RELATION OF ALGAE TO DISSOLVED GASES. 203 
APPARATUS AND MATERIALS. 
In all experiments in which measured amounts of gases 
were employed, or definite pressures of gases were desired, a 
Bunsen suction pump with manometer was used, and gas 
generators were attached in the manner described by Wes- 
brook (05), or somewhat similar to that described and used 
by Chapin (’02) in his studies on the influence of COz on 
plant growth. 
The method of collecting and determining the amounts of 
oxygen in water was that described and used by Whipple and 
Parker (’02) in their studies. The method is commonly 
known as Winkler’s method. It is more fully described by 
Birge and Juday (’11). 
Another method, based upon the reducing power of ferrous 
sulphate, was also used as a check and as an alternative, many 
determinations being made by both methods. 
Samples were usually taken and determined in duplicates, 
and, in case of doubt, were many times repeated. The 
purest of chemicals obtainable were used throughout. 
SUMMARY. 
1. There is an intimate and mutual relation between the 
algee and submerged aquatics in a body of water and the gases 
dissolved in that water. They fluctuate together. 
2. Air, or its constituents, oxygen and COz, are as essential 
to water plants as water is to land plants, and equally difficult 
to secure. 
Warm and stagnant water is poorer in these essentials than 
colder water gently agitated by wind or currents. 
4. Currents are especially beneficial to attached plants by 
renewing or removing these gases. 
5. Some species demand more aération than others. 
Some species are more tolerant of stagnant waters than 
others. 
6. Filamentous forms with large cells and thin outer walls 
are best adapted to stagnant waters. Such forms predominate 
in warm, tropical fresh waters, which are poorly aérated. 
The photosynthesis of rapidly-growing alge and aquatic 
