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RELATION OF-ALGAE TO DISSOLVED GASES. 175 
They say: “The relation of microérganisms to the oxygen 
content of waters have been investigated, but their rela- 
tion to dissolved carbonic acid has received scant attention, 
probably because of the elusive nature of this gas in water 
and the difficulty of determining its amount. Inasmuch 
as the alge and many of the troublesome protozoa are 
chlorophyll bearing, the relation is one of fundamental 
importance. All such organisms require both oxygen and 
carbonic acid in their metabolic processes. 
“Nitrates are, indeed, important, but inadequacy of this 
explanation became manifest when it was observed that 
some water comparatively low in nitrates, at times sup- 
ported large growths of alge. Another reason for the 
development of the alge in ground water suggests itself, 
namely, the presence of carbonic acid. Its occurrence in 
comparatively large amounts in waters of this class has been 
shown, and there is good reason to believe that the alge 
are influenced by it more than by the nitrates, although 
the latter are necessary. The consumption of carbonic acid 
by diatoms has found illustration in several recent instances 
where Asterionella and Synedra have developed in ground 
waters exposed to the light. In the inlet of a certain reservoir 
where Asterionella was abundant, the water contained five 
to eight parts per million of carbonic acid, while at the outlet 
it was entirely absent.” 
Again, while the overturning brings up nitrogen as free 
ammonia to be oxidized to nitrates when it reaches a supply 
of oxygen, at the same time a supply of CO is carried up 
by the same current which brings up the diatoms them- 
selves. “It is quite possible that the duration of their 
growth is determined by the amount of CO: present, but 
observations on this point are not convincing.” 
In another article Whipple (’94) says: “That diatoms 
need air has already been shown by laboratory experiments; 
but whether it is the Oz or the COz gas of the air has not 
been determined.” 
In an earlier article Calkins (’92) shows that there is 
a maximum of diatoms in April and another in autumn, 
