4 MINERAL SALTS ABSORPTION IN PLANTS 



the club mosses {Lycopodium spp.) and some members of the family 

 Diapensiaceae, from which derives the importance of certain of 

 these plants as sources of mordants for dyeing. Selenium is an 

 element which is absorbed to widely different extents by different 

 plants (Table 3). Some species of Astragalus growing on seleniferous 



Table 3. Amounts of Selenium Absorbed by Various Plants from Soil to 

 WHICH Sodium Selenate was added at a Concentration of 5 parts per 



million 

 (Hurd-Karrer, 1935) 



soils accumulate so much of it that animals eating them suffer from 

 selenium poisoning ("alkali disease"). Strontium is absorbed to an 

 appreciable extent by a number of plants, and may comprise 2-3 

 per cent of the total dry weight in exceptional cases. Crops which 

 accumulate large amounts of strontium are a potential health hazard, 

 since ^''Sr is a dangerous radioactive isotope, produced in nuclear 

 explosions, which, if deposited in the bones of animals may induce 

 leukaemia. 



The accumulation of iodine by seaweeds has been well known 

 since the element was discovered (in kelp) by Courtois in 1812. 

 Laminaria digitata accumulates iodine to a concentration of about 

 3000 parts per million of water, from a concentration of less than 1 

 part per million in the sea. Bromine, too, is taken up by seaweeds, 

 but it usually attains a somewhat lower concentration than iodine, 

 in spite of the fact that its concentration in sea water is appreciably 

 greater. A number of rare elements are accumulated to varying 

 extents by seaweeds; titanium, for example, is concentrated 10,000- 

 fold by Fucus spiralis, and 1 20-fold by Laminaria digitata. Altogether 

 about sixty elements have been detected in plants, and the list will 



