Organic Matter In Soils
From the time plants first ventured out of the protecting waters of the sea, there has existed a kinship of soil, organic matter and plant life which has continued down through the ages. Even before the first feeble formation of land began, the processes of soil devel­opment were well under way. For millions of years, mineral elements had been accumulating: sand and gravel flaked away from rocks high in silicates; wind, water and frost disintegrated various oxides into clay, and sedimentary layers lifted above the seabed and gave up their lime.

These accumulations of rock debris were not, however, true soils. Plants, microorganisms and organic matter-life elements that had not yet appeared on dry land-were necessary for the formation of true soils.

No fossils remain today to give us a picture of the first "plants" that crept slowly out of the waves and onto the rock. Soft, without skeletal structure or fiber, these plant forms left behind no clue of how they were able to escape their dependence upon the sea. Eon after eon must have passed before one form less fragile than the rest was at last able to leave the protecting waters and establish itself permanently on dry land.

From here on, the record is easier to read, since the descendants of these primordial bits of vegetation still cling to the rocks at the ocean's edge-the lichens that grow much as their ancestors did millions of years ago. Primitive in structure and function, they ask little of their environment. Their life-cycle helps to form soil today just as it did then. Since lichens have no roots, they have no need for soil. Instead, their hold-fasts cleave to the naked rock, emitting an acid that dissolves the stone beneath them, releasing solutions of minerals on which they live. Some of the rock resists dissolution, leaving harder grains that tumble down the slope to collect in hollows at the base. The lichens themselves die, crumble to dust and join the mineral build-up at the base. Fungi and bacteria invade to feed upon this pile of mineral and plant matter, and thus does the world's stock of soil increase.

In the course of checking various reference works and subject-index-files, I noted nearly 850 different phases of organic matter and their relation to soils and plants. Many of these phases would easily occupy a full chapter, while others could not be adequately treated in anything less than a full-length book.