The soil is the source of all of their supplies except sunshine and air. The available water is a function of soil type and weather. The soil, friendly provider, can also be an antagonist, clinging grudgingly to moisture needed by the plant. Soil types differ in their ability to retain water against gravity and release it to plants. Mineral content of soils also varies.
Plants require some minerals in fairly large amounts and some in small amounts.
The presence of those needed in only trace amounts is just as critical as it is for those needed in large amounts. Once the water and minerals are acquired, the logistical problems are far from over. The mechanism for movement of materials from roots to the uppermost shoots baffled scientists for ages. It was no less difficult to explain the movement of sugar from the site of photosynthesis to the site of need or storage. These mysteries are explained in this chapter.