6 HISTORICAL INTRODUCTION 



is essential for the normal growth of a number of plants. Thus 

 in 1931 Sommer found that the addition of small quantities of 

 copper induced a considerable increase in growth of sunflowers, 

 flax and tomatoes, while in the same year Lipman and Mac- 

 kinney found that flax and barley grown in water culture failed 

 to produce seed in complete absence of copper. Evidence has 

 also been presented by Anderssen (1932) in South Africa and by 

 Oserkowsky and Thomas (1933) in America indicating that 

 chlorosis and dying back of the branches of various fruit trees 

 result from a deficiency of copper. Further, a pathological 

 condition of cereals and some other plants known as ' reclama- 

 tion disease ', occurring in plants growing on reclaimed heath land 

 in Holland and elsewhere, was attributed by Sjollema in 1933 to 

 copper deficiency. In cereals exhibiting this condition the tips 

 of the leaves turn yellow or white while seed fails to form. 



In 1939, Arnon and Stout obtained evidence that molyb- 

 denum may be an essential element for higher plants. They 

 found that tomato plants exhibited pathological symptoms when 

 grown in a culture solution containing all the ordinary nutrient 

 elements along with manganese, boron, zinc and copper but 

 which was freed from all trace of molybdenum. The lower leaves 

 of the plants first developed a mottling; then dying of the. 

 marginal cells followed while the flowers fell without setting 

 fruit. The condition was prevented by the addition of one part 

 of molybdenum as molybdic acid in 100,000,000 to the culture 

 solution, while the pathological symptoms were removed in 

 the molybdenum-deficient plants by spraying the leaves with 

 a very dilute solution of molybdic acid. More recently, Stein- 

 berg (1941) concluded that both molybdenum and gallium are 

 essential for the growth of Lemna. 



So far only higher plants have been considered, but it is quite 

 clear that the same trace elements may be equally essential for 

 the growth of lower plants, at any rate of fungi. Indeed, the 

 necessity of an element for the growth of a fungus has in more 

 than one instance been demonstrated before its essentiality for 

 a higher plant has been claimed. 



The favourite species among the fungi for studies on mineral 

 nutrition has been Aspergillus niger. In addition to the 

 generally acknowledged mineral nutritive elements, with the 



