SECTIONAL TRANSACTIONS.—K. 495 
(c) Dr. N. M. Comper.—The Sourness of Soils. 
Sourness is recognised from the agricultural point of view by the charac- 
teristic failure of certain crops, the dominance of certain weeds, the prevalence 
of certain diseases, and a rectification of these conditions immediately following 
the use of lime or chalk. 
The cause of sourness is not the hydrogen-ion concentration, since this is 
sometimes high when sourness, as above defined, is absent. Also it is not 
merely the ratio of calcium to other metals (e.g. potassium and sodium), since 
the addition of neutral calcium salts does not reduce the sourness and the 
addition of potassium and sodium salts does not enhance it. There is, however, 
considerable evidence that the ratio of basic lime to weak bases (chiefly alumina} 
is a fundamental cause of sourness. 
The dominant functions of lime in arable soil appear to be, first, to act as 
a mutual flocculant of the soil colloids and the root hair colloids, and, second, 
to prevent too great an uptake of alumina and other toxic substances. 
(d) Dr. W. H. Pearsatu.—Basic Ratios and Plant Distribution. 
To the plant ecologist the most reliable indication of soil sourness is that 
such soils bear a characteristic heathy type of vegetation. The presence or 
absence of these types of vegetation can apparently be correlated more reliably 
with scarcity of calcium in the soil than with absence of oxygen or high 
hydrogen-ion concentration, although calcium deficiency in uncultivated soils 
is commonly coupled with the two latter factors. E 
The typical heathy plants themselves are remarkable for their very high 
fat content. This necessitates a relatively high basic ratio 7 in the 
nutrient medium, if the absorbing surfaces are to remain unimpaired. The 
alge characteristic of heathy types of vegetation are also found to require water 
in which potassium and sodium salts rather than calcium salts are predominant. 
(e) Prof. J. H. Prisstury.—The Cell Wall and the External 
Medium. 
Evidence is supplied that the cell wall differentiates from a complex plasma 
surface into an inner lamella—namely, cellulose and pectin—and an outer (the 
middle) lamella of pectic and fatty acids. These acids form gelatinous soluble 
salts with Na, K and Mg, but insoluble flocculent salts with Ca. Hansteen- 
Cranner has shown that one result is the disintegration of the differentiated 
tissue behind the root apex when placed in dilute solutions containing only a 
salt of either Na, K, or Mg, owing to the solution of the middle lamella; the 
tissue, on the other hand, remains coherent in the solution of a Ca salt. 
It can be shown experimentally that the relative proportion of these bases 
in the soil materially affects the migration of fatty substances along the walls. 
As a consequence the presence and extent of fat deposition in such layers as 
endodermis and exodermis may be materially modified by the bases in the soil, 
whilst plants forming unusually large quantities of fatty acids, such as the 
plants characteristic of peat habitats, may be disorganised when grown on soils 
containing more Ca as the result of the choking of the tissue immediately behind 
the meristem through the accumulation of insoluble Ca soaps. From this stand- 
point the important ‘basic ratio’ in the soil is the proportion of Na+K+Mg 
to Ca. 
34, Dr. R. C. Kniaur.—The Response of Plants in Soil and Water- 
culture to Aeration of the Roots. 
Maize grown in aerated soii cultures produced a greater weight of dry matter 
than control plants in non-aerated soil. The concentration of CO, in the soil 
atmosphere was markedly higher in the non-aerated series than in the controls. 
Tf normal aeration of the soil was prevented by covering the soil with a seal, 
the concentration of CO, rose as high as 15 per cent. In soil in trial-pots 
without plants the CO, concentration rose as high as 34 per cent. in twenty- 
three days. Maize and white mustard did not respond to aeration in water- 
culture, but aerated water-cultures of wallflower and Chenopodium album showed 
an increase in dry weight over controls. 
1923 ye 
