138 



LOWER F.OCEXE Fl.OHAS OF SOUTnEASTEKN NORTH AMERICA. 



strip about 2 miles in widtli is covcrod with 

 mangrrovcs, chiefly Rhizophora and Aviconiiia, 

 iutorspcrsed in th(! somewhat drier areas with 

 extensive tracts of Acrosticluim, some of the 

 fronds of which are 10 feet tall. Bowers of wild 

 figs, fragrant evergreen pitliecolobiums, bam- 

 boos, and ivory palms are also found near the 

 coast. The evergreen forest zone consists 

 chiefly of Sterculiacese, Tiliaceae, Mimosacese, 

 Papihonacese, EuphorbiacciE, Anacardiacese, 

 Melastomace?e, and Rubiac(>a\ with small palms 

 (Chamsedorea, Tritlirinax, and Bactris). 



It may seem improper to say that a flora 

 which contains abundant forms of Artocarpus, 

 Nipa, Cinnamomum, Banksia, and the like is 

 entirely American in character, but from the 

 brief sketches in the botanic discussion it is 

 obvious that these genera, though oriental in 

 the existing flora, were cosmopolitan in the 

 early Tertiary, so that it is misleading to ch-aw 

 conclusions from existing distribution alone. 



The Wilcox waters of the upper embayment 

 were always shallow. There were fringing bars 

 and lagoons as well as deltas, estuaries, and 

 swampy bayous. Most of the Wilcox lignites 

 were probably formed in these coastal swamps, 

 and the immediately underlying clays or clayey 

 sands usually show evidence of roots in place, 

 some of them of large size. The sand films in 

 the lignites indicate flood periods of rivers. 

 The deposits in places show the action of the 

 rivers and the shifting of streams over sand 

 flats. Regarding actual temperatures so little 

 is known of the relations of modem plants to 

 their cUmatic environment that general esti- 

 mates only can be given. 



It is obvious that the flora could not have 

 existed if the region had been ever visited by 

 frost, and temperatures appear to have been 

 like those to-day on the Florida Keys. Aside 

 from the meteorologic evidence that there was 

 a wide coastal belt of abundant precipitation, 

 confirmation is furnished by the flora itself. It 

 woidd seem to me proper to compare the Wil- 

 (u)x flora with those of the regions to which the 

 somewhat loosely used term subtropical rain 

 forest is applied by plant geographers. Too 

 little is known of the Midway ( flora for accu- 

 rate comparisons. If compared with the Up- 

 per Cretaceous flora of the embayment area, in 

 wliich, however, 40 per cent of the genera are 



extinct, the Wilcox would seem to have become 

 more tropical, a progression from what might 

 l)e termed a warm temperate to a subtropicid 

 rain forest. On the other hand, the floras as 

 well as the faunas show a gradual increase of 

 ti'opical conditions in the later Eocene, cul- 

 minating in the Oligocene, the flora of which m 

 southeastern North America is strictly tropical. 



Bailey and Sinnott have fomiidatcd ' a 

 method of approximating climatic factors by 

 a study of the percentage of dicotyledonous 

 leaves with entire and toothed margins. Al- 

 though subject to a variety of modifying fac- 

 tors and as yet practicsdly untested, the 

 method at least offers an additional means of 

 checking results obtained by other methods. 

 The Wilcox flora represented by leaves and 

 leaflets comprises 264 species with entire mar- 

 gins and 46 species with toothed margins, or 

 0.826 per cent of the first and 0.174 per cent 

 of the second. This percentage of entire mar- 

 gined forms is much greater than Bailey and 

 Sinnott find in any existing warm-temperate 

 floras for which they have compiled statistics. 

 It is comparable with the percentage of entire 

 leafed forms in the floras of Ceylon (80 per 

 cent), ManQa (81 per cent). West Central 

 Africa (81 per cent), Queensland (82 per cent). 

 New South Wales (82 per cent), Florida (83 

 per cent). In view of the more complete data 

 obtainable for recent floras and the uncertainty 

 regarding the unknown part of the Wilcox 

 flora positive results are not to be expected. 

 The percentage of entire leaves in the existing 

 floras of moist lowland tropical regions is stated 

 to be 88 per cent. As the Wilcox flora is 

 known to have been one of moist lowlands, it 

 could not on this basis be tropical, which con- 

 clusion is in accord with those derived from 

 other considerations, and I am disposed to 

 consider the close agreement in the percentage 

 of entire-leafed forms between the flora of the 

 Wilcox and that of the existing flora of Florida 

 as being of considerable significance. 



Lianas wcu'e apparently not as common in 

 the Wilcox as they are in the existing floras 

 with wliich it has been compared. No traces 

 of the Bignoniacea;, so common in the Amer- 

 ican Tropics, have been detected, the scandent 



1 Baili'V, I. W., aiKl .Siiinott, E. W., A botajiiial index of Cretaceous 

 and Tertiary climates Seienco, new ser., vol. 41, pp. 832-833, 1915. 



