1915] CURRENT LITERATURE 419 
salts are presented. For combinations of citric acid and sodium chloride it 
was found that for a wide range of concentrations, mixtures of these substances 
were more toxic than either alone. In this case the effect seems to be additive. 
The concentration of hydrogen ions was found to be the chief factor deter- 
mining the production of giant cells. The production of mucor yeast, which is 
in no wise related to the production of giant cells, is determined chiefly by the 
absence of oxygen in slightly acid media containing sugar.—H. HASSELBRING. 
Food substances and growth.—The fact that any given result in plant 
physiology is usually the result of several factors and is only rarely traceable 
of the causes of soil fertility, and both have been shown to be limiting factors in 
certain cases. Botromty’s work emphasizes the idea that the soluble humus of 
the soil is an essential factor in soil fertility, providing not only food and energy 
for numerous soil bacteria, but also serving as a source of food for plants. His 
interpretation of the work reported in this paper is that the chief interest in it 
centers around the possibility that the nutrition of a plant depends, not only 
upon the supply of mineral food constituents, but also upon a supply of certain 
accessory organic food substances, very small amounts of which are sufficient to 
supply the needs of the plant. He cites literature indicating that other workers 
have found that soil humates stimulate the action of nitrogen-fixing bacteria 
and also that they can be readily assimilated by plants. 
Bottom y finds that when peat is submitted to the action of certain aerobic 
aot organisms (he does not say what ones) at 26° C., it decomposes rapidly ° 
“and a large amount of the humic acid present is converted into soluble 
ammonium humate.” His use of the terms “humic acid” and “humates”’ is 
interesting in the light of the recent statement by SCHREINER® that “the 
compounds . . . . suchashumicacid . . have absolutely no existence, but 
are shown to be mixtures of many widely different compounds. n this 
Sages 3 may be noted that WIELER® has taken the view that “humic 
acids’ g, for example, from the action of bases 
on salts; and that BAUMANN and GUL Ly* y have shown that in peat soils the 
acid properties are due to the colloidal matter of the cell covering the hyaline 
sphagnum cells 
Borromty found that bacterized peat, after sterilization, was an excellent 
medium in which to grow nitrogen-fixing bacteria and apply them to the soil. 
7 Botromty, W. B., The significance of certain food substances for plant growth. 
Ann. Botany 962631450: IQr4. 
*8 SCHREINER, O., The organic constituents of soils. Science N.S. 36:577-587- 
hee 
he, ESeneciwackstum. und Kalkmangel im Boden. 8vo. pp. vii+ 
235- aby avi sey 
AUMANN and GULLY, quoted in Science N.S. 40:492. 1914. 
