Page:Popular Science Monthly Volume 86.djvu/275

Rh the pipe. The soil water, added to by rain and stream, conserved by cloud and fog, is still further preserved, for the plants which receive it into their roots, by the invisible moisture in the air. For the greater the humidity the less the evaporation from soil and living body, from plant and animal alike. Water is always present, wherever there is a living thing, because, in addition to what is taken into the living body, water is formed in the body and in every cell in which respiration is taking place. The liberation of carbon dioxide in plants and animals is but part of the chemical process which is called respiration. Along with carbon dioxide, water also is formed in the oxidation of the carbon compounds which form the bulk of our food. This is exhaled, or escapes by evaporation, with the carbon dioxide, or is carried off or used. The character of the organism and the nature of the environment determine the amount and the manner of the loss of water by the body.

These are all truths of which we become conscious on reflection, but unless contrasting environments are close together, we are not likely to become conscious of them. In the Rocky Mountains one may see the timbered slopes of one side facing the grassy slopes across the valley. On the Pacific coast, chapparal and forest cover the opposing slopes, meeting at the stream-bed and at the head of the narrow valleys between the ridges of the Coast Ranges. Not the fires of the Indians nor the clearings of the whites account for these contrasts, but rather the relations of the opposing slopes to water, its supply and its loss.

The long valley in which lies the Bay of San Francisco is bounded by ranges of mountains, mainly parallel but strikingly different on the two sides. On the western shore of the Bay, gently rising to the mountain rampart which bars the Pacific Ocean from access, forests and dense shrubby growths, chapparal, cover the still uncleared slopes. The forests are heaviest in the passes, for though the rainfall may be little or no greater there, and the run-off no less rapid, the passes are fog channels. Through these channels the ocean fogs flow, bringing moisture and saving moisture in soil and vegetation. The plants of these east and west passes are strikingly different from those of the cañons which head into the mountain barrier. In the fog channels one sees the foliage and the luxuriant growths of a humid clime: the closed cañons look dry and have drought resisting or short-lived plants except close to the streams, many of which run only for a short time after the rainy season ends. The redwood and the California nutmeg (Torreya californica) may be taken as types of the two localities. The difference is due to water.

In parts of the world where, over great areas, conditions are similar, and the water supply is regularly much above the minimum requirement, the dependence of plants and animals upon water is much less clear, the influence of water upon them much less evident. There can be no