Wallace: The Method of Visual Diagnosis 



cesses of the two trace elements manganese and aluminium are 

 likely to be of importance in the soil acidity problem for these 

 crops (10). Thus for potatoes neither appears of great impor- 

 tance, calcium deficiency being the major factor, though manga- 

 nese toxicity effects are sometimes evident in the field. With 

 cereals, excesses of both aluminium and manganese are important, 

 particularly for barley but only slighdy for oats. For many of 

 the Brassicae manganese toxicity is a serious factor, but calcium 

 deficiency may also be important, and the two effects may occur 

 together. For runner beans manganese toxicity is responsible for 

 the prevalent effect of 'Scald' (8). In the case of sugar beet, 

 complete failures are often associated wdth the excess aluminium 

 type of plant, but the motded chlorotic condition which results 

 from manganese toxicity is also of common occurrence, whilst 

 calcium deficiency is only rarely observed. 



Conclusion:— In introducing to you for discussion the subject 

 of the application of the visual method to trace element problems 

 of plants, I should like to emphasise the fact that at Long Ashton 

 we realise clearly that the visual method has its limitations and is 

 most effective when used in conjunction wath other recognised 

 procedures. I trust, however, that the points I have brought 

 before you will serve to show that the visual method can provide 

 valuable data in the investigation of many problems of plant nu- 

 trition in which trace elements are concerned. 



Effects produced by deficiencies, excesses, relationships of trace 

 elements and of soil acidity factors, described in the above text, 

 were illustrated by numerous photographs from sand culture ex- 

 periments carried out at Long Ashton Research Station. 



References 



1. Wallace, T., 1943, 1944: The diagnosis of mineral deficiencies 

 in plants— a colour atlas and guide (London: H. M. Stationery Office). 



2. Hewitt, E. J., 1945: Long Ashton Ann. Report, p. 50. 



3. Hewitt, E. J., 1946: Long Ashton Ann. Report, p. 51. 



4. Hewitt, E. J., 1948: Nature 161:489. 



5. SoMERS, I. I. and SmvE, J. W., 1942: Plant Phys. 17:582. 



6. Pbabse, H. L., 1944: Farmg. S. Africa 19:688. 



7. Jones, E. W. and Hewitt, E. J., 1949: Long Ashton Ann. Report, 

 p. 49. 



8. Wallace, T., Hewitt, E. J. and Nicholas, D. J. D., 1945: Na- 

 ture 156:778. 



9. Wallace, T., Davies, W. M., Nicholas, D. J. D. and Hewitt, 

 E. J., 1946: Long Ashton Ann. Report, p. 61. 



10. Hewitt, E. J., 1947: Long Ashton Ann. Report, p. 82. 



