130 TRACE ELEMENTS IN ANIMALS 



Miller and Byers (1937) distinguish three classes of plants in 

 regard to their capacity for absorbing selenium: (1) highly 

 seleniferous plants which absorb selenium readily and which are 

 either absent from or rare in neighbouring non-seleniferous areas . 

 Plants of this group include Astragalus bisulcatus, A. racemosus, 

 A. pectinatus, A. carolineanus, Stanleya pinnata, S. bipinnata, 

 Applopappus fremonti, Xylorrhiza parryi; (2) plants capable of 

 absorbing selenium, even in considerable amount, without 

 severe injury, but which are widely distributed on both seleni- 

 ferous and non-seleniferous soils. This group includes Aster 

 ericoides (white wreath aster), A.fendleri (blue aster), Gutierrezia 

 sarothrae (turpentine weed), Helianthus annuus (sunflower), Ag- 

 ropyron smithii (western wheat -grass) and the common cereals, 

 wheat, rye, barley and maize; (3) plants with a low tolerance for 

 selenium, which make poor growth at best on seleniferous soils 

 and which absorb only small amounts of selenium. Plants in 

 this group include Bouteloua gracilis (buffalo grass) and B. curti- 

 pendula (grama grass). 



For the control of selenium poisoning the relation of selenium 

 absorption to sulphur absorption by plants may be of great 

 significance. Hurd-Karrer (1934, 1935) showed that increasing 

 the sulphur content of the soil brought about a reduction in the 

 quantity of selenium absorbed by plants. Similarly, with plants 

 grown in water culture selenium uptake was reduced by in- 

 creasing the concentration of sulphate in the nutrient solution. 

 Hurd-Karrer and Kennedy (1936) found that grain from wheat 

 grown on soil containing 2 p. p.m. of selenium was toxic to white 

 rats, whereas grain from wheat grown on similar selenized soil 

 treated with flowers of sulphur or gypsum was not toxic, the 

 selenium content of the grain being reduced by such treatment 

 from about 12 p. p.m. to about 4 p. p.m. 



In 1937 Hurd-Karrer reported the results of experiments on 

 the uptake of sulphur and selenium by some fifteen different 

 crop plants grown in the greenhouse on soil artificially selenized 

 by the addition of 4 p. p.m. of selenium as sodium selenate. The 

 plants were known to differ widely with regard to their capacity 

 for absorbing sulphur. The shoots were cut when 1, 2 and 3 

 months old and the sulphur and selenium determined. The 

 results obtained after the first month are shown in Table XVI. 



