PTIYSTCAL CONDITIONS. 



139 



typos boinp; roprosontod by L^'godium, Aristo- 

 lochia, Mixlpighiiiccu', Cauiualia, Pisonia C*), 

 and Zizyphus. I am inclined lo think Ihat (ho. 

 groat uniformity of clinialic cundilidns, to- 

 gothcr with th(^ ahuiKhint rainfall, liavt^ com- 

 bined to mako the \Yilc()X flora scorn more 

 tropical in cliaractor than was actually the 

 case. That roof ''orals are not found in the 

 Wilcox is I believo entirely due to ])hysical 

 conditions other than those of temperature, as, 

 according to Vaughan,' is so often strikingly 

 shown in Kccent soas. 



I have indicated on the sketch map (fig. 9, 

 C-C', p. loo) what I conceive would bo tho 

 northern limit of range of the Wilcox flora 

 imdor existing climatic conditions in south- 

 eastern North America. 



Most of the generic types of tho Wilcox were 

 probably differentiated by the close of tho 

 Cretaceous period. If, as I believe, the equa- 

 torial region of America was tho place of origin 

 of a majority of those typos which have not as 

 j'et been recorded from tho Cretaceous, thoy 

 must have spread northward along the Missis- 

 sippi Gulf either during the Cretaceous-Eocene 

 interval, during the Midway, or during tho 

 Midway-Wilcox interval. Though the time 

 available for this northward dispersal was thus 

 sufliciently long to account for tlie migration 

 of even the most slowly spreading forms, a 

 short statement on the adaptations and agen- 

 cies of this dispersal is not without interest. 



The Wilcox plants wliich bear winged fruits 

 or seeds are EngeUiardtia, Paraongclhardtia, 

 Dodonsea, Paliurus, Fraxinus, and the Pro- 

 teacen? and MaljiigliiacoiP. None of these 

 plants are capable of long flights except those 

 of tho last two families, which during high 

 winds might readily bo carried for miles along 

 coasts, althougli it is doubtful if they could 

 have crossed great stretches of open water, 

 even through the agency of a West Indian hm-- 

 ricane. The heavier winged fruits, such as 

 those of Engolhardtia, Paraengelliardtia, Pa- 

 liurus, Dodonaea, and Fraxinus, float readily, 

 but I do not know of any experimental data to 

 show how long they can float in oceanic. wat(;rs 

 without losing their vitality. Certainly Do- 

 donaea has reached the Bermudas in recent 

 times tlu-ough tho agency of the Gidf Stream, 

 and Guppy states tliat the fruits of Dodonsea 



1 Carnegie. Inst. Wa-shington Pub. 182, 1914; Washington Acad. Sci. 

 Jour., vol. 4, no. 2, 1914. 



viscoKd float for months in sea water without 

 injury, .\iuong the \\'ilcox forms more or less 

 adapted for lloating, the following genera may 

 ])(■ enumerated: Nipadites, Canna, Taxo(lium, 

 Cara])a,l)alhergia,Canav:dia,Anona,Ciesal})inia, 

 Sopliora, Oirdia, Sapindus, Sterculiocarpus, 

 Trapa, Aviceimia, Solaiutes, ExostcMna, and 

 the Com]>retacea\ Among those forms C'anna, 

 Taxodium, Tra])a, and Exostema are scarcely 

 adapted for s(!a voyagi^s, but, on tho other hand, 

 Nipadites, Sapindus, Storculiocarpus, Aviceii- 

 nia, Carapa, and the Combrctacea; are singularly 

 adapted for dispersal by ocean currents and 

 would be in the van of forms colonizing tho 

 shores of the transgressing Wilcox sea. 



Many of the Wilcox genera had fleshy or 

 ihu|)aceous fruits, wlxich form tho food of mam- 

 mals and also especially of frugivorous birds. 

 Among those forms tli(^ foUowing may he 

 mentioned: Myrica, Ficus, Coccolobis, Mag- 

 nolia, Pisonia, Asimina, Clirysobalanus, Sima- 

 ruba, aU tho Lauracea^ Ilicacea>, Cclastraceae, 

 MjTtaccie, Ebonacea\ Sapotacea;, Meliacese, 

 Euphorbiacese, Anacardiacese, Zizyphus, Guet- 

 tarda, Citharexylon, Cordia, Osmanthus, Ica- 

 coroa, Rhamnus, and Keynosia. Many of these 

 plants bear crustaceous stones that pass unin- 

 jured through birds or are disgorged with their 

 vitidity unimjiaired (avivectent), and these 

 stones could undoubtedly be carried long dis- 

 tances over seas. Even soft seeds, like those 

 of many of the LeguminosiTe, are often ejected 

 uninjured by birds that have eaten them 

 greedily. Birds also may be killed while car- 

 rying undigested seeds. These are by no 

 means unimportant factors in distribution. 

 Clement Roid, in liis discussion of the origin of 

 the British flora, mentions a dead wood pigeon 

 from whose crop beans were sprouting, and 

 when it is remembered what a groat number 

 of birds meet an untimely end it is conceivable 

 that a single hurricane miglit roatiily be the 

 moans of introducing new forms from tlie 

 Antilles on the Wilcox coast. Other Legu- 

 minosiP, although more rarely, are dispersed by 

 ocean currents, for example the modern Entada 

 or snuffbox sealiean. Canavalia ohtusifolia lias 

 buoyant pods and seeds, which retain their 

 vitality after prolonged immersion in sea 

 water, and tins may well have boon true of the 

 Wilcox species of Canavdia that so closely 

 resemble this modern form. 



