Part 3

It is a great pity that we in these colonies burn away so much wood in waste when clearing land, Willie, without thinking of making potash out of the ashes, for it fetches a good price.

Then there is potash in the plant. Has any thing else been found in the ash beside that and carbon?

Yes, my lad. Sulphur or brimstone, lime, soda, flint, ammonia, phosphorus, magnesia, and iron, are contained in trees.

But how could all these things get there?

Why, if we cannot find them in the air to be absorbed by the leaves, they must be in the soil or ground. Now, it so happens that those substances are to be found in different quantities in different places.

How do they get into the plant, father?

Simply by the little rootlets absorbing small particles of them, mixed with moisture.

But do all plants require the same amount of lime, potash, soda, and the others?

No, my dear. There are not two sorts of trees that feed upon the same materials in exactly the same proportions.

Is that the reason, then, why some land is so much better fitted to grow one plant than another?

The reason is, because the one soil has more of the right sort of food in it.

Now I see that if I wanted to grow a good crop of any thing, I must give it plenty of the food it likes best.

Yes, but not too much. For like as too much nice rich food is bad for children, so it is with vegetables: ground may be too rich, as well as too poor.

I have heard people say that it is not wise to grow the same thing in the same soil year after year: why is this?

Because it would gradually consume all the food there, and then it would starve, and look miserable.

Then my beautiful flower-bed will by-and-by cease to bring forth such a fine show as it has done this season.

Of course it will, unless you provide your plants with fresh food.

Fresh food, father; I do not understand you.

I mean, manure must be mixed with the soil.

How is manure food for plants?

Because it contains the materials they require. You throw wood ashes over the ground, and so add sulphur, potash, and carbon. Sea weed manure furnishes plenty of soda. Bone dust contains lime and phosphorus.

It is possible, then, to apply to the ground the amount of solid matter taken out of it by the plant, so that if my radish bed had some manure, it would be as good as it was before my crop came off.

That is perfectly correct, my boy.

But how is it that a gum-tree forest is kept up, for there must be a tremendous lot of lime, soda, flint, and the rest, removed from the soil?

Yes, but when the trees fall, they rot, and the solid parts return to the ground.

Oh, father, the remains are very small, compared to the living tree.

True, because the principal part of a plant consists of the gases, which fly off, and of carbon, which unites with the oxygen of the air.

How does God bring fresh carbon to the forest?