156 
silica. There are comparatively few plants 
that have this power and among the alge 
the forms called diatoms are the only ex- 
amples. They are not found in these hot 
pools. The writer has never heard that 
SCIENCE. 
[N. S. Vou. VI. No. 135. 
silica distributed among the filaments. It 
is a principle well known to the physicist 
that matter in solution is often far more 
likely to be thrown down when foreign 
bodies are in the fluid. The mere presence 
Fie. 
any member of the Cyanophycez has this 
power, and the specimens that he has ex- 
amined from the hot springs gave no evi- 
dence that silicious matter was secreted di- 
rectly around the fibers, for the deposits 
were in the form of granules of amorphous 
of such material offers surface or otherwise 
disturbs the equilibrium and hastens the 
appropriate physical changes. Thus the 
phenomenon of crystallization will take 
place much more quickly and completely 
from a solution if there be strings or other 
