12 



F. Species Differences 



The order of fission-product uptake by the different plant families is 

 Leguminosae> Solanaceae>Compositae>Gramineae for the tops and Leguminosae 

 >Gramineae >Conipositae>Solanaceae for the roots (142). Other workers report no 

 consistent differences between the lower and higher orders of the plant kingdom (79). 

 The calcium and strontium content of eight legumes was about three times that found 

 in eight grasses (138). The absorptive power of a given species for strontium is con- 

 sidered to be proportional to its absorptive power for calcium (17, 66). 



Characteristics of the root system may be very imiportant in determining the 

 uptake of radioisotopes from soil. Russian thistle can absorb strontium from a soil 

 depth greater than 3-1/2 feet (116). Since the plants of the grass family have rela- 

 tively shallow root systems, they will preferentially absorb nuclides occurring near the 

 surface rather than those placed at a greater depth. With a grass-clover mixture, 

 it was found that both the strontium content and the strontium-to-calcium ratio were 

 reduced 70 per cent by plowing under the surface contamination (72). More deeply 

 rooted crops showed only small effects from this deeper placement. 



Bicarbonate has differential effects on plant species, with beans taking up 

 lesser amounts of cations than barley in the presence of bicarbonate (32). Additional 

 interactions of plant species with rate of uptake, distribution, temperature, and 

 other factors are probably of minor importance when considering broad differences. 



