^ Preface 



posal to use the term 'micro-nutrient element' to replace such terms as 

 'trace element,' 'minor element' etc. 



Four papers presented are of importance in focussing attention on the 

 functions of trace elements in the metabolic processes of plants. 



E. G. Mulder described his investigations relating to the eflFects of 

 copper and molybdenum on As'pergillus niger and on higher plants, and 

 indicated the role of molybdenum in the reduction of nitrate in plants 

 and in the fixation of atmospheric nitrogen by Azotohacter. Similar results 

 for nitrate have been obtained by other workers and Nicholas,"' using 

 Mulder's strain of Aspergillus, has been able to prepare standards to de- 

 termine the availability of the trace elements Cu, Zn and Mo in soils, and 

 has applied the method with success in investigating instances of deficiency 

 of these nutrients. These studies on molybdenum have already found im- 

 portant applications in agriculture, in Australia, New Zealand and Great 

 Britain.^^-'-^'" 



J. Lavollay has also used Asfergillus niger in his studies to determine 

 the coefficient of action of mineral nutrients, and has been able to demon- 

 strate quantitative interactions of nutrients and similarity of action between 

 potassium and rubiditmi. This last point is of interest in connection with 

 investigations of G. and D. Bertrand,*^' reporting the widespread occur- 

 rence of rubidium in plants. 



J. Erkama described comprehensive investigations relating to the r6les 

 and interactions of copper, manganese and iron. He concluded that Cu 

 and Mn react differently on iron, reactions with the former occurring on 

 the protoplasm and wath the latter in the vacuole sap. Erkama, like many 

 other investigators, believes that relationships of nutrients must be studied 

 in attempting to determine their individual functions. In this connection 

 the complexities of such investigations must be stressed and the difficulties 

 that arise in distinguishing between reactions occurring in the substrate 

 and within the plants. 



H. BuRSTROM discussed experiments relating to the action of nitrogen, 

 manganese and phosphorus on roots, in which he has been able to distin- 

 guish separate effects for each element. FoUovdng from the results ob- 

 tained with manganese and nitrogen, it would appear of interest to extend 

 the work to include molybdenum, and to examine the interactions of man- 

 ganese and molybdenum in view of their special relationships in acid 

 soils."' 



Trace element problems in crops occurring in European countries were 

 discussed in five contributions. 



L. Gisiger described the conditions associated vdth crop failures in 

 Switzerland during the war due to deficiencies of boron and manganese 

 respectively. Overliming was of importance in causing or accentuating 

 these difficulties. Gisiger concluded from his experiments that the dam- 

 age caused by overliming results from the action of the increased concen- 

 tration of the OH • anion. The anion exerts a hydrating action on the 

 plant roots which boron tends to counteract. Boron deficiency effects re- 

 sult when the OH " anion is in excess in relation to boron. In the case of 

 manganese, the OH ■ anion is regarded as reducing the availability of man- 

 ganese over an intermediate range of pH. 



It may be noted that alternative hypotheses have been advanced to 

 explain the lime effect in both cases."*"' 



