67 LoHNis: Excess of Manganese 



When the symptoms were most conspicuous (June 27) a very 

 distinct difference was found between the content of manganese 

 in healthy and affected plants. All samples with a content of at 

 least 1210 p.p.m. Mn, in dry matter, were affected, all those with 

 a lower content (max. 536 p.p.m.) were healthy. The level of 

 1210 is shown with a dotted line in all figures with the results of 

 1946 observations. 



The samples collected on July 12 were taken to see whether 

 the partial or total recovery of the beans would coincide with a 

 lower content of Mn if compared with affected material. In 

 most cases, indeed, the content was lower. Several times, how- 

 ever, the content surpassed 1210 p.p.m. (plot 10 kg, j?H 5.0, 1598 

 p.p.m. Mn), while the foliage did not show any symptoms. More 

 mature beans appear to tolerate a higher content of manganese 

 without showing any injury. 



In 1947 samples were taken on June 6, when the plants, being 

 very yellow and poorly developed (Plate 8a), were severely 

 affected, and on July 9, when many plants showed recovery. 

 Only part of the samples has been analyzed as yet and the results 

 are given in Figure 8. The lowest content of Mn found in 

 affected foliage was 1285 p.p.m., near the threshold value found in 

 1946. The border line at the 1285 p.p.m. level has been shown 

 in all figures relating to 1947. On July 9, recovery had progressed 

 markedly. The Mn content of all samples was lower than on 

 July 6. The last columns represent the values for a single plot, 

 the southern part (S) of which was strongly, while the northern 

 part (N) was only slighdy affected. The plants on the South 

 side hardly differed in content from that found on June 6. 



Figure 9 shows the amounts found for a number of years in 

 material from healthy and affected plants grown on the same 

 fields, often from special sections. In all cases studied there exists 

 a very definite difference in Mn content and the occurrence of 

 injury coincides always with a high manganese content. 



During the years this phenomenon has been studied in beans, 

 potatoes were grown on one half of each plot and in some years 

 the whole or half of a row has been planted with other crops as 

 strawberries, oats, tobacco, cauliflower. None of these crops 

 showed any symptoms of injury. As far as their foliage has been 

 analyzed for manganese, the results are shown in Figures 10 and 

 11. Strawberries have a much lower Mn content than beans. 

 They rarely surpass the "danger line" of 1210 p.p.m. for beans. 



