PHYSICAL COXDITIOXS. 



137 



(Topper) i\m\ several otlier species of the 

 genus grow on the dunes of Queensland, Vic- 

 toria, and western Australia. 



Littler has been WTittc^n of the plant associa- 

 tions of the AnicTican Tr()i)ics, and collector's 

 notes almost always fail to describe habitats 

 adequately. Tliough the marginal Wilcox 

 lands were low, there was such a large conti- 

 nental area to (lie north from which to draw, 

 and tlie long coast furnished such varied 

 echiphic conditions, that the flora was far 

 richer than floras of small insular areas of the 

 American Tropics of the jiresent, as, for exam- 

 ple, that of the Bahamas, which are relatively 

 close to the mainland and where, in addition 

 to the difficulties of introduction, there is rela- 

 tively great uniformity of echiphic factors antl 

 directly adverse factors exist, such as winds, 

 which limit the floral display. 



Without pursuing the subject in greater de- 

 tail it may be assumed to be proved that the 

 Wilcox flora is a typical coastal flora. When 

 it is compared with recent coastal floras it is 

 at once apparent that its aflinities are entirely 

 with those of tropical and subtropical Ami-r- 

 ica. It has much in common with the Ba- 

 haman flora and that of the Florida Keys but is 

 far richer in arborescent forms. Comparisons 

 with the larger islands of the West Indies show 

 more elements in common, and the differences 

 which are apparent are due to the prevalence 

 of porous coral rock along these recent shores, 

 whereas the Wilcox shores were of a different 

 character. The Wilcox flora agrees most 

 completely with the floras along the Caribbean 

 coast from Central America to northern Brazil. 

 Many genera of the Wilcox flora do not now 

 range through the West Indies, and the expla- 

 nation seems to be that the Wilcox flora more 

 closely resembles the original flora of the whole 

 American equatorial region, which became 

 restricted during the epeirogenetic and cli- 

 matic changes of the Miocene or Pleistocene, 

 and the elements now lacking hi the West 

 Indies never regained all the area of distri- 

 bution which they lost at that time. In a 

 measure confirmatory of this statement it 

 may be mentioned that Ilemsley, in his elal)o- 

 rate discussion of the flora of Mexico and Cen- 

 tral America, lists 698 South American species 

 of flowering plants in tliose floras which iii 

 1888 were unknown in the West Indies. 



These included 1 gymnosperm (Podocarpus), 

 183 monocotyledons, and .514 ihcotyledons. 



The following comments on the existing flora 

 of Tiorthern South America are not out of place 

 in tills connection. Undoubtedly the richest 

 botanic province on the globe is the tropical 

 rain forest of South America. In the monu- 

 mental "Flora Brasiliensis " Martins has de- 

 scribed 22,800 species of plants, and this num- 

 ber ]3robably represents not more than half of 

 the total botanic wealth of tliis trackless wil- 

 derness. W:illacc in 1911 estimated that there 

 were about 80,000 species of flowering plants 

 ill tropical South America; in other words, a 

 number about equal to that of all the other 

 tropical floras of the world combined. This 

 region is also notable in that it comprises the 

 largest equatorial forest of the world. The 

 Amazon plain alone is approximately 2,000,000 

 square miles in area, and it is covered by an 

 almost continuous forest, which extends south- 

 ward along the valleys into central Brazil and 

 along the Atlantic coast to latitude 30° south. 

 It- extends westward to the eastern slopes of the 

 Andes and thence southward into the Temper- 

 ate Zone. It extends northward over the 

 Guianas and tkrough Venezuela to Trinidad, 

 and thence along the coast to Central America 

 and the lowlands along the Atlantic and Pacific 

 coasts of southern Mexico. This wonderful 

 rc-gion may be regarded as a vast preserve in 

 which the living representatives of so many 

 elements of our southern Tertiary floras have 

 not only avoided extinction but become greatly 

 tlifferentiated and multiplied. I have men- 

 tioned the possibility of finding EngcDiardtia 

 ill the western part of tliis relatively unexplored 

 region, and it may contain many other genera 

 wliich were American in past epochs. 



Scemann ' has grapliicaUy described the flora 

 of the Isthmus of Panama, and his description 

 affords an interesting comparison with that of 

 the Wilcox, although it is undoubtedly more 

 tropical and would j^robably be more closely 

 comparable with the flora of the lower Oligocene 

 of om* Gulf States, if that flora was as well 

 known as the Wilcox flora. He says that -the 

 (hines abound in LcguminosiT:!, Euphorbiaceae, 

 coconut palms, and Ilippomano scrub. Cres- 

 ccntia and Paritium form tliiokets. A wet 



I Seemann, Berthold, Flora Panamensis, Botany of the voyage of 

 II. M. S. Herald, pp. 57-340, 1852-1857. 



