xkld-iurninc. kx im-.rl mf.nts at c.rokn kloof, prktoria. 293 



Summary. 



1. The burning of the veld and denudini^ the soil of its 

 protective vegetation tends to encourage the flowering of many 

 plants, particularly hemicryptophytes, by allowing the access of 

 light and warmth. In the development of the succession on the 

 burnt portion there appears to be a definite life history, and the' 

 formation of vernal aspect societies. Anthistiria imherhis at 

 tirst is the dominant grass, but there is an invasion later of 

 Trachypogon polymorphns and Andropogon spp., and on portions 

 left unburnt for several years the latter species tend to replace the 

 A n thistiria imherhis. 



2. On bare soil the temperature during the day is considerably 

 higher than on soil covered with vegetation, and tbe same at 

 night ; but, taking the daily maximum and minimum tempera- 

 tures, then soil protected by a covering of vegetation has a more 

 even temperature, and does not exhibit such extremes of heat 

 and cold. 



3. Soil denuded of its vegetation absorbs more water after 

 rain than does soil covered with vegetation, but also loses it more 

 quickly by evaporation ; whereas soil with a protective covering 

 of vegetation, while not absorbing the same amount of water 

 after a rainfall, loses its water more slowly, and consequently 

 does not fluctuate between a very high and very low moisture 

 content, but is more stable in this respect. 



The few observations made during the latter part of last 

 year at Groenkloof are the beginning of a series of experiments 

 being carried out there by the Division of Botany. I realize 

 that at tkis stage it is too early to draw any but very general 

 conclusions ; but this note has been published only with the 

 intention of placing on record the observations made up to the 

 present. 



Data relating to the mechanical and chemical examination of 

 soils from plots A, £>, and C. as determined by Dr. C. F. Juritz, 

 are appended. 



Copy. 



Agric. Chemical Research Laboratory, 



Department of Agriculture, 



Cape Town, isth April. 1919, 

 The Chief, Division of Botany, 

 Pretoria. 

 I subjoin particulars in regard to the mechanical and chemical 

 examination of the three samples of virgin grass-veld soil, A.. B. and C-.. 

 from the Drylands at Groenkloof, near Pretoria, sent under cover of 

 your minute No. P. 115/18 of the 26th September last- 



The ground, I understand from your minute, slopes very gently 

 down to the Groenkloof Valley, and at the lower end of the area — about 

 100 yards square — whence the samples were taken, the soil is red in 

 colour and almost level. It was from this lower end of the ^rea, I 

 gather, that sample C. was taken, while A. and B. were taken from its 

 trpper end, where the ground is very stony and of a light yellow colour. 

 The samples were described as follows : — 



