TREES THAT MAKE LAND — STEPHENS 493 



of seedlings were found that had begun to rot and seemed to be dead. 

 There were about a hundred that had recently rooted and had already 

 produced a pair of leaves at the apex, and literally thousands more 

 that had recently fallen and would probably grow if the tides shifted 

 them to a somewhat erect position or carried them away to a less- 

 crowded spot. Some of these fresh seedlings produced rootlets in a 

 week's time after they were placed in upright cans of mud. This was 

 in September, at the end of the main seed-producing season in south 

 Florida. Most seedlings are produced in July and August, although 

 some are produced all year. 



MILLIONS OF YOUNG 



Dr. John H. Davis, of the University of Florida, to whom any 

 writer who discusses mangroves owes a considerable debt, states that 

 an "average vigorous red mangrove tree produces over 300 seedlings 

 during a summer season, and probably over half of these float away 

 from the swamp." Obviously, then, many hundreds of thousands of 

 seedlings — if not millions — are set adrift each year in Florida alone. 



Ocean currents are undoubtedly responsible for the wide distribu- 

 tion of mangroves. The three American species are found on the 

 west coast of Africa (where they probably originated) and, inter- 

 estingly, on both coasts of Central America and in the Galapagos 

 Islands. How they got into the Pacific is a perplexing question. Most 

 botanists doubt that the seedlings migrated around Cape Horn, and 

 fossil records indicate that mangroves evolved after the Panama 

 land bridge rose. In recent years the American red mangrove has also 

 been found in Hawaii, where mangroves are not native but where 

 both Old World and New World species now grow. It has also been 

 reported from Fiji, Tonga, and even from atolls in the Indian Ocean. 



Once the seedling becomes anchored, it grows rapidly, its height 

 increasing as much as 2 feet the first year. During the second year 

 it sends out prop roots, which extend outward from the trunk in suc- 

 cessively widening circles. After 3 or 4 years the tree is braced so 

 securely that it can withstand almost any storm. In addition to the 

 main prop roots, aerial roots may drop from branches, forming sec- 

 ondary trunks with their own prop roots. 



TREES AND CORAL REEFS 



Mangroves are often popularly associated with coral reefs, but while 

 corals and mangroves do in fact exist in close proximity — particularly 

 in Indo-Pacific regions — they thrive best mider quite different condi- 

 tions. Eeef -building corals need clear ocean water which contains 

 little sediment and is m continual motion, while mangroves do best 

 in still, protected, sediment-laden water. Corals require fairly salty 

 water and may be harmed by a drastic change in salinity in either 



