2 HISTORICAL INTRODUCTION 



Pfeffer's stronger nutrient solution 



Calcium nitrate 40 g. 



Potassium nitrate 1'Og. 



Potassium dihydrogen phosphate 1-0 g. 



Potassium chloride 0-5 g. 



Water 3 1. 



Ferric chloride medicinal solution 3 to 6 drops 



Pfeffer's weaker solution is similar, except that the same quantity of these 

 salts is dissolved in 7 1. of water. 



Von der Crone's nutrient solution 



Potassium nitrate 10 g. 



Calcium sulphate 0-5 g. 



Magnesium sulphate 0-5 g. 



Calcium phosphate 0-25 g. 



Ferrous phosphate 0-25 g. 



Water 1 1. 



It will be noticed that, in addition to the elements given above, 

 Pfeffer's solution also contains chlorine, while Sachs's solution 

 contains not only chlorine, but sodium. While the general 

 opinion of plant physiologists for many years was that most 

 plants required neither of these elements, it was rather vaguely 

 held that some plants required sodium or chlorine in addition to 

 those regarded as always necessary. Thus Pfeffer (1900) re- 

 marked that probably no plant had been grown in complete 

 absence of chlorine, and he considered it uncertain whether a 

 minimum amount was essential or not. Miller (1931) considered 

 that experimental results had shown that under certain con- 

 ditions sodium had a definite effect on the growth of plants of 

 some species. 



So opinion on the mineral nutrition of plants remained during 

 the latter half of the nineteenth century. It was well established 

 that many elements, apart from those regarded as necessary, 

 were present in plants, but their presence was regarded as 

 incidental, due to their presence in the soil in which the plants 

 grew. But in 1897 G. Bertrand claimed that manganese was 

 constantly associated in the plant with an oxidizing enzyme, 

 laccase, and he came to regard manganese as an essential con- 

 stituent of the oxidase system. In 1905 he claimed that an 

 insufficient supply of manganese to plants brought about 

 diminution or cessation of growth, and that manganese was to 

 be regarded as an essential element. Much subsequent experi- 



