BALANCE BETWEEN LIVING AND DEAD MATTER 543 



in the oceans were w^e to know more about the annual cycle of 

 light in different areas of the oceans and at various depths. These 

 observations could well be carried out aboard weather ships 

 together with measurements on the depth of the thermocline. In 

 this connection, too, I may point out that marine biologists should 

 pay much more attention to the dynamics of the water masses in 

 the oceans, especially to their vertical movements and to their 

 heterogeneous physical and chemical characteristics, as well as to 

 their past "history." 



Interrelationships 



We must next consider other interrelationships. First, let us 

 examine the activity within the phytoplankton cells themselves. 

 When sufficient light is available, they will grow rapidly until the 

 major nutrient constituents in the surrounding water fall below 

 the minimum concentration required for their physiological 

 processes. In any given body of water, the amount of living matter 

 increases while that of phosphorus compounds continuously 

 decreases. Under no conditions does a steady balance obtain, 

 except in its end state, when no more phosphorus is available. 

 Here, then, we do not have a static balance but a dynamic one. 

 But even in this end state, when all the nutrients in the water 

 have been depleted and also those adsorbed as an "internal 

 reserve," one cannot speak of a stable state or an exact balance. 

 The phytoplankton cell itself continues to metabolize, the phos- 

 phorus released is a measure of the decomposition of the living 

 matter when there is insufficient light. During the day, organic 

 substances are rebuilt with the phosphorus lost during the night. 

 Thus, the balance is not static, even w^hen the total number of 

 cells remains constant. Hence, one can speak of an "oscillating 

 balance." The period and the amplitude for this system depends 

 on the length and intensity of the light exposure as well as on 

 individual factors "of activity." 



If w'e now^ turn from a single cell to a pure culture, we may 

 perhaps expect that these oscillations are somewhat stabilized by 

 the different sizes and ages of the cells. This supposition may be 

 carried farther when we have a standing stock of different species 



