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the species in the first column are common enough at consid- 

 erably higher altitudes, which have not been submerged for 

 ages. That some of the species in the second column have 

 not yet had time or opportunity to spread southward or coast- 

 ward as far as the mouth of the river is still less likely. 



6. All streams, the large muddy rivers especially, are subject 

 to seasonal variations in volume. In times of flood every river at 

 every point in its course must either rise (so as to increase the 

 area of its cross-section), or flow faster, or both. But no flood 

 can raise the level of the ocean appreciably; so the mouths of 

 rivers are practically free from seasonal changes of level, and 

 fluctuate only with the wind and tides. And these influences are 

 comparatively slight at Apalachicola, which is protected by a 

 barrier beach a few miles off shore. 



The amount of seasonal fluctuation in any river of course in- 

 creases upstream, to a certain point where the diminishing volume 

 of water (or in some cases the greater slope of the channel) begins 

 to ofTset it. (In the case of the Apalachicola River system the 

 point of maximum fluctuation is far north of the portion under 

 consideration, probably near the fall-line.) As the Florida 

 portion of this river is navigable all the year round, it has not 

 yet been considered necessary to measure its fluctuations, but 

 making a rough estimate I should say that at the point where 

 this excursion terminated the water varies in level about ten 

 feet during the year. 



There are doubtless other environmental factors concerned to 

 some extent in the problem, but those discussed above seem to 

 be most significant, and the last one by far the most important. 

 All the available evidence seems to point to the conclusion that 

 most of the swamp plants confined to the more inland portions of 

 this and similar rivers simply require (or tolerate?) more seasonal 

 fluctuation of water than do those of the estuarine swamps, and 

 vice versa. In the last few years I have observed similar corre- 

 lations between pioneer vegetation and constant water-level 

 in so many other places, both on the coast and in bogs and non- 

 alluvial swamps in the interior, that I am inclined to regard this 

 principle as of universal application, at least in temperate and 



