14 EXPLOITATION OF PLANTS 
was replaced by Liebig’s famous mineral plant-food 
theory. Liebig held that plants obtain their carbon 
from the carbonic acid of the air, and their necessary 
ash constituents from inorganic salts in the soil, and 
soil fertility could be maintained solely by the addition 
of mineral fertilisers. 
This was a complete swing of the pendulum; from 
organic food to solely inorganic, We are now learning 
that neither theory was wholly right or wholly wrong. 
There are certain fundamental truths in each of them. 
Just at the period when Liebig’s researches were 
thought to have finally solved the problem of plant 
nutrition, there was arising a new science—bacteriology 
—which was destined to play an important réle in all 
questions relating to soil fertility. Studied at first. 
chiefly in connection with infectious diseases, the new 
knowledge was first applied to plant nutrition problems 
by Schloesing and Muntz in 1877. ~ 
In the old humus days it had been held that “ cor- 
ruption is the mother of vegetation,’ and even Liebig 
taught that nitrogenous organic matter decayed in the 
soil by a chemical process known as “‘ eremacausis,”’ 
with formation of ammonia, which was further con- 
verted into a plant nutrient—nitrate. In 1877 Schloesing 
and Muntz. showed that nitrification was due to the 
action of bacteria, and in 1879 they claimed to have 
isolated the specific organism. This last claim proved 
to be erroneous, for Warrington in 1884 demonstrated 
that nitrification consists of two processes—first the 
production of nitrites, then their conversion into nitrates 
—but it was not until 1899 that Winogradsky succeeded 
in isolating the two kinds of bacteria concerned. 
