Evening star., 1938-04-28

There may be as many as 25,000,000
invisible plants and animals in a gram
of soil, about the size of fine grain of
sand.
1t would require $4,000 such grains
to make up lump the size of a small
marble
The population of this invisible jungle
is composed chiefly of bacteria. micro
scopic plants Their associates are
moulds, yeasts, algae and protozoa.
Total numbers vary enormously from
time to time and place to place. chiefly
with variations in the food supply.
Such are the estimates of DR.. Charles
Thorn. veteran Department Of Agri-
culture micro biologist, summing up the
present status of scientific knowledge
Of this vast unseen world which forms
an essential link in the chain of life
on earth. BY and large. the life of
the grain of soil is unknown, although
thousands of species have been described.
Although always invisible. DR.. Thorn
says. the activities Of these countless
billions Of organisms under foot can
be measured in various ways For one
thing, carbon dioxide is always escaping
from the surface of the SOIL This comes
from the breathing of the unseen crea-
lures and measurement of the gas may
give rough index of how many are
present. The numbers differ greatly
even from hour to hour.
These organisms are relatively i'm
mune to natural variations in heat or
cold, flood or drought. Even when a bit
of soil has been made absolutely dry
in the laboratory, and then crushed
to powder, the bacteria are still there.
When that bit of soil has been placed
in sterile container of some ferment-
able material there will be seething
mass Of micro o-organisms in few hours.
Sooner or later, DR.. Thorn believes.
this vast, unseen mass of life may be
harnessed to the service of man. At
present only beginnings have been made
in this direction. Some are definitely
helpful to plant life and others un-
doubtedly destructive. One service, with
out which plant life would be unable
to continue very long, is the fiXation
of nitrogen from the air in the soil.
One species of bacterium, the azoto-
bacter, does this in the laboratory and
long has been supposed to be the effec-'
tive agent in nature. Actual examination
of soil samples, DR.. Thorn says, fail to
show more than a few thousands of
these organisms per gram of soil any,
where and often none at all can be
found even in places where it is known
that the nitrogen-fixation process is
going on. Some still unknown form of
microscopic life must be doing the bulk
of the work. Its discovery might be of
very great importance to agriculture.
Another unknown organism is the
agent chiefly responsible for breaking
down the cellulose of dead plants in
the soil. One organism which will do
this is a mould. Aspergillus fumigatus,
which is worldwide in its distribution.
1t is found not only in the soil. but as a
pest on grain, and also in the lungs
of birds. Occasionally 1t is found in
human lungs. 1t breaks down cellulose
readily in the laboratory, but nowhere,
DR.. Thorn maintains, is it found in
sufficient masses to do the titanic job
attributed to it.
The great, invisible jungle, of course,
has to eat. Some demand fresh food
and are responsible for root rot in
plants. The majority find their food
supply in the enormous mass of dead
and dying roots Of annual vegetation.
Few realize how great this is. Recently,
DR.. Thorn says, scientist grew a rye
plant In q pot for four months and
then carefully measured the length Of