592 STEVKNSOX— FORMATION OF COAL BEDS. [November 3, 



When one reaches southern Florida, he finds a different type of 

 tidal marsh. Northward, grasses and rushes are the plants which 

 advance the land seaward, hut at the south the mangrove is the 

 agent. That plant abounds on coasts in tropical America and is 

 found northward in Florida to lat. 30°, though it is not abundant 

 above lat. 26°. The eccentric mode of growth exhibited by the 

 special type under consideration, long ago attracted the attention of 

 botanists. Bancroft^"* says that it rises from several strong woody 

 roots which emerge from the ground for two or three yards before 

 tliev unite at the trunk. Tough woody shoots, about three inches in 

 circumference, descend from the trunk to take root and, as the tree 

 increases in size, the shoots increase in number. These by their 

 strength compensate for the looseness of the soil. The tree grows 

 in a low, wet soil by the side of running w'ater. 



The Florida mangrove flourishes only in contact with salt water, 

 being stunted by brackish water. Vaughan'"^' describes it as attain- 

 ing the height of 10 to 20 feet and as grownng in water or so near it 

 that the soil is saturated. The long seeds take root in water not 

 more than one foot deep, leaves being put forth as soon as the sur- 

 face is reached. Besides the tufty roots given off at the base, there 

 are others originating at higher levels from the stem, which grow 

 downwards and embed themselves in the soil. Shaler says that 

 these can descend through 8 feet of water in order to take root. 

 Each becomes a new tree to be multiplied in similar manner. Thus 

 a tree ma\- advance 20 or more feet in a century, the advance being 

 checked only when the water is too deep or the waves prevent root- 

 ing. These growths, as described by Shaler and Vaughan, form 

 dense thickets, a fringe, which is made denser by litter from the 

 trees ; so that debris from the land eventually fills up the space 

 behind and the trees are killed. lUu, in the interval, a new fringe 

 has been formed. In the moist area behind the growth, freshwater 

 types displace the saltwater forms and a swamp results. Shaler 



"" E. Bancroft, "An Essay on the Natural History of Guiana in South 

 America," London, 1779, pp. 76-79- 



105 J -^y Vaughan, " Geologic Work of Mangroves in Southern Florida," 

 Smithsoii. Misc. Coll. Ouart. Issue, Vol. V., 1910, pp. 461-464 



190 



