The extract is representative of all chapters of this outstanding work by the author/biologist. The importance of water and of rain to the continued well-being of the natural ecosystems is an underlying item of knowledged that few students of life research first-hand.

The huge diversity of life-forms which are supported by the world of water is sequentially addressed, and the pattern of their dependence upon this ancient element of nature is sharpened and outlined.

PRF Brown
BCSLS {Freshwater}
Mountain Man Graphics, Australia

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E-Mail: prfbrown@magna.com.au

BY late afternoon banks of cumuli stretched in unbroken array across the plains, covering the foothills, their vanguards pressing against the first mountain slopes. Their progress partially checked, clouds and the whole layered air mass slowly began to rise. The ascent created a cooling effect that turned many droplets into ice crystals, which in turn robbed water molecules from adjacent droplets.

Cloud droplets and crystals, once infinitesimal and unaffected by gravity, now grew larger and heavier and fell whenever there was a momentary relief from the updraft currents, only to be caught and blown aloft again as the winds recovered. The droplets especially were growing steadily and the time was imminent when even strong winds could not prevent their return to earth.

The vertical winds lost their regularity and permanency, growing turbulent and disordered. At the bidding of the confused air currents rising over the foothills, clouds tore apart, re-formed, and piled upon one another, losing their individuality. Lost wisps of cloud swirled about the branches of trees on the shadowed mountain slopes beneath.

The sun still illuminated cloud tops, but it was sinking rapidly beyond the horizon, and the mountains and their valleys grew dark without the customary summer twilight allowed by a clear evening sky. As night drew upon the hills, the first rain came, hesitantly at first, then in drenching sheets which heralded the arrival of a great event. Trees tossed and strained, but soon the early downpour subsided, and rain fell throughout the remainder of the night, softly, without violence, in a gentle fashion, yet one that held enormous and unremitting power.

This was nativity, the birth of a river conceived in the southern sunlit ocean and nurtured in the womb of the sky. There was no fanfare for the birth of the giant, no roar or gusts of sleeting drops, but over the entire expanse of the hills there was a steady descent of drop upon drop. The easterly winds which had brought moisture- laden air inland still blew far above, releasing their water in droplets that descended in diminishing parabolas. The entire mass of falling water had a stilling effect upon the air, until in the lower regions rain fell straight toward its destination upon the mountain slopes.

Everywhere there was a whispering, as water, created of the earth, returned once more. Hour upon hour the rain descended, the abrupt arrival of each drop recorded when it struck ground or leaf, compressing the air in a sharp, fluid report. Small sounds radiated upward and outward, blending and losing all individuality, until to ears that heard, the forests and lower fields rustled with a pervading, welcoming murmur.

A raindrop, a million times the size of a cloud droplet, would have been a perfect, glistening sphere if surrounded by equal forces. But this could not be, for winds and changing pressures buffeted it so vigorously that its restraining surface film could hardly hold the water it contained, much less maintain the shape of a spheroid. As it began to fall, opposing pressures underneath cushioned its descent, causing the bottom to flatten out and even to become concave, while the remainder billowed out above in a trembling, ballooning mass. When the drop flattened out, it side-slipped, altered course, then again dropped straight down. Set in motion, a drop responded to both internal and external stresses until it oscillated and quivered like a living thing, alternating between a globule, a fat parachute, and a flattened disk.

A single drop, indistinguishable from its neighbors, collided and coalesced with other drops as it fell. Although it was repeatedly borne aloft again by the wind, its rate of descent, governed by its growing size, kept accelerating. When it struck a drop of similar size, both shattered into a spray of smaller droplets which began the falling and rising process over again. But the number of heavy drops increased, and soon many of them were clear of the cloud and fell directly to the earth.

The rain created a luminous halo around the distant hills, but overhead there was only a scudding darkness. Haze in the treetops muted the color and outline of their foliage and trees farther away were only faint outlines and at times totally obscured. Few drops struck the earth without previous interruption, but were intercepted by trees, shrubs, and low-lying grasses. When drops broke against leaves and splashed off, they multiplied into innumerable little droplets, causing the entire lower canopy of woodland plants to quiver as rain cascaded from above. Every seedling, every fern of the forest floor trembled in a rooted dance.

Leafy trees shed water quickly, but the evergreens, glistening with silver drops, held much of what they received between tightly spaced needles. Hemlocks displayed glassy spheres at the end of each of their tens of thousands of blunt needles. Heavy drops collected along fir branches, but left at drip points halfway along, falling to branches below. Streams of water clung to the underside of maple branches in crystalline ridges. Every twig, every stem and branch in the forest was wet with a thin layer of moisture, and the entire film flowed steadily downward along the trunks until it entered the soil where it diffused outward through the loose, absorbent forest floor. The leaf mold covering the soil became a rich, dark-brown carpet thick with captured water. Rocks jutting above the ferns turned a deep gray, and the lichens encrusting their sides no longer were dusty and dried, but grew green as the algae within drank in moisture. At the base of the rocks, the green of mosses deepened and grew richer, and the little plants straightened with water taken in through their delicate rootlike fibers. A cluster of reddish mushrooms glistened and swelled with succulence.

Whenever a large drop struck saturated soil, its compression created a tiny coronet of two dozen or more little spheres which shot into the air, then curved and fell spattering back, describing a dimpled circle around the original impact.

When each raindrop was finally stilled, its covering surface film immediately spread over soil particles and bits of vegetation, until every solid surface had stretched over it an unbroken layer of water. Underneath, the water flowed quickly between grains of sand and earth and spread through the countless galleries and internal spaces of the soil. Often it followed the hidden tracery of roots, filled the burrows of earthworms, and flooded the dwellings of ants, grubs, moles, and snakes.

Hour after hour throughout the night the forested hills drank in the rain. After the water had infiltrated the loose organic soil at the surface, it sank below the last humus layers and encountered sand and gravel. All particles in the soil, organic or not, accepted a film of water which clung fast due to molecular forces operating between the particles and the water. As the film increased in thickness, spaces were filled and air displaced, although air bubbles might be trapped beneath an impervious bit of clay or rock. The soil had been loose with air passageways which had permeated it, but now was becoming heavy and dense with accumulating water. Atmospheric gases, once plentiful in the soil, were diminishing. Some small subterranean lives tolerated the water, some welcomed it, but others drowned and suffocated from the lack of oxygen. A few crept into the rare air bubbles that remained, and were safe.

Not long after midnight the falling rain began to exceed the capacity of the soil to absorb it. Water accumulated on the surface as the overflowing ground refused it, then began to slip into small depressions where it collected in shallow pools. Rivulets carried masses of brown fir needles down their turbulent channels. The needles formed miniature logjams, creating additional pools until the dams gave way with a rush. As dams broke and pools spilled over, the water joined other streams until, when the level of encircling retaining elevations was reached, sheets of water slipped like quicksilver down' one gentle incline after the next.

When raindrops struck a pool's surface, small erect spouts jumped instantly from the point of impact. At the top of each spout, a tiny droplet broke free, shot higher into the air, and fell finally into the bombarded puddle of which it became a part. Occasionally when a drop struck water, a thin ring of muddy water arose, joined at the center, and trapped air in a large bubble which floated briefly until it was punctured by another raindrop.

The rain-soaked soil was of complex and varied nature. At the very surface was a layer of decaying organic matter, mostly vegetable in origin, but with some animal remains scattered about in the form of insect bodies, bits of bone, feathers, and other trivia. Beneath this, a layer of bacterial fermentation gradually shaded into rich organic humus which marked the lower limits of most roots and burrowing animals. Still farther down, the earth was composed of rock fragments, sand, and clay. The process of breakdown of minerals to smaller particles was an exceedingly slow one that had been occurring since the uplifting of the mountain slopes, two hundred million years before.

Water deep within the soil moved slowly. It sank down, percolating through the loose earth, where it touched upon a multitude of tiny lives which depended upon its presence. As water dissolved soil minerals, new conditions of acidity, alkalinity, and electrical charge were established, conditions affecting most of the small earth- dwellers. Mechanisms in the cells of roots began their chemical pumps, not only bringing in water but using it as a medium for the transport of dissolved minerals across their cell membranes. Fungi and bacteria emerged from spores minutes after being surrounded by the seeping water.

Bacterial populations in the soil were changing. Those requiring oxygen were giving way to others which became active only when that element was absent. This cessation of activity was only temporary, and later when the water would seep away, the oxygen-users would begin their life processes again. Bacteria in the soil had many functions: some worked upon mineral compounds of sulfur, nitrogen, and iron; some broke down organic compounds in the process of decay; and a few affected the growth of plants by producing antibiotics. In turn the bacteria were preyed upon by small soil animals, and attacked by viruslike bacteriophages, tiny motes which could destroy them completely by diverting a bacterium's own life processes. When conditions of moisture, temperature, and food supply became unfavorable, many soil bacteria could form resistant spores. At this moment in the wet earth, some bacteria were emerging from spores, while others were forming them.

Although many bacteria moved freely, their diminutive size prevented them from making headway against the slow currents as water flowed through the soil. By the billions they were carried from the surface to deeper strata, then horizontally as the ground water sought emergence at a lower level. No soil particle or interstitial space was without its own large and varied population of bacteria.

Throughout the soil, formerly inactive strands of fungus mycelium now grew vigorously, forming new branches from each of its delicate, gossamer threads several times in the space of an hour. Fragile as the strands of mycelium were, they penetrated the soil in all directions, most abundantly in the rich humus, but still significantly in poorer soils several feet below the surface. The primary function of mycelium was to absorb dissolved foodstuffs directly from the soil, but some of these fungi were engaged in trapping microscopic one-celled animals, while others caught active roundworms wriggling through the soil water from one crevice to the next. The latter fungi had grown small sticky loops from their mycelia; the random writhing of the worms assured eventual capture by coming in contact with the loops. Soon one captured worm after another became immobile and died as a result of a poisonous secretion from the fungal strands. The fungus then penetrated each worm with mycelial threads and carried on digestion by enzymes within the bodies of the animals.

Strands of other kinds of fungi produced ring snares into which the roundworms would crawl by chance. Upon the slightest touch, the cells composing a snare would swell instantly, lessening the inner diameter and choking the worm which failed to free itself. When the soil moisture later subsided and roundworms were no longer so free to migrate, the carnivorous fungi would return to a more commonplace existence and obtain nourishment in the usual manner from organic matter in the soil.

The ways of soil fungi were many and varied, with nearly every species having its own restrictions of food and environmental conditions. Some could break down organic material in the soil only after it had been worked on by another kind of fungus; others formed close relationships with more highly developed rooted plants. In these, the strands of mycelium either took the place of, or supplemented, the highly absorptive root hairs essential to plant nutrition. The mycelial threads provided an enormously complex network of cells which took in and conducted dissolved minerals to the roots of the larger plant. Now that water was flooding the soil, the activity of cooperative mycelia was at its height, and within each strand there was an increased flow of living protoplasm.

Among the first animals to respond to the saturation of the soil were microscopic one-celled protozoans: amoebas which crawled about carrying delicate urnlike cases into which they could retire; flagellates that would stay active until the last vestiges of water disappeared; dwarf ciliates speeding through water-filled spaces with thousands of synchronized beating cilia. Later, when the soil dried out, both ciliates and flagellates would encapsulate themselves in resistant cysts, but a house-bearing amoeba would simply retreat into its case and plug the hole, very much as the far larger land snails in the forest litter would do. Some of the protozoans fed upon organic matter in the soil, but the greatest number devoured living bacteria swarming in the soil water, swept down from the highly productive surface layers of organic debris.

Other grotesque creatures were present, scarcely larger than the soil particles they lived among. There were shiny, translucent mites with eight legs creeping carefully about; the omnipresent roundworms wriggled with increased activity now that the boundaries of their world had enlarged to a virtual infinity; water bears used their four pairs of clawed legs to wedge themselves from one cavity to the next; and rotifers unfolded beating cilia to create a fluid vortex which swept into their beating jaws bacteria and one-celled plants suspended in the water.

In the wide, humus-filled crack-of a large boulder, a small fungus with tiny cuplike reproductive structures was being struck repeatedly by raindrops. When a drop hit the center of a cup, it splashed out countless spores that fell to the moist leaf mold some distance away. On the side of the same boulder, a red-capped lichen swelled with water and grew greener as its pkarasitized algae glowed through the wet fungus filaments making up the simple plant. At the base of the rock, the coiled sperm of male moss plants emerged and with long writhing flagella swam through the water film covering the bed of moss. Some of these sperm eventually would find an egg in one of the female plants, drawn to its receptacle by secretions from special surrounding cells.

From a rotten log, once nearly dried out but now a moist and pulpy mass, a slug crawled from its slime cocoon that had prevented desiccation, and inched slowly toward the ground, leaving behind a cluster of glass-clear eggs. In the same log, a red-backed salamander crept to the surface through a tunnel excavated long ago by a wood-boring beetle. At the entrance the small lungless amphibian waited with staring, protruding eyes as raindrops stirred the scene outside the log.

Another amphibian, a spadefoot toad, erupted to the surface of the soil, heaving earth out of the way as its stout body emerged from the subterranean retreat it had occupied during the past dry weeks. With small clods of mud still adhering to its yellow and black skin, the toad raised its head high, inflated a white ballooning throat, closed its eyes, and called into the night a penetrating, nasal "wank! " -to be answered at once by an identical call from a temporary puddle not far away. As the night rain continued, spadefoot toads appeared over the hillsides, met, mated in the shallow pools where females laid their eggs on plant stems, and returned to the earth, digging deep before the soil could dry out.

Beneath the soil, in a long wandering tunnel, a mole pushed its way with heavy, scooplike front feet, twisting its body so first the roof and then the sides of the burrow were packed tight. Then, turning a slow somersault in the narrow space, the mole retraced its path, stopping now and then to shake moisture from its fine, dense fur. Its deeper living quarters were completely inundated, and even the surface foraging tunnels at times were filled with water through which the mole had to pass quickly, its fur glistening like silver with trapped air. Blind though it was, it was hunting, for its other senses were keen. Normally it would hunt most actively in the daytime, when insect activity was greatest, but tonight as the soil filled with water, earthworms, grubs, millipedes, and centipedes began heading for the surface where there was a greater supply of oxygen. Their progress frequently was terminated by the mole as it scrabbled excitedly in search of victims which penetrated its burrow. Upon finding a beetle, it pressed the insect against the wall of the tunnel with one of its front feet, while it bit off the head and then began to devour the whole insect. Later, it came across a large earthworm which it dextrously manipulated until, starting at the front end, it consumed the whole length of the worm with sharp conical teeth and jaws working furiously.

In the soil under a bed of ferns were two animals which bore superficial resemblances to the mole and earthworm, but came from widely different ancestries. A dark-brown mole cricket, with powerful, enlarged front legs, shoved itself through the earth in the same manner as the much larger mammal. Water-filled tunnels had little effect upon this insect, for it carried a coat of air trapped by many short hairs distributed over its body. The other creature was a close mimic of an earthworm, but in reality was a snake, a small burrowing worm snake which, like the mole, was finding hunting more profitable than usual.

Across the forest floor small annual seed plants showed the effects of water absorption. Their delicate stalks grew turgid and straight, while their leaves flattened and were held out stiffly into the night air. Each leaf was struck repeatedly by raindrops which fragmented and splashed in a fine spray about the plants. By absorbing soil water, woody shrubs and trees were making preparations for the day to follow when the sun's energy would set into motion a vast and complex system of water transport within their trunks, ultimately releasing to the atmosphere individual water molecules by evaporation.

There was no single fate for the water which fell to earth during the night. What happened to a raindrop was determined by chance at the moment of impact. Some water seeped into the soil and flowed parallel to the surface, only to emerge as a spring farther down the hillside. Other drops continued to sink into the soil until they were trapped beneath deeply buried rock layers. Under such an impervious ceiling the filtered water would continue to flow very slowly, taking a thousand years or more until it broke free of its confinement under a distant sea.

The rain stopped in the early morning hours, but the murmuring of water dripping from millions of leaves went on, gradually diminishing. When it finally ceased, a heavy silence blanketed the forest. A single delayed drop, hesitating, plunged into a still pool below and broke the quiet with a sharp musical note.

A tiny, isolated world, replenished by the rain, consisted of a deep hole in the trunk of a beech tree, created years ago when a branch had broken off, leaving the heartwood exposed. Bacteria of decay had carved out the niche which extended down a foot or more into the thickened base of the tree. The lips to the hole were healed over with rounded bark and the cavity inside was carpeted by a spongy layer of rich organic humus. The treehole contained multitudes of organisms, populations, and interrelationships quite distinct from those found elsewhere in the vicinity. It was a world in itself.

A small black ant, having been caught far from its nest, emerged from the shelter of the treehole and crossed the damp earth in search of the obliterated scent trail it had followed before the rain. From time to time the ant paused, raised its head and body high on the last two pairs of legs and, with the front pair, scraped its antennae clear of moisture and adhering fragments of damp earth and vegetation.

A screech owl clung to the lip of another hole high in a dying oak, fluffed out its feathers and shook off a fine spray of moisture. It looked about attentively, gave its wavering, chuckling cry, and launched itself into the dark. One last nasal call of a spadefoot toad signalled the completion of its night of activity, and it joined the others of its kind beneath the wet soil. In the distance, a gray sky foretold the end of the night.

The sun rose in a cleared sky and illuminated the mist still clinging to the wet mountain slopes. Every tree and bush, all grasses and ferns, spider webs, rocks, and the soil itself, gleamed with refractive liquid jewels which caught miniature images of the sun and focused them back into the sky. Against the silence, calls of birds poured out.

Within the first hour of daylight, the sun shone through the still air with increasing warmth and intensity. Drops on every surface grew smaller as water molecules escaped through their surface film to become aerial vapor. A worker honeybee, on its way to a clover-filled clearing, landed on a raspberry leaf and sipped a water droplet. During the second hour, as drops hurried toward extinction, the glistening tracery of the earth and its vegetation abruptly vanished. A chipmunk ran the length of a fallen log, tail flicking, then sat at the end in a sunbeam, scrubbed its face and scratched vigorously.

Rain puddles lay about in profusion, but had begun to shrink. In part, this was due to further absorption by the soil, but mostly it was the result of evaporation into the increasingly receptive air. By noon only the largest pools would remain.

The enormous amount of area presented to the air by soil particles lying close to the surface allowed a continuing loss of water by evaporation. As the uppermost layers dried out, capillarity drew streams of cohesive water upward from the saturated depths, then this too left for a free existence in the atmosphere. Fully a third of the water that had fallen the previous night was in the process of returning to vapor, while a lesser amount was seeping through the soil, seeking emergence in lower lands.

With the sun pouring out radiant energy, green plants commenced their biochemical activities again, now even more accelerated by the abundance of water in their tissues. Through every seed plant, large or small, ran countless vertical streams of water, enclosed in tubes extending from the depths of the roots to the edges of leaves. Each tube, made of many dead cells and strengthened by thick walls of woody fibers, began far underground, close to regions where millions of tiny hairlike cells grew into the soil from each root tip's surface. It was only through these root hairs that water entered the plant from the soil. Short though they were, the numbers of these tiny hairs were so great even in a little plant that, if placed end to end, they would stretch many miles. In effect, each plant had miles of water absorbing filaments in a single cubic inch of soil, making every plant of the forest highly efficient in the capturing of this precious fluid. Water entered more freely by diffusing from a region where it was abundant to another-the root hair-where it was not so concentrated. With the flow of water came all the dissolved minerals the plant would need, drawn into the root hairs by positive and negative properties of both minerals and cells.

The long conducting tubes of root and stem contained a watery sap in an unbroken column, exposed to the air at its uppermost terminal in a leaf. As the warming air encouraged evaporation, the tiny exposed surfaces of each column released a few water molecules at a time. In this way, a column of water, bound by cohesive forces, was gradually lifted by a sun engine.

For most of its journey, a column carried with it the dissolved nutrients brought in from the soil by the absorptive root hairs. These mineral foods debarked upon chemical demand in the leaves, but much of the water followed a one-way course and passed into the air from which it had come not many hours before, spraying out into the atmosphere in invisible fountains of vapor.

The water columns had been still during the night when the air was saturated, but now they moved steadily faster, drawn by the demand of twigs, leaves, and the heated air. Later in the day, when the air grew cooler and evaporation lessened, the rate of ascent would slow and even stop if the night proved to be humid.

Not all the water left the leaves, for it was needed to furnish strength by keeping cells turgid and bathed in the same aquatic environment from which all plants originated in the distant past. It also had to carry back down to stems and roots the rich concentrates of food that had been produced in the leaves by sun energy and green chlorophyll. The descent of food in small linked tubular cells just beneath the bark of leafy trees was a source of nourishment to many animals, large and small. In some of the trees, beetles were chewing their way through the bark; in others, tiny aphids were fixed in place as their needlelike mouthparts pierced an individual tube. Some of the smaller trees bore fresh scars where hungry porcupines had eaten into the nourishing tissues, or where deer had stripped bark off in long ribbons. The thick sap flowed down slowly, only two or three feet an hour, pulled down by the need of cells in the lower portions of a plant, for this was the only food of all the actively growing cells of root, trunk, and branch.

The single most important role played by water in the forest was in the chemical production of food in leaves. Here water molecules were split asunder by certain wave lengths of radiant energy from the sun, the process controlled by a large, tadpole-shaped molecule of chlorophyll. Of the two elements released by the separation of each water molecule in a cell, oxygen was set free in large quantities, but the hydrogen was passed along a series of energy traps. Later the hydrogen would be locked together with carbon dioxide molecules from the air to build a sugar that would not only supply the plant with its energy requirements, but would form the basis of food for animals that might graze upon its leaves, twigs, fruits, or strip away its bark. Food manufactured by green plants provided the basic energy for all living things, for those animals unable to eat plants directly were links in a chain of predators in which the first creatures were always vegetarians or scavengers. In this way, the water which had fallen to earth became an integral part of every living thing in the forest.

During the night, water running off the saturated earth had created rills and gullies, and filled small rocky stream beds. Further contributions to the young river would be made for days by water emerging gradually from porous stream banks. When water rushed down mountainsides and streamed across the hills, it drew upon soil water, but when the earth dried out, small streams were obliged to return water to capillary spaces of the soil, and in doing so might easily give up their very existence. The river had been born and its growth now began. Like the elements of its diffuse creation, it still had no unity, but flowed excitedly in divergent rills and beds. Seeking lower levels, the water tumbled down, rills joining gullies, and gullies emptying into brooks. From a million separate origins, from rock funnels or meadow wetness, the river was beginning to gather and to assume the promise of a mighty identity.