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1x,¢,6 Gates: Swamp Vegetation in Hot Springs Areas 501 
THE FIMBRISTYLIS SPATHACEA ASSOCIATION 
Taking advantage of inequalities in the ground in the Bacopa 
association Fimbristylis spathacea Roth commences to develop. 
This species soon builds up small hummocklike clumps in the 
Bacopa. When these clumps are far apart, this association 
appears only in very isolated patches. When near together the 
spreading flower stems of Fimbristylis spathacea form a layer 
or story above the Bacopa, which is growing between the clumps. 
As the plants of Fimbristylis become more numerous the aggre- 
gation of small and large clumps builds up a fibrous turf. This 
turf may sometimes be very dense. When the hot water rises 
in level, it often surrounds the clumps of Fimbristylis which, 
however, do not die unless the hot water entirely covers the 
center of the clump for some time. 
The Fimbristylis spathacea association usually occurs. in the 
immediate vicinity of the hot springs, but may sometimes form 
a narrow belt along streams where the bank is low and very flat. 
Fimbristylis occupies virtually all the area in the association, 
although some Lippia and Bacopa may remain; and vines, such 
as Merremia hastata and Cissus trifolia, as well as invading 
species, may be present. 
Under exceptional conditions where flats of Fimbristylis 
spathacea are burnt over, cogon, Jmperata cylindrica, imme- 
diately follows. Where the Fimbristylis is merely cut or eaten 
off, no cogon follows as the ground is too wet. 
In the Tarlac area this association is not well represented. 
This is due to the pronounced fluctuations in the water level, to 
which Fimbristylis does not quickly adjust itself. At the Los 
Bafios springs the presence of ditches keeps the hot water down 
so that Fimbristylis does not ordinarily become submerged. 
THE DIPLACHNE ASSOCIATION 
The Diplachne association is semiaquatic. The plants are 
rooted below the surface of the water with stems extending above 
the water. This association occurs in warm water at a short 
distance from the hot springs. It is thoroughly dominated by a 
grass, Diplachne fusca Beauv., whose loose lax stems partly trail 
over the water and with partial support become erect. Thus, 
although the plants may be rooted only on the banks, the entire 
centers of streams may be covered with this vegetation. The 
flower stems are about 1 meter high and over them there may be 
trailing vines; such as Merremia, Cissus, and Tournefortia sar- 
mentosa Lam. With these exceptions there are no secondary 
species in the association. 
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