202 FLORIDA GEOLOGICAL SURVEY I3TH ANNUAL REPORT 



But saw-grass being evergreen, the foliage present at any one time 

 represents more than one year's growth, so that the proper proced- 

 ure would be to first mow down a small patch of it in midwinter, 

 and then cut and weigh a measured area from the same patch a year 

 later. 



Peat prairies. These are basins reaching a few to several feet 

 below the ground-water level which have become filled with peat, 

 and are covered with herbaceous vegetation other than saw-grass, 

 presumably on account of the water being purer or at least less 

 calcareous than in the saw-grass marshes. They are more com- 

 mon in the lake region than elsewhere. In the course of develop- 

 ment from lake to peat prairie the vegetation has of course under- 

 gone considerable change, beginning with none at all and passing 

 through the aquatic and marginal types above mentioned. That 

 growing on the surface of the peat at present is much like that of 

 some of the lake margin prairies described on the next page, ex- 

 cept for the frequent occurrence of dense clumps of bay {Magnolia 

 glauca) and other broad-leaved evergreens, a few rods in diam- 

 eter. The most characteristic plants have been listed in the Third 

 Annual Report (pp. 274-275), and do not need to be repeated here. 

 The herbs are mostly grasses and other monocotyledons. The peat 

 in such places is among the purest to be found anywhere. 



Basin prairies (fig. 16). The flat-bottomed lakes which drain 

 off at intervals through subterranean outlets, in the Hernando ham- 

 mock belt and farther north, are carpeted when dry with herbaceous 

 vegetation that has not been carefully studied, but consists largely 

 of plants whose indigeneity is under suspicion, for they grow also 

 in places that have obviously been altered artificially. The most 

 characteristic seem to be dog-fennel, Eiipatorinni capillifolium, and 

 a grass, Anastrophus paspaloides, as stated in the Third Annual Re- 

 port, page 261. The weediness of the vegetation is doubtless largely 

 due to the fact that such areas have long been closely grazed by 

 cattle and sheep. 



Lake margin prairies (fig. 26). Some of the larger lakes that 

 are so shallow that a small change in water level makes a great 

 difference in the position of the shore line have the area between 

 high and low water covered with grassy vegetation similar in aspect 

 to that just mentioned, and containing some of the same plants and 



