Plants, in fact, compete with one another all round for everything they stand in need of. They compete for their food--carbonic acid. They compete for their energy--their fair share of sunlight. They compete for water, and their foothold in the soil. They compete for the favours of the insects that fertilize their flowers. They compete for the good services of the birds or mammals that disseminate their seeds in proper spots for germination. And how real this competition is we can see in a moment, if we think of the difficulties of human cultivation. There, weeds are always battling manfully with our crops or our flowers for mastery over the field or garden. We are obliged to root up with ceaseless toil these intrusive competitors, if we wish to enjoy the kindly fruits of the earth in due season. When we leave a garden to itself for a few short years, we realize at once what effect the competition of hardy natives has upon our carefully tended and unstable exotics. In a very brief time the dahlias and phloxes and lilies have all disappeared, and in their place the coarse-growing docks and nettles and thistles have raised their heads aloft to monopolize air and space and sunshine. Exactly the same struggle is always taking place in the fields and woods and moors around us, and especially in the spots made over to pure nature. There, the greenwood tree raises its huge umbrella of foliage to the skies, and allows hardly a ray of sunlight to struggle through to the low woodland vegetation of orchid or wintergreen underneath. Where the soil is not deep enough for trees to root securely, bushes and heathers overgrow the ground, and compete with their bell-shaped blossoms for the coveted favour of bees and butterflies. And in open glades, where for some reason or other the forest fails, tall grasses and other aspiring herbs run up apace towards the free air of heaven. Elsewhere, creepers struggle up to the sun over the stems and branches of stronger bushes or trees, which they often choke and starve by monopolizing at last all the available carbon and sunlight. And so throughout; the struggle for life goes on just as ceaselessly and truly among these unconscious combatants as among the lions and tigers of the tropical jungle, or among the human serfs of the overstocked market.