666 BOWMAN— ECOLOGY AND 



as indicative of its having come from America, where it is widely 

 distributed, but that in the past it occurred as commonly in Asia as 

 in America, but now only survives in a few places of the Old World 

 Tropics. His reasons for this view are not amplified and it would 

 seem curious that R. conjugata and R. miicronata, which require 

 the same living conditions and have the same methods of dispersal, 

 etc., should have persisted or developed and R. mangle disappeared. 

 The distribution in Florida varies slightly on the east and west 

 coasts. The northern limit is 27° 15' N. Lat. on the east coast, 

 i. e., at Stuart, and Professor Harshberger has noted their scattered 

 occurrence along the St. Lucie River. On the west coast the limit 

 is 28° N. Lat., that is about at Elbow Key and Orange Grove a 

 little north of Tampa, according to the triangulations of Swick,^^*' 

 made recently along the west coast of Florida. On the west coast 

 in the quiet harbors and bays it is slowly encroaching and, according 

 to Professor Harshberger, filling up the estuaries. At White Water 

 Bay, he states, the trees have completely invaded the area so that 

 now there are only small tortuous channels between the mangrove 

 islands. This observation brings before our attention the subject 

 discussed under the next head. 



Geological Considerations. 



In the first place it may be well to state that there are no fossil 

 evidences of mangroves, but this is only to be expected, since the 

 conditions of a mangrove swamp are very favorable to decay on 

 account of the heat and the very large numbers of bacteria of all 

 kinds in the water and swamp-mud. The water here has no pre- 

 servative action on woody tissues as has the water of peat forma- 

 tions and sphagnum bogs, and so debris in the swamp quickly de- 

 composes into mud and soil, not to mention the activity of the hosts 

 of tiny crustacese, mollusca, worms and coelenterates, etc., in the life- 

 filled environment, which all help to disintegrate such organic 

 material. 



The effect of the mangroves themselves on their habitat is very 

 remarkable, as has been mentioned before in this paper and also has 



i^'^ Swick, Clarence H., " Triangulation Along the West Coast of Florida," 

 U. S. Coast and Geodetic Survey, Sp. Pub. No. 16, 1913. 



