104 University of California Puhlications in Zoology. [Vol.8 



bacterial activity in the sea, plankton could not exist. If 

 "physical conditions" mean all conditons in the sea affecting the 

 quantity of plankton, then the postulate, while true, is mean- 

 ingless, because it reduces to the statement that if all causes are 

 uniform their effects will be uniform. Again, if the term 

 includes only those conditions in the sea not due to the behavior 

 of organisms, the postulate is not true, for it is apparent that 

 rate of growth, rate of reproduction, and food-relations of 

 marine fauna and flora do influence the quantity of plankton. 

 Furthermore, the term may imply that physical conditions have 

 a more significant effect than other conditions on the quantity 

 of plankton, and that, consequently, we may disregard these 

 other conditions in estimating its abundance. If this is true, the 

 postulate rests on the assumption that the effects of these other 

 conditions are known, for otherwise we could not distinguish 

 more significant from less significant effects. It is, however, 

 difficult to believe that all effects on the quantity of plankton 

 in an area of 133,800 square miles could be discovered from 

 evidence obtained during one haul. Finally the term may imply 

 that, owing to a perfect equilibrium between all conditions 

 affecting the quantity of plankton, knowledge of the effects of 

 some may be regarded as an index to the effects of all. This 

 supposition, however, involves the enormous assumption that 

 such an equilibrium does exist, and this is certainly not justified 

 by the present state of our knowledge. 



Evidently the term "physical conditions" lacks meaning in 

 the sense in which it is used, and consequently the above postu- 

 late collapses. Therefore, all calculations based upon this postu- 

 late necessarily lead to erroneous conclusions. 



Any postulate concerning the abundance of plankton that 

 fails to recognize the influence of organisms on this abundance 

 is inadequate. This is well illustrated by the investigations of 

 Herdman, Scott, and Dakin (1910) who have conducted a very 

 extensive, as well as "intensive study of the marine plankton 

 around the south end of the Isle of ]Mann." After very careful 

 and excellent investigations they conclude (p. 295): "Some 

 organisms show a remarkable regularity in their time of appear- 



