266 



KNOWLEDGE. 



July, 1913. 



thousand metres respectively) with a mountain range above 

 one thousand five hundred metres. The chief rivers cut back 

 deeply into the higher topography, hence, in addition to the 

 main terrace system there is a system of river valleys at a low 

 level, and intervening ridges at a high level, introducing 

 greater complexity into the conditions affecting plant-life. 

 The soils are generally derived from poor shales and sand- 

 stones, but locally enriched by the frequent occurrence of 

 intrusive basic igneous rocks. A table of soil analyses is 

 given. Natal is a region of summer rainfall, and the higher 

 hills are moister than the valleys ; the rain clouds from the 

 Indian Ocean deposit first on the coastal belt, and the rising 

 edge of each successive terrace receives more precipitation 

 than the intervening terrace-plateaux ; mists also contribute 

 largely to the water-supply of the plants. Extensive meteoro- 

 logical tables are given in support of the author's conclusions 

 on the distribution of the vegetation in relation to climatic 

 factors — rainfall and temperature at different periods of the 

 year. There are great variations in illumination, from the 

 low intensity of the bush formation to the full light of the open 

 veld; details are given for various habitats. Interesting 

 details are given as to the influence upon the vegetation of 

 winds, fires, and animals (termites, locusts, caterpillars, earth- 

 worms, mammals) and man ; the effect of termites (" white 

 ants ") on the soil through their tunnelling and nest-building 

 is more than equalled by their direct effect on the vegetation 

 through their fungus-gardening and general scavengering opera- 

 tions. The plant formations and associations are described 

 and illustrated by excellent photographs, with lists of 

 species classified to indicate dominance and biological grouping. 

 The shore vegetation comprises (1) halophilous associations 

 on unstable sand, including Scaevola and Cyperus, 

 Ipomaea Pescaprae, and Mesembryanthemuin associations ; 



(2) psammophilous bush formation on fixed dunes fifteen to 

 seventy metres high, forming a fringing belt along the whole 

 coast of Natal, as much as fifty miles broad in Zululand.and con- 

 sisting of trees with little undergrowth but many lianes; 



(3) lagoon mangrove formation, an interesting outlier of the 

 Eastern mangrove flora with Avicennia officinalis, 

 Rhizophora mucronata, and Bruguiera gymnorhiza, at 

 the river estuaries where the sand-dune bush is interrupted 

 with a Salicornia herbacea association on mud-flats; (4) a 

 Barringtonia association just above the lagoons in wet 

 ground more sandy in nature and not brackish. 



The inland vegetation consists of evergreen dicotylous 

 forest and grassland with summer rains and dry winters ; the 

 lower valleys have a dry climate, low winter temperature, and 

 a xerophytic vegetation. The forest is divided into (1) coastal 

 bush extending up to the edge of the first terrace, about five 

 hundred metres, on south-eastern slopes facing the rain-clouds 

 and sheltered from dry hot winds, with species which mostly 

 extend through tropical East Africa — Albizzia fastigiata and 

 Rhus longifolia dominant; (2) midland bush, also on the 

 south-eastern slopes and receiving the largest rainfall in the 

 region — vegetation in general similar to that of the coastal 

 bush, but with Combretum and Calodendron dominant ; 

 (3) yellow wood bush, forming the larger forest areas of 

 Natal, at one thousand metres and above, with Podocarpus spp. 

 and Olea dominant ; (4) rocky stream flora of the narrower 

 valleys, chiefly differing from the other three types in the 

 undergrowth which includes a rich and varied cryptogamic 

 flora— from its more variable and indefinite character it 

 apparently represents a migratory type in contrast to these 

 three types, which represent the formation on stable topo- 

 graphy ; (5) thorn veld or thorn savannah, including the 

 vegetation of the broader dry valleys, with trees (Acacia spp., 

 and so on) scattered through the veld grassland. 



The veld or grassland (grass savannah), widely distributed 

 in Natal, presents two types: — (1) high veld on the open soils 

 of the higher hills with the larger rainfall, with tall grasses which 

 flower regularly, Anthistiria imbcrbis usually dominant and 

 associated with Andropngon spp., Digitaria, and so on ; 

 (2) low veld on hard dry clays with valley frosts and low 

 rainfall, with more xerophytic grasses (low-growing, more 

 hairy), Anthistiria dominant but tufted and seldom flowering. 

 Associated with the veld grasses are numerous herbs, some of 



which always flower immediately after the burning of the 

 grass ; the majority (including numerous bulbous monocoty- 

 ledons) flower early in the season soon after the first raius and 

 before the grass has grown tall enough to shade them ; and a 

 third class includes taller forms that grow with the grass and 

 flower late. In marshes on wetter parts of the veld the 

 dominant plants are grasses and sedges ; actual lakes are rare, 

 and often contain surprisingly few aquatic phanerogams, and 

 most of the marshes are dried up more or less completely in 

 the dry season. 



CHEMISTRY. 



By C. Ainsworth Mitchell, B.A. (Oxon.), E.I.C. 



THE FUTURE OF MOTOR SPIRIT.— The problem of 

 the future supply of motor spirit is discussed by Professor 

 V. B. Lewes in The Chemical World (1913, II, 111). The 

 trade statistics show that during the last seven years the 

 imports of petrol into Great Britain have risen from eighteen 

 million to eighty million gallons, whereas the increase in the 

 world's output of crude petroleum oil has only been from 28 -5 

 to fifty million tons. Most of the petrol imported into this 

 country has been derived from America and the Dutch East 

 Indies, but the increase in the demand in America has reduced 

 the supply available for export and has raised the price of the 

 crude oil. 



Various methods are now being used to obtain a larger 

 yield of petrol from the crude oil. The gas escaping from the 

 wells in the oil-fields is collected and compressed, and the 

 light spirit thus obtained is mixed with the light fractions of 

 higher boiling-point separated in the distillation of the 

 oil. The specific gravity of the petrol used for motors is now 

 0-720, as compared with 0-680 when a larger supply of the 

 light fractions was available. 



Methods have been devised whereby heavier fractions of 

 crude oils are converted into lighter products, such as, for 

 example, distillation in the presence of a catalytic agent like 

 nickel, or superheating the vapours while in process of 

 distillation. 



In one American process a heavy petroleum fraction, termed 

 " solar oil," is sprayed together with water into an iron retort 

 packed with iron filings and heated to 600° C. The vapours 

 issuing from the retort are fractionally condensed, and yield 

 about thirty-nine per cent, of petrol, thirteen per cent, of 

 solvent spirit, and thirteen per cent, of varnish. 



Professor Lewes points out, however, that crude petroleum 

 oil cannot be regarded as a lasting source of supply, and in 

 his opinion the motor spirit of the future will probably con- 

 sist of alcohol containing about ten per cent, of benzol. 



At the present time about eight million gallons of benzol 

 are recovered in coke-oven plants, while the Scotch shale 

 industry produces each year about six hundred thousand 

 gallons of motor spirit. 



A N EW I RON BACTERI UM.-A bacillus that has a specific 

 action upon solutions containing iron has been isolated by 

 Mr. E. M. Mumford (Chem. Soc. Proc, 1913, XXIX, 79), from 

 the Bridgwater Canal tunnels at Worsley, Lancashire. This 

 bacillus varies in its actions upon iron solution according as 

 to whether it acts in the presence or absence of air. Under 

 aerobic conditions the iron, whatever its condition of 

 oxidation, is precipitated as ferric hydroxide, while under 

 anaerobic conditions no precipitation of dissolved iron takes 

 place, although any ferric hydroxide already precipitated is 

 dehydrated and reduced to bog-ore. It is probable that in 

 nature these two actions take place simultaneously, and 

 account for the deposits of bog-ore found in various places. 



The bacillus is a short organism about two microns in 

 length. It is motile and forms different involution forms. It 

 can be cultivated upon ordinary culture media and grows 

 readily upon potato, on which it forms greenish-brown nodules. 



An enzyme has been separated from the bacillus, and this 

 also has the same specific action upon iron, its optimum 

 temperature of activity being 70° C. Both the bacillus and 

 its enzyme require the presence of nitrogen in the medium in 

 order to act upon the iron salts in solution. 



