498 The Philippine Journal of Science 1914 
The rise of the hot water in September, 1914, entirely de- 
stroyed the vegetative parts of these algae. The algae did not 
reappear until the temperature of the hot water near the shore 
had fallen below 52°. 
THE BACOPA-LIPPIA ASSOCIATION 
Bordering the hot water pools and growing along streams and 
on flood plain flats is an association of low succulent plants, 
well characterized by Bacopa monniera (L.) Wettst. 1 This 
species produces a dense carpet of bright green vegetation com- 
pletely covering the ground. Lippia nodiflora (L.) Rich., a 
plant of somewhat similar vegetative characteristics, is often 
present, occasionally in alternation with Bacopa. Whenever 
the association tends to advance into hot water, Bacopa is always 
the pioneer. Often it persistently sends its runners into the 
hot water and they are as persistently killed thereby. 
In the dry season diminution or drying up of the hot water 
pools is not followed by a complete invasion of Bacopa. On the 
contrary it also dries up on account of lack of water, due both 
to the decreased supply and the higher concentration. 
During the dry season of 1913, which was not severe, the 
plants of Bacopa shriveled somewhat and flowered less fre- 
quently than usual, but did not die down to the ground. With 
the first showers of the rainy season, the vegetation reacted 
with vigorous growth, most noticeable in Bacopa and Lippia. 
Each of these species formed extensive mats, soon occupying the 
entire stream beds. Lippia was firmly rooted close to the ground 
at each node, so that when the stream became established many 
plants were submerged, and thus being held under water they 
were drowned. Bacopa grew rapidly upward, forming dense 
mats which gradually sank into the water. The submerged 
parts died, but parts above the water remained alive. Later, 
as the water became hotter, the plants at and below the surface 
were killed. Parts above the water, no longer supported from 
below fell into the hot water and were killed. This rapidly 
pushed the Bacopa back from the hot springs. In one pool 
Bacopa receded more than 2 meters in less than a week. The 
critical temperature is between 48° and 52°, higher than this 
being fatal. The steam, which is constantly rising from the 
pool, is not injurious. It was clearly evident that at tempera- 
tures slightly above the fatal point, if the upper parts of the 
1 The plant indentifications were either made or verified by Mr. E. D. 
Merrill, botanist of the Bureau of Science, Manila, P. I. 
