USEFUL ALGAE — CHASE 411 



The depth at which the compensation point occurs depends on the 

 species as well as on the quantity of light available. The point at 

 which photosynthesis just balanced respiration for certain algae was 

 found to occur from 7 to 20 meters in turbid water and at 30 meters 

 in clearer water. The optimum location for photosynthesis in the 

 lakes of northern Wisconsin was found to be at the surface on cloudy 

 days and at a depth of about 5 meters on fair, bright days. The 

 brown and green algae require liigher light intensities for a photo- 

 synthetic balance than the red algae. The ability of the red algae 

 to live at greater depths than the green or brown algae may be due 

 to the fact that the red algae absorb a greater percentage of blue 

 light. 



Temperature has an important effect on the acceleration or retarda- 

 tion of growth and reproduction, and under exceptional conditions 

 the temperature of the habitat restricts the algal population to certain 

 species. 



The quantity of water or moisture necessary for algal growth 

 varies, as may be seen, from the large amount required by the plants 

 that live submerged in the ocean to the infinitesimal quantity at the 

 disposal of the aerial algae. 



The essential part that algae play in the life cycle of animals, 

 which is their use of carbon dioxide and their throwing off of oxygen 

 in the free state, keeps the water surrounding them pure. A large 

 amount of oxygen is also yielded to the atmosphere during their 

 processes of growth. It is a well-known fact that, whenever land 

 becomes flooded or wherever an extensive surface of either salt or 

 fresh shallow water is exposed to the air, Confervaceae and other 

 allied forms of algae quickly multiply. Stagnant pools and ditches as 

 well as water standing in urns or flowerpots in the open air quickly 

 fill up with green scum and green silken threads. This scum and 

 these threads cannot grow without emitting oxygen, and on a sunny 

 day, the bubbles of oxygen can be observed to collect where the scum 

 or threads are massed together. The oxygen continually passes off 

 into the air while the algae usually vegetate vigorously, one species 

 succeeding another as long as the water remains. When the land or 

 the container dries up, the algal bodies, which are merely membra- 

 nous skins filled with fluid, shrivel and are carried away by the wind 

 or form a papery film over the surface of the soil or the container. 

 The majority of species do not cause the air about them to become 

 obnoxious by their decomposition. Each small individual cell does 

 not yield a great deal of oxygen, it is true, but the aggregate yield 

 from the algal cells is vast when we take into consideration the 

 extensive surfaces of water spread over the earth. Nature has placed 



