64 



TRACE ELEMENT DEFICIENCY 



Some good colour photographs of both sugar beet and red 

 beet affected with the disease are given by Wallace (1943, 

 pp. 97-9, plates 81-5). 



The attribution of speckled yellows to a deficiency of man- 

 ganese is chiefly based on the fact that the disease is cured by 

 applications of a soluble manganese salt. Analyses carried out 

 by the writer and Dr K. W. Dent, however, show a very 

 striking difference in the manganese content in normal and 

 affected plants of sugar beet. The affected plants examined were 

 grown by Mr W. Morley Da vies on soil which had been heavily 

 limed in order to induce manganese deficiency. The normal 

 plants were grown on an adjoining plot not subjected to heavy 

 liming. The differences in manganese content of healthy and 

 affected plants are clearly shown by the data in Table II. The 

 values marked £> were obtained by the polarograph, those marked 

 a by the absorptiometer. 



Table II. Manganese content of normal 

 and speckled sugar beet 



Manganese content in p. p.m. dry matter 



Although the determinations by the two methods show in 

 some cases a little divergence, they make it clear that the 

 plants affected with speckled yellows contain considerably 

 less manganese than normal plants. This is particularly so 

 in the leaves, where the manganese content of the speckled 

 plants is of the order of one-tenth that of healthy plants. The 

 data afford supporting evidence for the view that speckled 

 yellows is a manganese deficiency disease. 



Marsh Spot of Peas. The symptom of the disease of peas 

 known as marsh spot is the occurrence on the seeds in the pod 

 of brown or black spots or cavities on the internal surface of the 



