Botany
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Plant physiology
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Plant physiology
Plant physiology as a science has recent origins; however, observations on the vital phenomena of plants are already found among the ancients. Aristotle and his disciple Theophrastus, author of De causis plantarum, believed that plants derive nutrients from the earth already in a directly assimilable form. This conception, partly resumed by Cesalpino, practically dominated until the sixteenth century, when, taking advantage of the progress of chemistry and physics, were started the first studies on experimental basis on the process of nutrition of plants, the circulation of sap and the transport of substances in the form of solution. J. B. van Helmont, based on his experiences, believed that the various constituents of plants were manufactured by the plants themselves.
E. Mariotte tried to trace the nutrition and growth of plants to chemical or physical processes. Fundamental for the development of plant physiology was the work of S. Hales, who carried out a series of systematic experiments on the problem of lymph circulation, highlighting the role played by the transpiration of leaves and discovering the root pressure. The function of chlorophyll was highlighted towards the end of the XVIII century by J. Priestley, who demonstrated that green plants are capable of emitting “vital air”, that is oxygen. G. Ingenhousz completed this observation by noting that only the green parts of plants and only in the light develop “vital air” and then gave the exact interpretation of the phenomenon using the discoveries of A.-L. Lavoisier.
The set of gaseous exchanges that take place in plants were further clarified by J. Sebenier, who recognized that carbon dioxide is decomposed by plants, under the influence of light, with the emission of oxygen. At the beginning of the XIX century T. de Saussure performed precise experiments that allowed to evaluate in quantitative terms the phenomena that occur during nutrition. H. Dutrochet discovered the fundamental laws that regulate the permeability and osmosis phenomena, later specified by W. Pfeffer.
The plant physiology drew new impetus from the studies of J. Sachs that, in a group of works published between 1860 and 1865, recognized the general significance of photosynthetic processes and clarified how and where the organization of carbon dioxide occurs until the formation of starch. Research on mineral nutrition were initiated by J. Liebig and later by J.-B. Boussingault, who demonstrated the importance of nitrogenous substances, and especially nitrates, for plant life. In 1887 H. Helbriegel and H. Wilfarth discovered the biological fixation of nitrogen.
With the XX century begins a new period for plant physiology: they discovered common phenomena that had gone unnoticed (photoperiodicity) as well as the existence of hereditary physiological characters; they isolated substances that regulate the development; they discovered many enzymes and, using the technique of marked elements and chromatography, they clarified the process of photosynthesis. However, it is difficult to make a separation between plant physiology and biochemistry, sciences that, together with genetics, have increasingly contributed to the emergence of molecular biology, while the links between plant physiology and ecology become closer.
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