Popular Science Monthly/Volume 86/March 1915/The Physiological Aspects of California for the Botanist
|THE PHYSIOLOGICAL ASPECTS OF CALIFORNIA FOR THE BOTANIST|
IT is almost absurd to speak under one title of a region which forms the Pacific coast of the United States for a distance equal to that from Key West to New York, which extends from sea-level to almost three times the height of Mt. Washington and from the Pacific eastward as far as Utica lies from the Atlantic. But geography and topography merely make, with the assistance of other factors, those complexes which we call climate and soil. There are, therefore, all sorts of climate from sub-tropical to Arctic,—air which ranges from dripping to dry, water which is sweet and water which is brine, growth which is constant the year round or as regularly periodic as winter and summer in the intemperate parts of the "temperate" zone. There are districts in which the daily range in temperature is greater than the seasonal range, soil which bakes to brick and soil which blows in the breeze, and, in places, light which in. amount and in composition is equaled in few other parts of the known world.
If we summarize these statements we shall see that, so far as plants are concerned, it is the condition and the amount of water in air and soil which is the most striking factor in their environment. Water is not only an indispensable food material and the medium in which all the other food materials enter the plant, but it also regulates the kind and the quantity of light which reaches the earth's surface. By so doing it regulates the prevailing temperatures also, possibly to a greater degree than many of us realize.
Water, a simple, stable compound chemically, we seldom think about, taking it for granted when we have it, grumbling when anything interferes with its supply either in quantity or convenience. The average attitude of civilized man to water is similar to his feeling about the daily newspaper. He thinks little or not at all about the labor of mind and body involved in the regular delivery of the daily paper at breakfast time at Ills front door. And if he thinks of water at all, it is only liquid water, of which he demands a supply ample and safe, at his hand by the turn of a faucet. Yet this flowing water is only a small part of what he needs. The water in the pipes is but a small fraction of the total upon which not only his comfort, but also his very life depends. The water in the soil, brought thither as snow or rain, or by stream and possibly by irrigating ditch, is vastly more necessary than the water in 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 greater contrast in appearance, size, texture and behavior, than is offered by the two commonest and most characteristic weeds of the two seasons, the two climates, of this region, namely miner's lettuce (Montia perfoliata) and tar-weed (Hemizonia luzulaefolia).
Miner's lettuce, so named because used in the early gold-mining days of California as a salad, grows in the rainy season, when the temperature is low, often below freezing at night, the humidity high, and the soil wet and soft. Its tender, fleshy, but not thick leaves forming a cup upon a succulent stem which is carried on small and shallow roots, are traversed by slender and simple vascular bundles, and the supporting tissues are slight and weak. Its growth is directly proportional to the available and retainable moisture, for it can hold little water against dry air. In a season of scanty rainfall miner's lettuce is short and small, presenting almost a wizened appearance, and as the dry season comes on it droops, dries and disappears.
Tar-weed, so-called because of the odor of the secretion from the glandular hairs borne on its small dry leaves and the slender woody stem and branches, is a well-rooted summer weed, occupying the grain fields after the crop is harvested or continuing long after the native grasses are dry and dead in the caked soil, growing and blooming till the rains come to soften it and to start its successors. It reaches its best development in dry and solid soil, dry air and daily sunshine. Its consumption of water is probably not less than that of miner's lettuce, but its roots can get water and the rest of its body can hold it, in soil and air so dry that miner's lettuce would shrivel and die. Or, to express a more general truth, water determines the character of the vegetation of the succeeding seasons.
Between the plants of the desert and those growing in the spray of a waterfall one may find all gradations, not only within the limits of the state, but often within the limits of an afternoon's walk. Can one do the like elsewhere on this continent or in Europe?
From a study of these conditions there should come clarity to our conceptions of the relations of water and plants, and ultimately such an extension of our knowledge of these relations as will lead not only to clarity, but to completeness.
Water, as a clear and liquid mass, or very finely divided and greatly diluted by the air, we regard as nearly perfectly transparent, though we know that even the clearest water permits the penetration of light for only comparatively short distances beneath the surface. Cloud and fog, less finely divided water than that which we record as the humidity of the air, are far from translucent. We are beginning, as a result of studies of light in very dry air, to suspect that we have underestimated the influence of water upon the quality and the amount of light available for plants in food-manufacture and acting upon them as a stimulus to other activities. If an effort were made, I have no doubt that a very considerable list might be made of plants known to bloom and to fruit only scantily and rarely elsewhere which fruit regularly under the stimulus of the richer and more abundant light which penetrates the dryer atmosphere of the Pacific coast. Liverworts and mosses, "shade loving" here as elsewhere, fruit abundantly and regularly, but it should be stated that their spores do not always reach perfection because there may not be time enough between the cessation of the rains and the beginning of the really dry season for them to mature fully. But, given the necessary minimum of water in soil and air, plants will fruit, crops will come, the more abundantly the more light of suitable composition they receive. And we shall presently see that the rays of the upper half of the spectrum, the violet and the ultra-violet, the ones most absorbed by water and water vapor, whether visible or not, are the ones most stimulating to bloom and fruit. Soil fertility, light fertility, and water—these three—and the greatest of these is water.