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This review is concerned primarily with the nature and origin of the forces bringing about movement of water from soil or other media surrounding roots into the conducting elements of the xylem, and with those internal and external factors which affect the rate of such movement. Absorption of water is not an independent process, but is closely related to other processes included in the domain of plant water relations. The rate of water intake is markedly affected by the rate of transpiration and by the extent and condition of the root systems. It is also affected by such environmental factors as the available moisture content of the soil, soil temperature, soil aeration, and to a lesser extent by the kind and concentration of ions in the soil. Some phases of the work discussed in this review naturally are incomplete and do not permit formulation of definite conclusions concerning certain aspects of the absorption problem. Where the writer has drawn conclusions or made generalizations they seem to be those most justifiable on the basis of the available evidence. It is realized, however, that as knowledge of these processes increases it may be necessary to modify some of the present conclusions. It is impossible to cite all the literature, but most of the papers cited have bibliographies in which the reader can locate other papers dealing with any particular phase of the field.

The present paper is the continuation of a previously published work, (Havre & al., 1960), on the study on conditioned and simple copper deficiency in cattle and sheep in Setesdalen, a valley in the South of Norway. In order to verify molybdenum as a conditioning factor, the fluctuations of the content of molybdenum and copper in the grass during the summer season 1959 have been studied. It was found that the content of both molybdenum and copper increased during the summer and reached its highest values in the first part of August. As stated in the previous paper, the conditioned copper deficiency in Setesdalen was proved to be a disorder occurring on autumnal pasture. From the clinical material collected during the years 1958–60, it may be concluded that the simple copper deficiency in Setesdalen occurs only in the winter season, on stallfeeding. This corresponds fairly well with the fact that the copper content of the herbage has its lowest value about the first of July, the time for grass-mowing in Setesdalen. The seasonal variations of copper and molybdenum were compared with statistics of the precipitation in the investigated areas in the same summer. The content of molybdenum as well as copper in grass was found to be lower in 1959 than in the previous years, probably due to the dry summer in 1959. The molybdenum figures, however, are still above 3 p.p.m. in herbage from areas with conditioned copper deficiency, and the copper figures below 5 p.p.m. in areas with simple copper deficiency. These concentrations were in the first work, in accordance with Cunningham, stated as the “dangerous” limits. In the present work, spectrographs analyses of a series of elements, altogether 18, are carried out on grass samples collected in the summer of 1959. The etiological importance of the various elements is discussed and particular attention is paid to sodium, manganese and sulphur. Sulphur is treated more thoroughly, as the whole herbage material from 1958 has been analysed on total as well as on inorganic sulphur (sulphate), in order to study Dick’s theory on sulphur as a conditioning factor in the syndrome of conditioned copper deficiency. The results of the analyses, however, give no support for sulphur as a conditioning factor in Setesdalen. A hypothetical “copper favouring factor”, possibly vitamin A, is discussed. The clinical observations are discussed in relation to the analytical results. Den foreliggende artikkel er en fortsettelse av et tidligere publisert arbeid om forekomsten av betinget og enkel koppermangel i Setesdalen (Havre & al., 1960). Det naervaerende arbeid har gatt ut pa a verifisere molybdenets virkning som en betingende faktor ved a undersoke svingningene i vegetas jonens innhold av molybden og kopper gjennom sommersesongen 1959. Det ble konstatert at innholdet av bade molybden og kopper steg utover sommeren, og nadde sitt hoydepunkt i forste del av august. Den betingede form for koppermangel i Setesdalen ble i forrige arbeid vist a vaere en beitesykdom pa hostbeite. Det samlede kliniske materiale fra arene 1958–60 har vist at den enkle koppermangel utelukkende forekommer pa inneforing i vinterhalvaret. Dette korresponderer bra med at kopperinnholdet i vegetas jonen viser seg a ha sin laveste verdi ved slattetider omkring 1. juli. Kurvene over molybden- og koppervariasjonene i gras ble ogsa sammenholdt med en nedborsstatistikk for de undersokte omrader samme sommer. Det har vist seg at de fundne verdier i gras for savel molybden som kopper, i denne sesong la lavere enn arene for, hvilket antakelig skyldes den torre sommer i 1959. Verdiene la imidlertid fremdeles over 3 p.p.m. molybden i omrader med betinget koppermangel, og under 5 p.p.m. kopper i omrader med enkel.koppermangel. Disse konsentr as joner ble i forrige arbeid, i overensstemmelse med Cunningham, karakterisert som de „farlige” grenser. I det foreliggende arbeid er ogsa utfort spektrografiske analyser av en serie elementer, tilsammen 18, i gras som ble samlet inn sommeren 1959. Betydningen av de forskjellige elementer i relasjon til forekomst av koppermangel-syndromet er droftet, og oppmerksomheten rettes saerlig mot natrium, mangan og svovel. Svovel er behandlet mer inngaende, idet hele vegetasjonsmaterialet som ble samlet inn sommeren 1958 er analysert pa bade total-svovel og uorganisk svovel (sulfat) ; dette for a forsoke a verifisere Dick’s teori om svovel som en betingende faktor ved den betingete koppermangel. Analyseresultatene gir imidlertid ingen direkte stotte for at svovel virker betingende under de radende forhold i Setesdalen. En hypotetisk „koppervennlig faktor”, muligens vitamin A, er droftet. De kliniske observasjoner er droftet i relation til de analytiske resultater.