able plant food.

A warm soil.

A ventilated soil.

These are the most important facts about plant growth so far as the
plant grower is concerned. In other words, these conditions which are
necessary for root growth and development are the most important
truths of agriculture, or they are the foundation truths or principles
upon which all agriculture is based. Having found these conditions,
the next most important step is to find out how to bring them about in
the soil, or, if they already exist, how to keep them or to improve
them. This brings us, then, to a study of soils.

[Illustration: FIG. 12.
To show where growth in length of the root takes place. Forty hours
before the photograph was taken the tip of the root was 1/4 inch from
the lowest thread. The glass cover was taken from this in order to get
a good picture of the root.]

[Illustration: FIG. 13.
Radish seeds sprouted on dark cloth. To show root hairs.]

[Illustration: FIG. 14.
To show how water gets into the roots of plants. Water passed up into
the egg through the skin, or membrane, and forced the contents up the
glass tube until it began to overflow.]

[Illustration: FIG. 15.
To show osmose (see page 19).]

CHAPTER III

SOILS

The soil considered agriculturally, is that part of the earth's crust
which is occupied by the roots of plants and from which they absorb
food and moisture.

RELATION OF SOIL TO PLANTS

We have learned that plant roots penetrate the soil to hold the plant
in a firm and stable position, to absorb moisture and with it plant
food. We learned also that for roots to do these things well, the soil
in which they grow must be mellow and firm, and must contain moisture
and plant food, air must circulate in its pores and it must be warm.

How can we bring about these conditions? To answer this question
intelligently it will be necessary for us to study the soil to find
out something about its structure, its composition, its
characteristics; also, how it was made and what forces or agencies
were active in making it. Are these forces acting on the soil at the
present time? Do they have any influence over the conditions which are
favorable or unfavorable to plant growth? If so, can we control them
in their action for the benefit or injury of plants?

We will begin this soil study with an excursion and a few experiments.

Go to the field. Examine the soil in the holes dug for the root
lessons, noticing the differen