Table 7. Critical concentrations and the range of 



concentrations of several essential nutrient 

 elements in index segments of Ceratophyllum 

 demurs urn. 



Element 



N 



P 



Ca 



Mg 



K 



B 



study (Gerloff and Krombolz, 1966). The critical phos- 

 phorus concentration in the second one-inch was 0.10 per- 

 cent. A comparison of Tables 6 and 7 shows that the 

 critical nitrogen and phosphorus concentrations were 

 somewhat lower in Ceratophyllum than in Elodea . This 

 probably is related to a higher stem to leaf ratio in 

 Ceratophyllum . 



The greatest difference in critical concentrations in the 

 two species was in potassium. The critical potassium 

 concentration in Elodea was only 0.80%; in Ceratophyllum , 

 it was 1.70% or slightly more than double the Elodea 

 value. Only further experimentation can determine if 

 this difference is significant in terms of growth and 

 distribution of the plants in lakes and streams. 



22 



