594, REPORT—1905. 
along the streams and on the open flats, but the winter season is shorter than on 
the High Veld, and tobacco, citrus fruits, mangoes, pineapples and pawpaws, give 
excellent results in sheltered situatiens. Maize, pearl millet, and Kaffir corn are 
grown on the open flats. Sweet potatoes, pea-nuts, and castor beans do well. 
The High Veld is subdivided into moisture belts. The greatest humidity is 
found in a narrow strip on the eastern slope of the Drakensberg, where the rain- 
fall is from 55 to 40 inches, and damp mists occur even in winter. This belt is 
said to be ‘humid all the year round, and is known as the ‘ mist belt’; it pro- 
duces filmy ferns, Hepatice, epiphytic ferns and orchids, and such evergreen trees 
as Podocarpus, Xymatos, and other species characteristic of the forests of the eastern 
districts of Cape Colony. 
Passing either east or west of this ‘ mist belt’ the rainfall rapidly diminishes ; 
it is only 28 inches on the Portuguese frontier, at the Lebombo Range. 
West of the Drakensberg there is a gradual diminution in rainfall passing 
towards the Kalahari Desert. ‘'I'nis produces differences in natural vegetation and 
in crop-producing capacity, but owing to the general uniformity in topography it 
is at present difficult to delimit the belts. 
East of an irregular line drawn somewhere in the neighbourhood of Witbank 
and Heidelberg the rainfall appears to range from 35 to 30 inches. This belt is 
generally spoken of as the ‘ Kastern Transvaal.’ 
From the western edge of this belt to a line drawn somewhere near Potchef- 
stroom, or, roughly speaking, in the Witwatersrand and Pretoria districts, the 
meau rainfall is lower than that of the eastern belt, and probably ranges from 30 to 
25 inches. This may be known as the ‘ Witwatersrand belt.’ 
West of Klerksdorp lies yet another belc, still drier in character, and with a 
markedly different flora; full data are not yet available, but the rainfall will pro- 
bably be found to average from 25 to 15 inches. This belt appears to end at 
about the western border of the Transvaal, where it passes into the Kalahari region 
proper. It is generally spoken of as the ‘South-western Transvaal.’ 
4. Bacteria as Agents in the Oxidation of Amorphous Carbon. 
By Professor M. C. Porrer, M/.A., F.L.S. 
According to present knowledve, amorphous carbon is only available as a source 
of plant food after its union with oxygen in the process of combustion, The author’s 
investigations have proved that under the action of certain bacteria a slow oxida- 
tion of amorphous carbon takes place, CO, is evolved, and the carbon can be at 
once utilised for the nutrition of green plants. This leads to a consideration of 
the possibility that the vast supplies of carbon locked up in the world’s coal-fields 
may be rendered available for plant life without the intervention of direct com- 
bustion. 
Peculiar difficulties were experienced in dealing with the sterilisation of the 
carbon substances employed and the removal of CO,, but after repeated experi- 
ments, and the adoption of special precautions for the elimination of possible 
sources of error, it has been demonstrated that charcoal undergoes slow oxidation 
under the action of a soil bacterium. This has been shown by passing a stream 
of air carefully deprived of all traces of CO, over the charcoal and through a 
Pettenkofer’s tube containing baryta water, the presence of CO, being detected by 
titration against oxalic acid. The control experiments with charcoal under sterile 
conditions showed no eyolution of CO,. Commercial wood-charcoal is seldom 
sufticiently charred. Hence before being employed it was always subjected to a 
temperature of about 1200° in a metallurgical furnace, This treatment served to 
drive away all remaining volatile compounds and render the carbon amorphous ; 
at the same time the entangled oxygen would be mainly converted into CO and 
the calcium salts into the oxide. 
The oxidation has been confirmed by the detection of calcium carbonate in the 
charcoal exposed to the influence of the bacterium, and by the complete absence 
of this salt in the control flasks. A further confirmation is found in the fact that 
