Rothamsted Symposium on Trace Elements 36 



This test permitted the detection of 0.0005 mg and, with special 

 care, 0.0001 mg of the combined content of a group of metals: 

 zinc, copper, nickel, cobalt, lead, mercury, cadmium, thallium 

 and bismuth. The purification procedure reduced the metal con- 

 tent of the nutrient salts from 0.5-5.0 to less than 0.01 parts per 

 million, and the redistillation reduced the metal content of dis- 

 tilled water from 0.010-0.100 to less than 0.001 p.p.m. Each lot 

 of water and stock solution of chemicals was tested and, if found 

 pure, approved for future use in the preparation or replenishing 

 of nutrient solutions. The purified chemicals and water could 

 thus be added independently of each other, to give nutrient solu- 

 tions of equal and reproducible purity. It was possible, using 

 this technique, to obtain consistent and reproducible responses in 

 plants from adding minute amounts of metals to the nutrient 

 medium (for example, 1 part of zinc in 200,000,000 parts of cul- 

 ture solution, which amounted to 0.001 mg of zinc to a plant). 



When tomato plants were grown from the seedling stage in 

 nutrient media purified in this manner and supplied with a com- 

 plete nutrient solution including the four micronutrients B, Mn, 

 Zn and Cu, characteristic deficiency symptoms became apparent in 

 a few weeks (2). The lower leaves developed a distinct mot- 

 tling, different from any other deficiency symptom previously 

 noted in the tomato. In latter stages, necrosis at the margins and 

 a characteristic involution of the laminae accompanied by abscis- 

 sion of blossoms were noted. Thus it was found that by the first 

 criterion of essentiality, the completion of the life cycle, the nu- 

 trient medium was deficient in some essential element. Com- 

 plete recovery was obtained upon adding the B7 solution. A 

 breakdown of this group of seven elements disclosed that molyb- 

 denum was the needed micronutrient. The development of these 

 deficiency symptoms was prevented by adding 1 part of molyb- 

 denum as molybdic acid to 100,000,000 parts of nutrient solution. 

 After experimentally producing a characteristic deficiency syn- 

 drome and demonstrating that it could be prevented or cured by 

 the addition of molybdenum, the next step was to show that this 

 effect was peculiar to Mo and that other elements could not be 

 substituted. This was done by supplying the cultures with the 

 six other metals in the B7 solution and with the thirteen elements 

 in the C13 group. The deficiency symptoms persisted unless 

 Mo was provided. Neither was there any additional improve- 

 ment in growth when the application of Mo to molybdenum- 



