A manure containing several ingredients acts in this wise: The effect of all of them in the soil accommodates itself to that one among them which, in comparison to the wants of the plant, is present in the smallest quantity.

And part of the soil is called to wash away
In storms and streams shave close and gnaw the rocks.
Besides, whatever the earth feeds and grows
Is restored to earth. And since she surely is
The womb of all things and their common grave,
Earth must dwindle, you see and take on growth again.

Fertile soil, level plains, easy passage across the mountains, coal, iron, and other metals imbedded in the rocks, and a stimulating climate, all shower their blessings upon man.

I return to the newborn world, and the soft-soil fields,
What their first birthing lifted to the shores
Of light, and trusted to the wayward winds.
First the Earth gave the shimmer of greenery
And grasses to deck the hills; then over the meadows
The flowering fields are bright with the color of springtime,
And for all the trees that shoot into the air.

Many animals even now spring out of the soil,
Coalescing from the rains and the heat of the sun.
Small wonder, then, if more and bigger creatures,
Full-formed, arose from the new young earth and sky.
The breed, for instance, of the dappled birds
Shucked off their eggshells in the springtime, as
Crickets in summer will slip their slight cocoons
All by themselves, and search for food and life.
Earth gave you, then, the first of mortal kinds,
For all the fields were soaked with warmth and moisture.

Plants, in a state of nature, are always warring with one another, contending for the monopoly of the soil,—the stronger ejecting the weaker,—the more vigorous overgrowing and killing the more delicate. Every modification of climate, every disturbance of the soil, every interference with the existing vegetation of an area, favours some species at the expense of others.