74 PRESIDENTIAL ADDRESS — SECTION C. 



ruug^hly parallel with the Drakensberg ; the change of vegetation 

 f<_)ilovvmg this variation m ranifall neeas to be caretuUy worked 

 Diit in order to correlate it with zones of crop production. For 

 instance, it would be useful to know ))recisely which rainfall 

 average is the lowest safe limit for the production of Maize; 

 we know this in a rough and ready way, but a more precise 

 knowledge might save thousands of i)Ounds to ]jersons intending 

 to take U]) farmin<;' in the neighbourhood of the border line. 



Altitude. — Vegetation may in .some cases be a good guide 

 to altitude as it allects temi)erature and atmospheric moisture, 

 if due allowance is made for the compensating effects of latitude, 

 shelter from cold S.E. winds, etc. Thus the typical Bush-veld 

 vegetation north of Pretoria does not appear to climb above 

 approximately 3.800 feet ; exceptions are found in the case of 

 the sheltered North .slope of the Magaliesberg, and of Aleintjes 

 Kopje, Pretoria, while a few tyj)ically Bu.sh-veld species, such 

 as Chrxsophylliiiii uiagaHs-montannm and Landolpliia capeusis 

 occur at 5,700 feet on Houghton Ridge, Johannesburg, where 

 the flora assttmes a semi-Bush-veld facies. 



Another interesting case is that of the grass Andropogon 

 ccresia-fonnis, which aj^pears to occur plentifully only above 

 (approximately) 5.000 feet, although I have found small patches 

 of it at about 4,900 feet, near Irene, and at Witkoj) on the 

 Vereeniging line. 



Other grasses, such as the larger Tambookie grasses (species 

 of Cymhopogon) are characteristic of the lower Bu.sh-veld at 

 1.500 to 2,000 feet, but whether this is due to climatic conditions 

 associated with altitude, or to lack of adequate means of di.spersal. 

 needs investigation, for the advent of the railway on to the Hi^'h- 

 veld is resulting in the estal)lishment of colonies of at least one 

 species of Lowveld Tambookie at places like Breyten (5.8(So 

 feet), and above Pretoria (about 4.500 feet). 



I merely mention these things in jjassing. as being a]:)parent 

 facts — suggestive of many others — which require more accurate 

 investigation to determine how far our native plants may be 

 used as guides to the character of the .'^oil. moisture, climate (tem- 

 ];erature and rainfall), and altitude, and in connection with these 

 as crop indicators. 



T have even heard old pros])ectors both here and in Califor- 

 nia claim that there are certain i)lants which indicate the occur- 

 rence of the rarer minerals (silver, gold and quicksilver) offer- 

 ing to point them out for a sum of money ; but T have never 

 spent anything on testing tlie theory 



Geographical Distribution. 



The geographical distribution of the component parts of 

 our flora is a fascinating and important subject. More than 

 one botanist has attempted to .sketch the distribution of the flora 

 of South Africa, but the most satisfactorv attemnt was that o\ 

 the late Dr. Bolus in "' Science in South Africa." ))repared for 

 the guidance of the British Association visitors in 1905. 



