and tlierc^ may also l)e eonsiderable 

 variation in tlu^ leaves of a sinj^jlc species, but, 

 foliar eliaraeters in general are more fixed than 

 those of almost any oth(>r (ir<;ans of plants. 

 They are subjected to less complex enxiron- 

 mental factors ami always hav(^ i)een. 



It siiould be remendiered that ehai'acters 

 which are less essential to the ^•ital activities 

 of ])iants, such as the form of the leaf, when 

 once acquired may continue practically un- 

 changed for thousands of y(virs and alFoi'd a 

 surer clue to relationship tlian characters more 

 immediately witliin tlie lieUl of action of nat- 

 ural selection. This is sho\\m by tiie persist- 

 ence of fern fronds on the Paleozoic ]:)lerido- 

 spcnns, by the imiformity of eycad-like fronds 

 from the Permian to th(^ Cretaceous, and by the 

 striking persistence of dicotyledonous foliar 

 types from the middle Cretaceous totlie present. 

 This persistence of type in plants is parallel 

 with tlie persistence of superficial and orna- 

 mental shell characters in the Mollusea from 

 the Cretaceous to the Recent, as noted by Dall. 



In the Trojjics, where flowers and fruits are 

 often imobtainal)le or beyond reach, it is easy 

 to learn to recognize most trees by their hal>it 

 ami foliage, but most botanists, systematic or 

 otherwise, give little attention to anything 

 beyond floral structure. 



It is reasonable to conclude that palms and 

 tree ferns are not boreal plants that were in 

 the course of ages restricted to the Tropics, as 

 Xaunuivr once suggested, m an effort to ex- 

 plain tlieir presence within the Arctic Circle on 

 other tiian climatic grounds. Uniformity of 

 cause and effect is the foundation U]ion which 

 rests the whole fal)ric of our knowledge of past 

 events, and it is just as unscientific to assume 

 that the carrying power of water was not con- 

 ditioned by its velocity during the Tertiary 

 period as it is to assume that insolation, hu- 

 midity, rainfall, winds, and all the other factors 

 that constitute the environment of tiu^ vegeta- 

 tion had effects on the flora of ]iast ages dif- 

 ferent in kind from their effects on tlic living 

 flora. 



In a study like this tlie chief empliasis shoidd 

 be l)ased on comparisons with the existing 

 relatives of tiie fossil forms and not on the 

 study of previously descril)ed forms, numy of 

 tlu'ni from remote regions, in the search f(U' 

 s])eci<'s that appear to l)e similar. Correlation 

 with previously described i)aleobotanic forms 

 should not lie neglected, howev(^r, and no de- 

 scri|)tions are complete unless they include a 

 discussion of the res(Mublances and difi'ereiices 

 of fossil forms that show similarities together 

 with their geologic and geographic distribution. 

 E\iMi the most tri\ial characters of the fossil 

 should be car(>fuUy noted, for all these char- 

 acters are valuabli^ in futui-e studies. The 

 living representatives, t heir habitat , range, and 

 variation are of the groatt^st importance in 

 determining what may be called |)aleiiecologv. 



It may be assumed that strand plants and 

 upland ])lants will not be found in association 

 without clear evidence of transportation, aiul 

 if such seems to be the case additional study 

 juay reveal the errors of determination. 



The facts that all floras are dynamic and not 

 static, tiiat all their elements are more or less 

 ]ilastic in their reactions to the infinit ('complex- 

 ity of tlieir en viroiniiei\t . raise some doubt with 

 regard to the melliods and results of ])aleo- 

 ecology, especially as so little is known regard- 

 ing the precise relations between (^xisting plants 

 and their enviroiuuent. At the sanu> time the 

 method used is the only om^ available and it 

 must be considered to ])(^ a legitimate method 

 until negatived in human experience. If it be 

 assumed incorrect, there is no limit to iflle specu- 

 lations as futile as those of medieval times. 



The Wilcox flora as described in the present 

 study comprises considerably nun-e than .300 

 species; the exact number is without signifi- 

 cance, since it is so largely dependent on acci- 

 dents of preservation and discovery and since 

 it is also considerably influenced by the evalu- 

 ation of specific characters. The number 

 might readily be increased to 400 if fragments 

 of ncnv forms were considered the basis for the 

 description of species. 



This fl(H-a is therefore one of the largest 

 floras yet known from a single geologic horizon 

 in a single area, although it is considerahly 

 smaller than the so-called Fort Union floi-a of 

 the Rocky Mountain province, which, how- 

 ever, covers a greater geographic area and a 

 longer interval of time. 



