392 SOIL PROTOZOA IN SOUTH AFRICA. 



(3) Up to the present the largest number of species of Pro- 

 tozoa from any one soil was twenty-two, obtained from good vine- 

 yard soil under cultivation at Stellenbosch; the smallest number 

 was one, obtained in cultures of soil from under a mango tree in 

 the Durban Botanic Gardens. The geographical distribution of 

 the Protozoa found in South African soils is given. 



(4) Examination of waterlogged soils has shown the presence 

 of trophic Protozoa. The fauna was relatively abundant compared 

 with that of non-waterlogged soils and contained some different 

 genera. Excess of moisture probably causes excystation. 



(5) The relative abundance of any one kind of Protozoon in 

 different soils shows considerable variation. The sequence of 

 appearance of the different groups of Protozoa in water culture is 

 usually Mastigophora, Ciliata and Sarcodina. Ciliata were the 

 most numerous as regards species, Mastigophora and Sarcodina 

 being about the same in number of species. From the point of 

 view of actual numbers of organisms Flagellates are the most 

 numerous. In regard to viability, Ciliates persist longer in a 

 culture than any other class of Protozoa. 



(6) Environmental effects were noted. Room temperature 

 (15°C to 20°C) produced better gr.owths of Protozoa in cultures 

 than did higher temperatures. Darkness seemed to make little differ- 

 ence in the rate of development in cultures. Dark, heavy soils con- 

 taining much humus yielded more kinds of Protozoa than sandy 

 ones, the amount of organic matter apparently being a limiting 

 factor to Protozoa. Samples of soil taken near the surface usually 

 yielded more Protozoa than deep ones. Transvaal and Natal soils 

 collected towards the end of the summer (rainy season) yielded 

 more kinds of Protozoa than those collected in winter. Cultivated 

 soils tended to yield more species of Protozoa than uncultivated 

 soils. 



(7) Cysts of Protozoa are very closely attached to the soil 

 particles. It was experimentally determined that the more finely 

 the soil was pulverised the more protozoal cysts could be detected. 

 As finely tilled soils usually yield heavier crops than less well 

 cultivated ones, it is possible that the finer tillage detaches pro- 

 tozoal cysts, which, if sufficient moisture is present, will develop 

 into trophic forms that may exert either a direct or indirect action 

 on organisms inimical to plant growth. 



(8) So far as our investigations go, relativelv few Bacteria 

 appear to occur in the soils of South Africa, probably due to the 

 dryness and large amount of sunshine causing partial sterilisation. 

 Up to the present the ingestion of Bacteria by Amoebae, Flagel- 

 lates and Ciliates has only been observed on a few occasions. 



Acknowledgments . 



Our thanks are due to manv kind friends for samples of soil 

 for examination, especially to Mr. A. Stead, of Grootfontein School 

 of Agriculture, to Messrs Parish and Williams, of Cedara, and 

 to Mr. T. Hall, of Potchefstroom. 



We also wish to thank the Research Grant Board, for a grant 

 towards the expenses incurred in these investigations. 



