106 University of California Publications in Zoology. [Vol.8 



It may be claimed that, if the physical and chemical con- 

 ditions in the "red-water" area had not been what they were 

 Gonyaulax would not have occurred in such large numbers and, 

 consequently, the effect of Gonyaulax on the abundance of 

 organisms was, after all, due to physical and chemical causes. 

 However, is it not equally true that the effects of the physical 

 and chemical condition of the water on the abundance of organ- 

 isms were due to biological causesf Obviously, had Gonyaulax 

 not been present, the physical and chemical condition of the 

 water could not have disabled or killed the animals above men- 

 tioned. This tendency so frequently displayed by biologists to 

 resolve biological activities into physical and chemical causes is 

 based on the assumption that an organism is nothing but a 

 physical and chemical ccmiplex. While this may be speculatively 

 true, we should only be practically justified in saying that the 

 effect which Gonyaulax had on the organisms in the vicinity 

 of San Pedro was entirely due to physical and chemical causes, 

 if we had learned to make this animal out of physical mixtures 

 and chemical compounds. 



To adequately estimate the quantity of plankton in a given 

 area of the sea we must consider the influence of biological as 

 well as physical and chemical conditions. In addition to the 

 effects of wind, clouds, fog, rain, snow, ice, light, heat, time of 

 day and season, depth, temperature, salinity, gas-content, and 

 chemical composition of the water, this involves the effects of 

 growth, reproduction, food-relations, and other activities of 

 marine organisms. These factors are more or less correlated, 

 but, as demonstrated by Kofoid (1903), there are variations in 

 the quantity of plankton which are nearly, if not entirely, in- 

 dependent of the particular effects of hydrographic and meteoro- 

 logical conditions. Concerning this Kofoid (1903, p. 503) says: 

 ' ' Somewhat regular alternations of growth and rest, of fission and 

 spore formation, or of parthenogenesis and sexual reproduction, 

 are fundamentally the basis of cyclic movement in [plankton] 

 production. The amplitudes, and to some extent the location 

 and duration of the pulses, are plainly affected by the various 

 factors of the environment .... by light, temperature, vegeta- 



