ing in. As the
tiles are laid, enough soil is placed on them to hold them in place
until the ditch is filled.

In laying the tiles an even grade should be maintained (Fig. 86). A
lessening of the grade checks the current of water and tends to cause
a stoppage of the drain.

The water gets into the drain through the joints where the tiles come
together.

The outlet of a tile drain should be protected by brick work or should
be of glazed tile such as the so-called terra-cotta tile, to prevent
injury by frost.

The mouth of the drain should be protected by a screen of wire to
prevent the entrance of rats and other small animals.

GLOSSARY

=Acid=, a chemical name given to many sour substances.

=Albumen=, a nitrogenous organic compound.

=Albuminoid=, a nitrogenous substance resembling albumen.

=Ammonia=, a gas containing nitrogen produced by the decay of organic
matter.

=Annual=, a plant that lives only one year; corn and sunflower are
examples.

=Anther=, the part of a stamen that bears the pollen.

=Available=, that which can be used.

=Bacteria=, very small plants, so small that they cannot be seen
without the aid of a powerful microscope. They are sometimes called
"germs." Some of them are beneficial, some do great harm and some
produce disease.

=Biennial=, a plant that lives two years, usually producing seeds the
second year.

=Bordeaux mixture,= a mixture of copper sulphate, lime and water used
to prevent plant diseases. It was invented in Bordeaux, France.

=Bud=, an undeveloped branch.

=Calyx=, the outermost part of a flower.

=Cambium=, the active growing layer between the bark and the wood of a
tree.

=Capillary=, Hair-like. A name given to very small spaces through
which water flows by the force of capillary attraction.

=Carbohydrate=, an organic substance made of oxygen, hydrogen and
carbon, but containing no nitrogen; cellulose or woody fibre, sugar,
starch are examples.

=Carbon=, a chemical element. Charcoal is nearly pure carbon.

=Carbonic acid gas=, a gas consisting of carbon and oxygen. It is
produced from the lungs of animals, and by the decay or burning of
organic matter.

=Catch crop=, a crop growing during the interval between regular
crops.

=Cereal=, a name given to the grain crops that are used for food.

=Chlorophyl=, the green matter in plants.

=Commercial fertilizers=, materials containing plant food which are
bought and sold in the markets t