Equally important to the plant, however, with the supply of carbonic acid, is the supply of sunshine by whose aid to digest it. The carbon alone is no good to the tree if it can't get something which will separate it from the oxygen, locked in close embrace with it. That thing is sunshine. There is nothing, therefore, for which herbs, trees, and shrubs compete more eagerly than for their fair share of solar energy. In their anxiety for this they jostle one another down most mercilessly, in the native condition, grasses struggling up with their hollow stems above the prone low herbs, shrubs overtopping the grasses in turn, and trees once more killing out the overshadowed undershrubs. One must remember that wherever nature has free play, instead of being controlled by the hand of man, dense forest covers every acre of ground where the soil is deep enough; gorse, whins, and heather, or their equivalents grow wherever the forest fails; and herbs can only hold their own in the rare intervals where these domineering lords of the vegetable creation can find no foothold. Meadows or prairies occur nowhere in nature, except in places where the liability to destructive fires over wide areas together crushes out forest trees, or else where goats, bison, deer, and other large herbivores browse them ceaselessly down in the stage of seedlings. Competition for sunlight is thus even keener perhaps than competition for foodstuffs. Alike on trees, shrubs, and herbs, accordingly the arrangement of the leaves is always exactly calculated so as to allow the largest possible horizontal surface, and the greatest exposure of the blade to the open sunshine. In trees this arrangement can often be very well observed, all the leaves being placed at the extremities of the branches, and forming a great dome-shaped or umbrella-shaped mass, every part of which stands an even chance of catching its fair share of carbonic acid and solar energy.