180 ; MISSOURI BOTANICAL GARDEN, 
Angelstein (10), working with a number of different 
kinds of water plants, found that photosynthesis, as shown 
by the bubble method, was proportional to the concentra- 
tion of bicarbonates present in the water and that in dis- 
tilled water, free from carbonates, but saturated with free 
COz, the photosynthesis was very slight. Water saturated 
with air alone gave very slight activity, as shown by the 
bubbles, but was greatly increased by the addition of a small 
amount of KHCOs, or NaHCOs. The maximum was 
reached at about 1% to 1.5% solutions, and above that 
decreased on account of too high osmotic pressure. Solu- 
tions of like osmotic pressure gave like results. Concen- 
trated solutions of calcium bicarbonate always gave a higher 
oxygen excretion than tap water saturated with free COz. 
In natural waters an equilibrium is established between the 
COz pressure of the carbonates in the water and the CO2 
pressure of the air. 
An abundance of dissolved carbonates, according to Birge 
and Juday (’11), increases the supply of carbon-dioxide 
for plant use, both directly and indirectly; directly, by 
the original stock of half-bound COz in the bicarbonates; 
indirectly, because the mono-carbonates take up more CO2 
from the air than would be absorbed without their aid, 
and also absorb that liberated in the upper water by 
respiration and decay. Much of this last would escape into 
the air, especially at night, if not so absorbed. 
Morren (’41) confined a part of the water in an aquarium 
with its contained organisms, under a large balloon flask 
during the night. Analysis in the morning showed the gases 
present in a very different proportion from that found in 
the free water, twice as much COs in the flask, showing that 
there must be a great loss of COz from the free water during 
the night and presumably a like amount of oxygen during 
the day. 
In such hard-water lakes as those above described, Birge 
and Juday (11), find the epilimnion to be permanently 
alkaline during the summer, which shows that more CO2 
is withdrawn from the bicarbonates than is supplied to 
