The Significance of Certain Food Substances for 
Plant Growth. 
BY 
W. B. BOTTOMLEY, M.A. 
Professor of Botany , University of London , King's College. 
With two Figures in the Text. 
E VIDENCE has been rapidly accumulating during recent years which 
proves that the soluble humus of the soil is an essential factor of soil 
fertility, providing not only food and energy for numerous soil bacteria, but 
also serving as a source of food for plants. Amongst numerous investigators 
may be mentioned Krzemieniewski (1), who demonstrated that soil humates 
have a stimulating influence on the fixation of nitrogen by nitrogen-fixing 
bacteria, and Hutchinson and Miller ( 2 ), who have shown that soil humates 
can also be readily assimilated by plants, and serve as a source of 
nitrogen. 
During a search made during the summer of 1912 to find a material 
rich in soluble humates, to serve as a medium for the growth and distribu- 
tion of nitrogen-fixing organisms, it was discovered that when peat is 
submitted to the action of certain aerobic soil organisms at a temperature 
of 26° C., it is rapidly decomposed, and a large amount of the humic acid 
present is converted into soluble ammonium humate. 
This ‘ bacterized’ peat, after being sterilized, was found to be an excellent 
medium in which to grow nitrogen-fixing bacteria and apply them to the 
soil. Mixed with soil in the proportion of 9 oz. of soil to 1 oz. of bacterized 
peat, saturated with a mixed culture of nitrogen-fixing organisms, a large 
increase in the nitrogen content of the soil was obtained after being kept in 
an incubator for seventeen days at a temperature of 26° C., as shown by the 
following tables : 
Plumstead soil. 
Soil plus sterilized bacterized peat (a) 0717 grm. N per 100 grm. soil. 
(b) 0709 
Soil plus active bacterized peat (a) 0792 ,, „ 
(b) 0789 55 55 
An average gain of 77 mg. of N per 100 grm. soil. 
Annals of Botany, Vol. XXVIII. No. CXI. July, 1914.] 
