soil protozoa in south africa. 367 



The Succession of Dominant Types. 



In each culture examined, it has been found that for varying 

 periods one species of Protozoon outniunbers the rest, and hence 

 may be termed the dominant type for the time being. If charts 

 are constructed of the number of each kind of organism observed 

 daily in a measured quantity of culture, the succession of 

 dominant types can be determined. This succession varies with 

 the different soils. 



For example, in an examination of soil from the Observatory 

 Garden at Louren^o Marques over a period of 79 days, Euglypha 

 sp. was the dominant organism for the first 47 days, when 

 Peranevia trichopJiorum equalled it in numbers for three -days, 

 and after three days more became dominant. After yet another 

 three days, the number of Peranema had fallen greatly, and the 

 Euglypha reassumed dominance. On the 62nd day. Amoeba 

 prate us suddenly became dominant and retained its dominance 

 for four days, after which time A})ioeba protciis and Peranema 

 iricliophorum were dominants alternately. 



Secondar}^ or sub-domin;mts M^ere also noted. Thus, at a 

 period when Euglypha sp. was markedly dominant, Amoeba 

 proteus and Peranema iricJwphorum were almost equal in 

 numbers and their graphs were parallel. They definitely were 

 subdominant to the Euglypha. Later, when Peranema iricho- 

 phorum was dominant. Amoeba proteus became subdominant, and 

 when Amoeba proteus in turn became dominant, Cyclidium 

 glaucoma became its subdominant. 



The succession of dominants in cultures of Liesbeek 14 soil 

 is interesting. For the first ten days, Euglypha sp. was the 

 most abundant organism and was dominant. Then Euglena 

 oxyuris suddenly assumed dominance and retained it for twelve 

 days. Acthioptirys sol next became dominant, but for two days 

 only, when Euglena oxyuris regained numerical supremacj^ for 

 five days. The flagellate was then replaced as dominant in 

 numbers for one day by Amoeba proteus, then regained its posi- 

 tion as dominant for five days, when Actinophrys sol attained 

 equal numbers. This, however, was not maintained, and Euglena 

 oxyuris again became the dominant organism in the culture and 

 remained so for twenty-eight days. 



Euglypha sp. was the most marked subdominant in this 

 culture. Amoeba proteus being far less numerous. 



In the two cases investigated, namely, in soils from Lourengo 

 Marques Observatory Garden and Liesbeek 14, the sequence of 

 group dominants in each appears roughly to be Thecamcebae, 

 Flagellata. and Ehizopoda. 



Sporadic Appearances of Protozoa in Cultures. 



As mentioned in our previous paper, sometimes a Protozoon 

 appears in a culture on a certain day and then disappears for a 

 considerable period. Usvially such organisms are few in number, 

 frequently only occiu'ring singW in the specimen examined at any 

 one time. 



