obviously in need of verification, is the suggested copper 

 deficiency in northern Wisconsin lakes. This focuses 

 attention on the importance of trace elements in the field 

 nutrition of aquatic plants. Copper deficiency also 

 would be of some practical importance, because if that 

 element controls plant growth in certain lakes, limited 

 reductions in nitrogen or phosphorus pollution might not 

 improve nuisance conditions in those lakes to the degree 

 anticipated. 



Although the results presented suggest plant analysis is 

 a useful bioassay, the need for additional studies to refine 

 the technique is emphasized. Hundreds of investigations 

 have provided the information necessary to firmly establish 

 plant analysis as a procedure for nutrient assays in soils. 

 Undoubtedly, there will be unique aspects in applications 

 of plant analysis to aquatic plants and environments. 

 Further investigations of the most suitable index segments, 

 more precise establishment of critical concentrations, 

 and the determination of critical concentrations for 

 other macrophytes and algae seem worthy of immediate 

 study. 



37 



