496 The Philippine Journal of Science 1914 
a large swamp through which the Casilihan River flows to Lake 
Bay. A number of hot springs are located on the periphery 
of the area. 
In the Tarlac area there are no drainage ditches. The water 
level is persistently higher and the liability to overflow is greater 
than in the Los Banos area. For this reason the abrupt tension 
line surrounding the hot springs swings backward and forward 
through a greater amplitude, coincident with the fluctuations 
in the hot water level. Because of the hot springs the tem- 
perature of the ground water is higher than the general average 
of the region. The continued presence of this warm soil water 
has not been conducive to the development of genetically high 
vegetation. 
THE VEGETATION 
The vegetation of the two areas is very similar, although 
on a much larger scale in the Tarlac area. With a few excep- 
tions the same associations occur in both places, but on account 
of ditches the developmental stages are further advanced in the 
Los Banos area. 
The general appearance of the vegetation does not differ 
greatly between the dry and wet seasons, but many of the 
details show considerable variation. The associations are most 
conspicuously differentiated during the rainy season as active 
vegetation is then at its height. During the dry or hot season 
many of the plants die down to the ground and successions 
between associations of herbaceous species are virtually at a 
standstill. The area is noteworthy for the readiness with which 
a number of strand plants occupy space in a swamp. 
THE BOTTOM THERMAL ASSOCIATION 
In the pools of hot water bacteria and blue-green algae 
( Cyanophyceae ) were found on the bottom and at the surface. 
Collections made by me on December 4, have been examined by 
Dr. W. R. Shaw, who reports on the material as follows: 
A preliminary examination of the material from the hot springs at 
Los Banos presents the following organisms: A very slender filamentous 
plant which appears to belong to Thiotlirix or to some allied genus of 
the sulphur bacteria; a croococcaceous species resembling Aphanocapsa; 
a number of filamentous Cyanophyceae, of which the more abundant appear 
to be an Ampliitlirix, a Hypheothrix, and a Rivularia- like species; and a 
large number of Bacterium- like cylindric cells which are rounded at the 
ends. These Bacterium- like cells may be a gonidial stage of the Rivularia- 
like species, mentioned above. This species consists of long parallel fila- 
ments with thicker middle parts made up of barrel-shaped cells and 
