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%,C,6 Gates: Swamp Vegetation in Hot Springs Areas 497 
heterocysts. They taper toward both ends, and the slender ends are com- 
posed of longer or shorter cylindric cells which are rounded at the tips 
and are of about the same diameter -as the free Bacterium-like cells. 
The bottom forms nearest the hot water vents appeared as 
brownish, gelatinous masses closely covering the bottom. This 
mass was characterized by bacteria. Farther back from the hot 
water vents blue-green algae, growing at the upper surface of 
the gelatinous mass, gave color to the bottom growth. These 
organisms developed in water of a temperature up to 56°. In 
June, 1914, a new vent for the hot water in the center of a 
patch of these organisms resulted in the death of all those plants 
within its sphere of influence until the temperature was lowered 
to 56°. In the pool nearest Los Bafios, during the dry season, 
a layer of bluish-green scum extends quite up to the hot water 
vents. As the water becomes hotter, with the commencing rainy 
season, the plants are killed for some distance from the vents 
until the temperature of the water is lowered to within their 
requirements. Plants were found alive in a few undrained de- 
pressions which existed near the hot water vents. Investigation 
disclosed the fact that these depressions were filled with rela- 
tively cool water, from 44° to 50°, while the water at the sr»- 
face, a few centimeters above, might be from 60° to 80°. Une 
of these pools was stirred up with a stick with the result that 
the temperature at the bottom rose to 65° and on the following 
day all the plants in it were dead. The dead algae and other 
plants in the hot water pools flocculate and form a matrix for 
the deposition of salts found in the hot water. 
With the very high hot water in September, 1914, thermal 
organisms seemed to withstand a higher temperature for about 
amonth. They were very generally found in water with temper- 
atures up to about 60° and in a few extreme cases even up to 
62°. This condition lasted into October, but eventually all of 
these forms that were in water with a temperature above 56° 
succumbed. 
THE SURFACE-THERMAL ASSOCIATION 
Filamentous blue-green algae, some of which are attached to 
the banks of the streams, were very commonly found along the 
streamlets from the hot springs. The critical temperature was 
52°. The mat of these algae helped to support the runners of 
Bacopa which extended from the shore. Upon the establishment 
of the Bacopa association, these algae densely filled the spaces 
and quickly covered any Bacopa stems that sank below the sur- 
face of the water. 
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