develop. If there is a tendency for free water to fill the soil a
large part of the time, the farmer can get rid of it by draining the
land. We get here a lesson for the grower of house plants also. It is
that we must be careful that the soil in the pots or boxes in which
our plants are growing is always supplied with film water and not wet
and soggy with free water. Water should not be left standing long in
the saucer under the pot of a growing plant. It is best to water the
pot from the top and let the surplus water drain into the saucer and
then empty it out.

Which soils have the greatest capacity for film water?

=Experiment.=--Place in a tumbler or bottle one-half pound of pebbles
about the size of a pea or bean; pour a few drops of water on them and
shake them; continue adding water and shaking them till every pebble
is covered with a film of water; let any surplus water drain off. Then
weigh again; the difference in the two weights will be approximately
the weight of the film water that the pebbles can carry. Repeat this
with sand and compare the two amounts of water. A striking
illustration can be made by taking two slender bottles and placing in
them amounts of colored water equal to the amounts of film water held
by the pebbles and sand respectively. In the accompanying illustration
(Fig. 29), _A_ represents the amount of water that was found necessary
to cover the pebbles in tumbler _B_ with a film of moisture. _C_ is
the amount that was necessary to cover with a film the particles of
sand in _D_. The finer soil has the greater area for film moisture. It
has been estimated that the particles of a cubic foot of clay loam
have a possible aggregate film surface of three-fourths of an acre.