for germination. See experiment, page 72.]

[Illustration: FIG. 38.
To show that seeds need air for germination. Corn planted in puddled
clay in tumbler _A_ could not get sufficent air for sprouting. The
moist sand in tumbler _B_ admitted sufficient air for germination.]

=Experiment.=--Fill some tumblers or teacups or tin cans with wet sand
and others with clay that has been wet and then thoroughly stirred
till it is about the consistency of cake batter or fresh mixed mortar.
Take a tumbler of the wet sand and one of the wet clay and plant two
or three kernels of corn in each, pressing the kernels down one-half
or three-quarters of an inch below the surface; cover the seeds and
carefully smooth the surface. In other tumblers plant peas, beans, and
other seeds. Cover the tumblers with saucers, or pieces of glass or
board to keep the soil from drying. Watch them for several days. If
the clay tends to dry and crack, moisten it, fill the cracks and
smooth the surface. The seeds in the sand will sprout but those in the
clay will not (see Fig. 38). Why is this? Water fills the small spaces
between the particles of clay and shuts out the fresh air which is
necessary for the sprouting of the seeds.

This teaches us that when we plant seeds we must so prepare the soil,
and so plant the seeds that they will get enough fresh air to enable
them to sprout, or, in other words, the soil must be well ventilated.

=Experiment.=--Plant seeds of corn and beans in each of two tumblers;
set one out of doors in a cold place and keep the other in a warm
place in the house. The seeds kept in the house will sprout quickly
but those outside in the cold will not sprout at all. This shows us