TRACE ELEMENTS IN PLANTS 105 



the soluble and insoluble fractions the fresh material was frozen 

 by means of an ice-salt mixture and from this, in thawing, the 

 juice was expressed under a pressure of 1600 lb. per sq. in. applied 

 for 2J min. The expressed juice together with washings of the 

 press cake and muslin containing it were taken as containing 

 the soluble iron and manganese, the press cake the insoluble 

 fraction. 



A study of Table IX shows at once how the dry weight and 

 condition of the plants is related to the Fe/Mn ratio and not to 

 the absolute concentrations of these nutrients. Thus plants 

 growing in solutions containing 0-002, 0-250 and 2-00 p.p.m. 

 manganese respectively were all normal and possessed about the 

 same dry weight provided that in each case the ratio of soluble 

 iron to soluble manganese in the leaves was within the range 

 1-5-2-5. Whenever the ratio was outside this range pathological 

 symptoms tended to develop. 



If the ratio were above 2-5 the symptoms were of one kind, if 

 the ratio were below 1-5 the symptoms were of a different kind. 

 The former were thus those of a too high Fe/Mn ratio, the latter 

 of a too low Fe/Mn ratio. The first could be described either as 

 manganese deficiency or iron excess, the second either as iron 

 deficiency or manganese excess. The first sign of a too high 

 Fe/Mn ratio was a fading of the green colour of the lower leaves 

 which later developed into an intervenal yellowing on the basal 

 part of the leaves. Next the upper leaves showed a fading of the 

 green colour in the intervenal areas followed by the development 

 of small brown necrotic spots. Finally, the new leaves opened 

 with the necrotic areas already present, and these leaves might 

 fail to develop and fall, also stem apices might die. Roots showed 

 no visible symptoms apart from being smaller than those of 

 normal plants. 



The symptoms of a too low Fe/Mn ratio (iron deficiency, 

 manganese excess) were quite distinct from those just described. 

 The first sign was a slight brown discoloration of the roots 

 followed by yellowing and slight curling of the upper leaves. 

 As the condition developed the discoloration of the roots and 

 chlorosis of the upper leaves continued until the newer leaves 

 were almost white. The leaves curled downwards and sometimes 

 the midribs darkened and their tissue broke down. Large 



