108 THE FUNCTIONS OF 



deficiency of this element were most pronounced in the plants 

 grown in the solutions containing the highest concentration of 

 calcium (0-403 g. per litre), were less with a medium calcium 

 concentration (0-143 g. per litre) and were not observed with low 

 calcium content (0-042 g. per litre). The effects with potassium 

 were in the reverse order, the symptoms of manganese deficiency 

 being most pronounced with low potassium supply (0-026 g. per 

 litre), less with medium potassium supply (0-082 g. per litre), 

 and not noticeable in the plants supplied with the highest con- 

 centration of potassium (0-26 g. per litre). These results are 

 interpreted as suggesting that there is an antagonism between 

 calcium and manganese in their absorption, while there is none 

 between potassium and manganese. Other observations by 

 Swanback support this suggestion. Thus with a low supply of 

 calcium the dry matter produced by the tobacco plant cultures 

 was 6 times as much when manganese was not supplied as when 

 0-0054 millimol. per litre of this element was supplied to the 

 culture solution. With a high supply of calcium the reverse 

 resulted, the dry matter of the plants provided with manganese 

 being 3-5 times that of the plants not supplied with it. These 

 results are explained on the view that with low calcium supply 

 the manganese retards the absorption and utilization of calcium, 

 shortage of which results in the small amount of dry matter 

 produced, while with high calcium supply the antagonistic effect 

 of the manganese is insufficient to reduce the absorption and 

 utilization of the calcium to a low level while the favourable 

 effect of the manganese itself brings about an increase in growth 

 and so of dry matter produced. 



That calcium antagonizes the absorption and utilization of 

 manganese while potassium is indifferent is shown by deter- 

 minations of the manganese content of shoots and roots of 

 tobacco plants grown in the solutions containing the various 

 concentrations of calcium and potassium already mentioned and 

 0-0054 millimol. of manganese per litre. The- results are shown in 

 the following table. The values in the fourth and fifth columns 

 of the table are of what Swanback calls the 'translocation 

 quotient'. This is the ratio of the manganese content of the 

 shoot to that of the root and is supposed to give a measure of the 

 mobility or relative translocation of the manganese. They show 



