This section is from the book "The Gardener's Monthly And Horticulturist V18", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
The number of metals absolutely indispensable to all plants, and consequently to fruit trees, is six; namely, potassium, calcium, sulphur, phosphorus, manganese, and iron. There is no doubt, however, that certain plants require, in addition to these, this or that other metal to complete their nourishment. We may even assume that silica, chlorine and sodium, and perhaps also magnesium, play a part in the functions of certain plants. If we reckon the four gaseous elements which furnish plants with their first and principal food, we have a total of ten, or sometimes thirteen or fourteen elements, which have proved essential to the perfect development of plants. According to Prof. Adolph Mayer's excellent text-book of agricultural chemistry, these elements are taken up in the following forms: - 1, as free oxygen; 2, as water; 3, in the form of acids, namely, a, as carbonic acid; b, as nitric acid; c, as sulphuric acid, and d, as phosphoric acid. 4, in the form of bases, namely, a, as potassium; b, as calcium; c, as manganese, and d, as oxide of iron.- Journal of Chemist)-}/.