Page:History of botany (Sachs; Garnsey).djvu/521

] elements in the modern theory of the respiration of plants, though he did not fully explain their mutual connection.

It evidently was the received opinion before the time of Ingen-Houss, and in spite of Hales' views, that plants derive the larger part of their food from the constituents of earth and water. lUit when it became known that the carbon, which is the chief constituent of vegetable substance, comes from the atmosphere, and it was considered that much the larger part of that substance is combustible, it naturally became a question whether the incombustible ingredients which form the ash take any part in the nutrition of plants. This question was by many physiologists answered in the negative; but de Saussure maintained the contrary view. He insisted that certain ingredients, which are found in the ash of all plants, must not be regarded as accidental admixtures, and that the small quantities in which they occur are no proof that they are not indispensable; and he showed from a large number of analyses of vegetable ash, which for a long time were unsurpassed in excellence, that there are certain relations between the presence of certain substances in the ash and the condition of development of the organs of the plant; for instance, he found that young parts of plants capable of development were rich in alkalies and phosphoric acid, while older and inactive portions were richest in lime and silicic acid. Still more important were the experiments in vegetation, by which he showed that plants, whose roots grow not in earth but in distilled water, only take up as much ash-constituents as corresponds with the particles of dust which fall into the water; and further, that the increase in the organic combustible substance of a plant so grown is very insignificant, and consequently that there is no normal vegetation where the plant does not take up ash-constituents in sufficient quantity, a result of the highest importance to the main question. Unfortunately de Saussure neglected to state these results with due emphasis and to point out their fundamental importance, and consequently doubts were enter-