BOTANY 25 



meter with interesting results. It appears that the water 

 present in the soil is not all frozen even when the temperature 

 is lowered to —78° C. It is assumed that this is combined water 

 or water of hydration, and therefore is to be regarded as 

 unavailable to plants. This combined water may amount to as 

 much as 22 percent, in clays, or as little as 0-9 percent, in sands. 

 Of the water which can be frozen, part freezes at 0° C. and part 

 only when the temperature is lowered to — i'5 C. The author 

 therefore classifies the soil water into free water, capillary- 

 adsorbed water, and combined water. The wilting point 

 appears to correspond to the condition where all the free water 

 and perhaps, some of the capillary adsorbed water has been 

 utilised. 



The same writer in a further paper (Feb.) reports results 

 of repeated freezing and thawing, which not only results in more 

 water being ultimately frozen, but also has the effect of raising 

 the temperature at which this occurs. If the conclusion, that 

 the additional water thus frozen is the capillary-adsorbed 

 water, is justified, then, in view of the higher freezing-point, 

 we must assume that, contrary to the current conception, the 

 water film in immediate contact with the soil particles is a 

 weaker solution than that constituted by the free water. 



An extensive paper dealing with the distribution of the 

 South African flora is contributed by Prof. Bews to the Annals 

 of Botany. He divides the vegetation into seven categories, 

 showing increasing favourability for plant life, (i) The driest 

 is represented by the Western Region, with small and irregular 

 summer rainfall, and mostly sandy or stony soil ; Xerophytes 

 and Aristida veld are important features ; (2) Central Karroo, 

 with 3-14 in. of rain increasing from east to west, and more 

 regular than in (i) ; the soil is hard clay, rich in salts, and bears 

 dwarf shrubs and succulents ; (3) S.W. region of winter rains 

 (20-40 in.) and dry hot summers, soils varied, chiefly bearing 

 sclerophyllous shrubs ; (4) sand veld of Kalahari, with 

 10-20 in. of rain, soil mostly sandy, bearing grass or tree veld ; 

 (5) E. thorn veld and succulent shrub ; summer rainfall 

 20-30 in., with clayey soils rich in salts and bearing vegetation 

 similar to (2) ; (6) high veld and Montane areas of E. side 

 with a summer rainfall of 30-50 in., and mist clouds, loose 

 sandy or loamy soils, poor in salts, bearing grass, scrub, and 

 forest ; (7) Eastern Coast belt, with a summer rainfall of from 

 30-40 in., various soils bearing grass, scrub, and sub-tropical 

 forest. 



Despite these different types there are in South Africa a 

 number of widespread species which have close allies, regarded 

 by the author as derived types, which exhibit a discontinuity 

 of distribution that suggests their multiple origin. 



