area goes up just about as rapidly as the number series used a few
paragraphs back to illustrate the multiplication of microorganisms.

The surfaces presented in different types of soil similarly affect
plant growth so scientists have carefully calculated the amount of
surface areas of soil materials. Although compost heaps are made of
much larger particles than soil, the relationship between particle
size and surface area is the same. Clearly, when a small difference
in particle size can change the amount of surface area by hundreds
of times, reducing the size of the stuff in the compost pile will:

- expose more material to digestive enzymes;

- greatly accelerate decomposition;

- build much higher temperatures.

_Oxygen supply. _All desirable organisms of decomposition are oxygen
breathers or "aerobes. There must be an adequate movement of air
through the pile to supply their needs. If air supply is choked off,
aerobic microorganisms die off and are replaced by anaerobic
organisms. These do not run by burning carbohydrates, but derive
energy from other kinds of chemical reactions not requiring oxygen.
Anaerobic chemistry is slow and does not generate much heat, so a
pile that suddenly cools off is giving a strong indication that the
core may lack air. The primary waste products of aerobes are water
and carbon dioxide gas--inoffensive substances. When most people
think of putrefaction they are actually picturing decomposition by
anaerobic bacteria. With insufficient oxygen, foul-smelling
materials are created. Instead of humus being formed, black, tarlike