LXXXIII 
TINY PLANTS MANUFACTURE FERTILIZER 
I SN'T IT ODD that the tiny plants that can be seen 
only with a microscope, clinging to a clover root, and 
the greatest hydro-electric plant in the world, that at 
Muscle Shoals, are working on exactly the same job, that 
of taking nitrogen out of the air that it may be used as 
fertilizer! 
These plants, or bacteria, grow on the roots of those 
other plants that produce their seeds in pods like beans 
and are known as legumes. 
Nitrogen is one of the most abundant materials in the 
world, yet one of the hardest to use. More than four- 
fifths of the air is nitrogen; so it is everywhere. It is one 
of the most important of plant foods, but it can be used 
only when properly mixed with other materials. And 
nitrogen is very exclusive. It refuses to mix unless cer¬ 
tain conditions are present. 
The fact that the bacteria on the roots of legumes can 
change nitrogen develops many unusual situations. It 
leads to the planting of these legumes on worn-out land 
and, after they have produced their nitrogen compounds, 
to plowing under the crop for the enrichment of the soil. 
Failure to understand these bacteria furnished a 
strange story in the agricultural history of the nation. 
This was in the case of alfalfa, a legume and probably 
the oldest and most productive of all forage crops, which 
was brought by the Greeks from Persia five hundred 
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