214 



THE EFFECT OF SLOPE EXPOSURE. 



Table IV. — Soil Temperatures. 



The difference in the soil temperatures is perhaps more striking 

 than in the case of any other factor, the maximum temperature 

 on the northern slope (26' 4°) being nearly double that on the 

 southern slope (13'50). The minimum temperatures recorded 

 (11-9° and 9'5°), however, only differ by about 2"50, so that the 

 variation in soil temperature is much more extreme on the 

 northern slope than on the southern. Apparently also the heating 

 of the soil on the north side is very uneven, since the differences 

 between the individual thermometers ma}- amoimt to as much as 

 3-60C. 



5. Soil Moisture Content. A sample of the soil was taken at 

 each station and brought into the laboratory, where the water 

 content of a small portion of each sample was determined with the 

 following results : — 



North slope: Water content percentage of fresh wt. = 12-03% 

 South slope: do. =25-43% 



6. Transpiration of Cussonia spicata. This was measured 

 by means of calcium chloride tubes attached to the leaves. The 

 method is one which is being thoroughly investigated at the Natal 

 University College, and will be described in detail later. It does 

 not measure the actual transpiration, but rather the maximum 

 transpiring power of the leaf over a given period. At each stafion 

 three weighed tubes were attached to each tree, each tube being 

 left on the tree for two hours. In the following table the increase' 

 in weight of each tube is given in mgms. : — 



Table V.. — Transpiration. 



