second, its chemical condition.

"The great needs of the soil are air and water. Just think of all soils
as made up of many particles; let us say like a lot of marbles, one
placed upon another. Each given mass of particles has a given air space
between every particle. Again, if a marble is dipped in water a film of
water remains on it a short time. Let us think of the particles as
always having a film of water on them. Then, as roots and root-hairs of
plants strike down among these they find the two necessities, air and
water.

"Now sand is very loose and so lets the water drain down through it too
rapidly. How shall we improve a sandy soil? Just add something to bind
the loose sand particles together. Humus is good for this binding
purpose.

"Clay absorbs much water. Then its particles squeeze tightly together
and so air is shut out. Add sand to clay soils, to lighten them.

"Humus soil is very rich in nitrogen. This brings us to the chemical
side of soils. There are many chemicals in soils which act as foods to
plants, but only three are the essentials. If these cannot be unlocked
from the soil, or are lacking, they must be supplied. These plant foods
are nitrogen, potash, and phosphorus.

"The chief source of nitrogen is manure; of potash, nitrate or sulphate
of potash, and wood ashes; of phosphorus, bone ash or phosphates. How
can you tell when one of these is lacking? Well, first it is well to
know what each one does for a plant. Nitrogen makes fine, green, sturdy
growth of leaf and stalk; phosphorus helps blossoming plants; while
potash makes plump fruit. If foliage looks sickly then nitrogen is
needed. If one wishes a good growth of leaves, as in lettuce, nitrogen
is needed. If the fruit is small and poor, supply potash; while if the
flower and stalk need better growth, add phosphorus.

"Be careful in adding nitrogen. Nitrogen is the plant food which is most
easily lost out of the soil. Study the soil you are dealing with, supply
if possible what it lacks, and try to unlock to your seedlings the
goodness already in the garden soil."

The interesting talk ended.

"Couldn't we meet oftener than just Saturdays?" questioned Jack.

"We'll see; it all depends upon how much work there is. Possibly we may
have to meet Fridays, too, later on, for you have no lessons that
night. Anything more, boys, before the popcorn?"

"I'd like to know," asked Peter, "if my cousin Philip, who comes from
the city to grandfath