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perceptible, and some of the species confined to the second column 

 (e. g., Arundinaria, Brunnichia) are more "tropical" than some 

 of those confined to the first (e. g., Alnus, Scirpus, Phragmites). 



2. The proximity of the Gulf of Mexico to the lower portions 

 of the river might affect the climate there by making the summers 

 more humid, or the winters milder, or both. Although this might 

 perhaps be assumed to have something to do with the distribu- 

 tion of Sahal Palmetto or Platanus, it would not explain the 

 abundance coastward of Taxodium, Magnolia, and Alnus, for 

 those are equally at home much farther north and farther inland. 

 Besides the differences due to this cause, like the first, would be 

 very slight. 



3. The water near the mouth of the river is of course a little 

 more salty, and more affected by tides, than that farther up. 

 But none of the plants in the first column are believed to have 

 any particular fondness for salt, with the possible exception of 

 Sabal Palmetto (whose habitat preferences are still a puzzle) 

 and two or three of the herbs; and nearly all of them are common 

 far inland, where there is no tide. 



4. The farther one goes up the river, the higher and firmer 

 the banks become. It may be that Betula, Quercus Michauxii, 

 Acer saccharinum, and a few other trees require a solid footing, 

 but many of the species which are abundant on the soft muck 

 of the estuarine swamps grow just as well or even better on terra 

 firma in the interior. 



5. This region, like many other parts of the coastal plain, 

 is supposed to have been submerged beneath the sea in com- 

 paratively recent times, geologically speaking, and of course the 

 mouth of the river emerged last, which would tend to make the 

 vegetation there more nearly of the pioneer type, if other things 

 were equal. But we know too little as yet of the effects of geo- 

 logical history on vegetation, and besides, the region under 

 consideration is so nearly level that it must have all emerged 

 from beneath the waves almost simultaneously. If the plants 

 along this river were not known anywhere else, then it would be 

 difficult to separate the effects of history from those of some other 

 factors, especially the one next to be described. But nearly all 



