RELATION OF ALGAE TO DISSOLVED GASES. 179 
oxygen, an increase producing an intenser red and a smaller 
amount resulting in green. 
This explanation might account for the appearance of red 
Euglena in one of the fish ponds in the state hatchery, a 
little later than the appearance of the bloom on the other 
ponds. Some claim that such forms may change from holo- 
phytic to holozoic and vice versa, in a similar manner, along 
with change of food supply. 
Kofoid (’08) reports the red Euglena as appearing in 
the Illinois River, always associated with Euglena viridis 
and, he thinks, possibly only a variety of the latter; but 
he does not seem to associate it with the variation in oxygen 
content of the water. 
The sudden appearance of a red bloom on Jamaica Pond, 
near Boston, for a succession of summers, is reported by 
Mrs. Ellen H. Richards (’01), but it is not associated with 
any change in the water, except a rise in temperature. It 
consisted largely, if not wholly, of Oscillatoria prolifica. 
The report of Birge and Juday (’11) on the dissolved 
gases of the Wisconsin lakes made its timely appearance 
after some ten or twelve years of mature study. This served 
to shed considerable light on the problem in hand. 
In these studies they find much importance attaching 
not only to the free COz brought by the convection cur- 
rents, but likewise, and more especially, to the half-bound 
COz contained in the bicarbonates of calcium and other 
alkaline earths. In fact these alkaline lakes support the 
richest algal flora and, consequently, the richest fauna. 
Lakes containing a large amount of these substances 
possess, according to them, a source of carbon-dioxide 
lacking in soft-water lakes and can, therefore, support a 
large population of plankton. The reduction of bicarbon- 
ates to mono-carbonates gives an alkaline reaction to the 
upper stratum of the lake. These mono-carbonates must 
take up the carbon-dioxide liberated in the upper water 
by respiration and decomposition, and more will be absorbed 
from the air than is possible if free carbon-dioxide is 
already contained in the water. 
