532 GROWTH 



time and the temperature was not at a maximum, Richards (1929) 

 has suggested that sunhght may have had more effect than temperature 

 on numbers. The kinds of Mastigophora and Infusoria were inversely 

 correlated with the abundance of individuals during the seasonal varia- 

 tions. 



Coe (1932) found Protozoa attached to cement blocks suspended in 

 the Pacific Ocean at La JoUa, from June to October. Protozoan sequences 

 and numbers have been used by Lackey ( 1938a) for the study of sewage 

 pollution of streams. 



Sufficient information is not yet available to explain the sequence of 

 protozoan population growths, or the declines and succession by other 

 species in nature. Many of the factors are interrelated, since the solubility 

 of dissolved gases is a function of temperature, and the oxygen produc- 

 tion of aquatic plants depends on the amount of light. The solution of 

 these ecological problems promises to be of considerable practical value 

 to man, as well as an aid in the elucidation of the growth processes. 



Protozoan Successions: Laboratory 



Cultures maintained in the laboratory are more readily followed than 

 those in natural habitats, and there are many records of the growth of 

 populations of Protozoa, their decline and succession by a compar- 

 able growth of another species. Woodruff (1912) reported that near 

 the surface of mass cultures the sequence was monads, Colpoda, 

 Hypotrichida, Vararuecium, Vorticella, and then Amoeba. The sequence 

 of increase and disappearance was identical with appearance, except that 

 the Amoeba advanced from the sixth to the fifth, and then to the fourth 

 place. A definite succession was not apparent at the center or the bottom 

 of the cultures, and a second cycle was rarely observed. The maximum 

 rise and fall was about equal, but the final disappearance might be long 

 delayed. The differences in the relative potential of division were be- 

 lieved to establish the sequence, which was determined by the food and 

 waste products secreted by the animals. The waste products were shown 

 to be toxic, and the toxicity was species-specific and did not effect other 

 species (Woodruff, 1913b). No relation was found between the titrable 

 acidity and the sequence of the Protozoa (Fine, 1912). The acidity 

 was related, rather, to the activities of the bacteria present. 



Fifteen series of two-liter cultures, made to imitate natural conditions. 



