ALONG THE MANGROVE SHORE 261 



fall on mud too firm to penetrate, they must lie 

 prostrate and seemingly powerless, but not so at 

 all; in a short time roots are emitted from its 

 base. Those from the upper side of the "club" 

 being strongest and directed away from it attach 

 themselves to the mud and begin to pull the little 

 baby tree into an upright position. At the same 

 time the small trunk curves upward, and soon the 

 whole stands as straight as a soldier. 



Mangroves grow in a variety of situations; on 

 land rarely touched by high tide and down to low- 

 tide mark, but not below this, at least in Florida. 

 I have reason to believe that the large, old trees 

 are more sensitive to excessive wet than are the 

 younger, smaller ones. Along the shores of Bis- 

 cayne Bay I have seen large trees at about the 

 limit of low tide but always dead or unhealthy. I 

 take this as an indication that the area which they 

 occupy is subsiding and that it has gone down 

 measurably within the lifetime of these old trees. 

 When young they are fairly rapid growers but 

 when old they add little to their girth each year, 

 and it is difficult to estimate the age of the larger 

 specimens. In the cooler parts of the earth the 

 trees a$d a single annual layer of wood that is 



