196 BOTANICAL GAZETTE [SEPTEMBER 
and frequently reinforced by other condensations of steam. A 
place of abode of this kind, providing shade, protection, and 
constant moisture in small quantity, would favor the growth of 
such an alga as Schizothrix. 
It is thought that the movement of ihe filaments produced 
in the drop of water on the mounting card is exactly what takes 
place in the drops of water suspended from the ceiling of the 
cave. These not being allowed to evaporate are soon so crowded 
with the rapidly growing filaments that the shape is permanently 
retained. Other drops are added, the alga grows into them, and 
a stalactite is built up. And thus, as it is not difficult to under- 
stand, the process of formation of mineral and algal stalactites 
is quite homologous. 
In attempting to understand what must have been the past 
history of this algal colony, in order to account for the new form 
taken on by the thallus, one meets with a second problem of 
interest, that is, the adaptation of the alga to their peculiar 
environment. Thus, (1) the algal structure is accustomed to a 
state of semi-darkness; even in bright sunlight the entrance of 
more than a small amount of diffused light into the cavity Is 
prevented, and direct light is never possible. (2) It depends 
for its supply of moisture entirely upon that afforded by the 
eruption of the geyser. While the material that forms the cone 
of the geyser is of such nature that moisture can percolate 
through it, the fact that it is higher than the surrounding ground 
would leave it without opportunity for collecting moisture either 
in the form of rain or from underground springs. (3) It accom- 
modates itself to the action of hot water, hot air, steam, and 
cold air. These forces operate at irregular but short intervals of 
time. (4) Accordingly, the growth is neither strictly aerophytic 
nor hydrophytic, but partakes of both characters. 
The temperature of the hot air or steam in the upper part of 
the cavity was found to be 81°C., and this was probably the 
average temperature. Owing to the sudden bursts of steam and 
hot water, it was with much difficulty that a supply of the 
material could be secured. The greater part of this was dried 
