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1x,c,¢ Gates: Swamp Vegetation in Hot Springs Areas 499 
-plants were supported above the water, those parts could still 
obtain water through the dead stems below. On such stems the 
region just above the water was larger than normal, the same 
as is observed in girdled stems. 
During the moderately severe dry season of 1914, the pool 
nearest Los Bafios dried up completely. The ground was in 
addition well drained by ditches. Even with the coming of the 
rainy season no hot water issued from the vents of this pool, 
until the torrential rains of early September. Then a large 
pool was formed in which the hot water quickly killed Bacopa. 
The stream bed had been occupied by Bacopa and Lippia, but 
when hot water began to flow in it, all vegetation in a channel 
about 30 cm wide was killed. The sharp tension line coincided 
with a temperature of 52°. The hot water spread out into the 
surrounding low areas and killed most of the vegetation. 
Near the hot water vents everything was killed. 
Associated with Bacopa and Lippia is Portulaca oleracea L.— 
also a succulent plant—and, in addition, the ever-present, easy- 
demanding, convolvulaceous Merremia hastata (Desr.) Hallier f. 
In the area immediately around the hot springs, higher ground 
seemed to be the most potent cause for succession. Such spots 
were rapidly taken possession of by Fimbristylis spathacea 
Roth. 
In addition to the immediate vicinity of hot water vents, the 
Bacopa-Lippia association occurs along streams and on low flats 
at or below the water-table level during the rainy season. 
Along streams this association forms a narrow zone extending 
into the water. Landward the association is repeatedly broken 
by clumps of Fimbristylis spathacea Roth, or by other plants. 
Lippia is here much more commonly found, but it seldom sup- 
plants Bacopa. Portulaca occurs in a few such places. There 
are usually no additional species, although two convolvulaceous 
vines, Merremia hastata Hallier f. and Jacquemontia paniculata 
Hallier f., sometimes trail out over the Bacopa. 
On flats, Bacopa spreads out in all directions and forms a 
luxuriant mat of vegetation. A few plants of Lippia may be 
present near the margins, but only rarely in the center of the 
mat. Lippia and convolvulaceous vines are the only species 
associated with Bacopa on the majority of these flats. In case 
the flat is not submerged for any length of time, vines, such as 
Merremia, Jacquemontia, and Cissus trifolia (L.) K. Sch., are 
likely to become more abundant during the dry season. Very 
shortly after the first rains, Fimbristylis spathacea Roth appears 
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