THE EFFECT OF SLOPE EXPOSURE. 217 



5. Trees of Cussonia spicata appear to have a greater 

 transpiring power on the southern slope than on the northern, 

 i.e., the trees on the northern slope have a greater power of 

 resisting water loss. 



Eventually it is hoped to obtain a more complete idea of the 

 differences on the two sides of the hill by means of whole-day 

 investigations, similar to those described above, at various seasons 

 of the year, and also by continuous weekly observations extending 

 over at least a vear. 



PiEFERENCES. 



^ AiTKEN, R. D. " The Plant Succession in a Type of Midland Tree Veld 

 in Natal," South African Journal of Science, XVIII, pp. 233-243, 

 1922. 



- Bews, J. W. " The Vegetation of Natal," Annals Natal Mus., II, 3, 

 1912. 



^ " An Ecological Survey of the Midlands of Natal, with 



special reference to the Pietermaritzburg district," Ibid., II, 4, 1913. 



* " An Account of the Chief Types of Vegetation in South 



Africa, with Notes on the Plant Succession," Journ. Ecol., IV, 3 and 

 4, 1916. 



^ Harshberger, J. W. " Slope Exposure and the Distribution of Plants in 

 Eastern Pennsylvania," Bull. Geo. Soc. P/iiladeiphia, XVII, 2, 1919. 



* Ramaley. Postelsia, 1901. 



' Forrest Shreve. " Vegetation of the Santa Catalina Mountains," 1913. 



* — — • " The Vegetation of a Desert Mountain Range as conditioned 



by Climatic Factors," Publication 217, Carnegie Institute, Wash., 

 1915. 



9 RoBBiNS. Bull. 224, Agric. Expt. Station, Colorado, 1917. 



