ing plant and animal substances, called "humus."
These enrich the soil, but they do a more important thing: their decay
hastens the release of plant food from the earthy part of the soil, and
they add to it a sticky element which has a wonderful power to attract
and hold the water that soaks into the earth.

_What is the best garden soil?_ A mixture of sand, clay, and humus is
called "loam." If sand predominates, it is a sandy loam--warm, mellow
soil. If clay predominates, we have a clay loam--a heavy, rich, but
cool soil. All gradations between the two extremes are suited to the
needs of crops, from the melons on sandy soil, to celery that prefers
deep, cool soil, and cranberries that demand muck--just old humus.

_How do plant roots feed in soil?_ By means of delicate root hairs which
come into contact with particles of soil around which a film of soil
water clings. This fluid dissolves the food, and the root absorbs the
fluid. Plants can take no food in solid form. Hence it is of the
greatest importance to have the soil pulverized and spongy, able to
absorb and hold the greatest amount of water. The moisture-coated soil
particles must have air-spaces between them. Air is as necessary to the
roots as to the tops of growing plants.

_Why does the farmer plough and harrow and roll the land?_ To pulverize
the soil; to mellow and lighten it; to mix in thoroughly the manure he
has spread on it, and to reach, if he can, the deeper layers that have
plant food which the roots of his crops have not yet touched. Killing
weeds is but a minor business, compared with tillage.

Later, ploughing or cultivating the surface lightly not only destroys
the weeds, but it checks the loss of water by evaporation from the
cracks that form in dry weather. Raking the garden once a day in dry
weather does more good than watering it. The "dust mulch" acts as a cool
sunguard over the roots.

_The process of soil-making._ If the man chopping wood in the Yosemite
Valley looks about him he can see the soil-making forces at work on a
grand scale. The bald, steep front of El Capitan is of the hardest
granite, but it is slowly crumbling, and its fragments are accumulating
at the bottom of the long slope. Rain and snow fill all crevices in the
rocks. Frost is a wonderful force in widening these cracks, for water
expands when it freezes. The loosened rock masses plough their way down
the steep, gathering, as they go, increasing power to tear away any