Rothamsted Symposium on Trace Elements 



calities other mineral elements have been discovered and before the 

 last war Bobko and Belwousow developed the hypothesis that all 

 elements are present in plants though some of them in extremely 

 small quantities. Nearly all elements have been found in plant 

 ashes, but it has not yet been proved that they are all indispensible 

 for the nutrition of plants. At first it was assumed that accessory 

 elements, in small amounts, only stimulate plant growth. In the 

 case of many elements, as Paracelsus already stated, it is really 

 the question of the quantity present as to whether a substance acts 

 as a poison or as a stimulant. 



For water cultures refined methods of purifying salts and water 

 and the provision of suitable vessels have been necessary. It has 

 now been possible to prove that there are, in addition to the classi- 

 cal elements, still other elements essential for normal plant growth. 

 Just twenty years ago (1927) Miss Brenchley concluded that 

 boron in small quantities is essential for at least some of the higher 

 plants. She concluded further (1927) that copper compounds 

 were poisonous for higher plants except in great dilution, when 

 the element may exert a stimulating action. Since Miss Brench- 

 ley's work was published, it has been shown that copper is essential 

 for many species, at least in some stages of their development. 

 Miss Brenchley also concluded (1929) that in soil cultures many 

 plants respond to zinc salts, and it is now certain— as for manga- 

 nese and molybdenum-that both copper and zinc are essential for 

 many plants. 



There are perhaps still other mineral elements (Ti, Al, Rb) 

 essential for plant growth. But plants absorb and accumulate 

 elements, which are very probably without importance for their 

 nutrition. We have shown in our laboratory that many plants 

 absorb and accumulate gold, though it is not essential for them. 

 It can in great dilution stimulate the growth of some plants (Zea 

 Mays'), but plants grow well without it. The soil, where we have 

 collected our plants (Oslany in Slovakia), contains in 100 tons 

 only 2 g gold, but 10 kg ash of Equisetum folustre contains 0.61 g 

 gold. A comprehensive paper on gold in living organisms has 

 been published in Microchimica Acta by T. Babicka (Vol. 5, 

 1943). 



Investigations on essential trace elements are of considerable 

 importance in agriculture. There are localities where the soil is 

 very low in these elements and plants grown on such soils appear 

 sick. The effect of addition of boron, copper, zinc or manganese 



