TRANSACTIONS OF WAGNER 
VEGETATION OF SOUTH FLORIDA 
80 
Apparently, we have from these figures, the red-mangrove trees growing 
with their roots exposed to fresh water conditions and yet until we reach the 
fork of the Miami River, the trees retain their usual form and usual height. 
How is this to be reconciled with the hydrometric readings of the surface 
water? The explanation seems to be that the salt water, which flows into the 
Miami River from Biscayne Bay, is denser than the fresh water which flows 
from the Everglades. Hence the fresh water flows out on top of the salt water, 
which is beneath. The lower parts of the roots may be influenced by salt 
water, while the upper part of such roots is bathed with fresh. It will be noted 
that the temperature of the river water is colder than either that of the Ever- 
glades, or that of Biscayne Bay. No correction was made in these hydro- 
metric readings for differences in temperature, so that the figures are only 
approximations. At Billy's Creek at 11 A. м. on a bright sunny day, June 4, 
1912, the air temperature of the mangrove thicket was 90° F. (=32° C.), and 
the relative humidity 72%, while in the neighboring salt marsh the air 
temperature was 96° F. (=35° C.) and the humidity 72%, just before a violent 
thunderstorm after which the temperature dropped to 78? F. (=25.6° C.) in 
20 minutes. 
Another fact of considerable interest previously mentioned in a descrip- 
tion of the general distribution of mangrove vegetation is the gradual 
replacement of mangrove trees by the encroachment of the saw-grass 
vegetation of the coastal prairie-everglade and by the saw-grass vegeta- 
tion of river-bank marshes along the Miami River. The shore line of the 
extreme southern end of Florida is fringed by mangrove swamps, and back 
from the Bay of Florida the thicket begins to thin out and as we proceed inland 
the red-mangrove trees become scattered. Between these scattered trees the 
saw-grass vegetation of the coastal prairie-everglade has invaded, and with 
the increase of fresh water conditions, which in itself is not inhibitory, the 
mangrove trees become shorter, smaller, with few branches and leaves that 
begin to assume a light, yellowish-green color. Finally in the competition 
with the saw-grass vegetation, the mangrove is worsted and gradually thins 
out and disappears. This fact is also demonstrated along the Miami River. 
On the river banks the mangrove trees are of the usual size, but back from the 
river in wet depressions controlled by fresh water and saw-grass, the man- 
grove trees become low, sparingly branched bushes, widely arched and ex- 
tended prop roots, yellow-green leaves. This change in vegetation has an 
