HYDROGEN ION CONCENTRATION IN S.A. SOILS. 205 



of close bush or forest type of plant comniuuity also results in a 

 less acid type of soil in the High Veld. 



Suggestions for Future Work. 



The above results are put forward more with the object of 

 making clear the possibilities of the method as applied to South 

 African conditions than for the sake of the information they 

 convey. Once the simple technique of the method is mastered, 

 results are easily obtained. In its application to the general 

 problems of plant ecology the following lines of research suggest 

 themselves. 



1. A comparative study oi the main plant habitats in South 

 Africa. We have chosen two of the main types in Xatal (High 

 Veld and Low Veld) as a starting point. 



2. An application of the method to the study of plant succes- 

 sion, as has been done b.y Salisbury in England.' The reaction 

 at different depths must be studied and definite figures can then 

 be given for the degree of " leaching." 



3. The study of individual plants and their distribution. The 

 soils must be tested in which their roots are actually growing 

 This has an obvious bearing on the important question of " plant 

 indicators." 



4. New light can probably be thrown on many imjjortant 

 economic problems connected with (a) arboriculture, (b) general 

 agriculture, (c) veld grazing and stock diseases. Styvesieckte (stiff 

 sickness), e.g., in cattle, which is becoming somewhat of a 

 menace in certain parts of Natal, appears to be absent from Low 

 Veld soils. Is its degree of prevalence possibly to be correlated 

 with the degree of acidity in the High Veld soils'? 



Much information is already available regarding the degree 

 of acid tolerance in various cultivated crops. A simple method 

 of measuring accurately the degree of acidity in agricultural soils 

 will enable the farmer to select the most suitable crops to grow. 

 Altogether the method appears to be one of the most promising 

 of all those applied to ecological and agricultural problems. 



(5) Any study of the micro flora and fauna of the soil must 

 be correlated with exact determinations of relative acidity or 

 alkalinity. For example, while nitrifying bacteria are active even 

 in acid soils, Azniohacter onh- occurs in neutral or' alkaline 

 soils.*- ^ There is urgent need for investigations on these lines in 

 South Africa. 



6. The colorimetric method of measuring hydrogen ion 

 concentration is not of course to be limited to soils. It can be 

 and has been applied to various animal fluids and a big field is 

 opened up in the possibility of its application to plant juices. 

 Investigations of this nature are also at present in progress under 

 our direction. A single example of the results obtained may be 

 given here. 



In the course of an autecological study of Aloe sapnnaria the 

 cell sap was extracted, after freezing, from eight leaves, the sap 

 from each leaf being kept separate. The oldest leaf, which was 

 somewhat withered and showed signs of approaching death, gave 



