Abstract
It has long been recognized that the incombustible residue resulting from the incineration of a plant is of great importance, and a large amount of work has been done to determine the chemical combinations resulting from the incineration, since by this means it was hoped to determine the nutritive elements which are essential to the plant. This method has proven only partially successful. Liebig (I855), basing his conclusions upon water culture methods, advanced the view that certain salts are indispensable to plant development and maintained that the productiveness of the soil is determined by the essential salts present. Liebig's hypothesis stimulated research, and it was later determined that six ash constituents are essential to the growth of phanerogams, viz., calcium, magnesium, potassium, sulphur, phosphorus, and iron, to which should be added nitrogen, a constituent not found in the ash. Many similar experiments confirmed these results, but the general trend of investigation soon changed to the study of the function of the elements thus shown to be essential. Various writers, more recently Chirikov (I9I4) and Truog (I9I6), have attributed to calcium the function of acting as a carrier of the essential phosphoric acid and as a neutralizer of the organic acids formed in protein synthesis. In agreement with several early workers, Hansteen (I9IO) has described calcium as functioning in the transformation and transfer of carbohydrates and in the formation of cell walls by green plants. On the other hand, Robert (I9II, I9I2), confirming the results of earlier investigators, has shown that calcium is not an essential element in the nutrition of fungi, and Molisch (I895) has found that certain algae can thrive without calcium. The effect of calcium in reducing the toxic action of other bases, notably magnesium, in the culture solution has been studied especially by Loeb (I906), Osterhout (i9o6a, i908, I9II, I9I2, I9I6), and McCool (I913).
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