The nearly vertical part of the hypothetical curve is 

 termed the "Deficient Zone"; here, plant yield is in- 

 creasing markedly, but the concentration in the organism 

 is changing very little. In the horizontal part of the 

 curve, organism concentration of the element is increasing, 

 but yield is not; this is the "Adequate Zone", or, more 

 commonly, the "Zone of Luxury Consumption". The "Transition 

 Zone" is that part of the curve between the zones of 

 deficiency and adequacy. Successful application of tissue 

 analysis depends on establishing for a species the critical 

 concentration for each element of interest. The critical 

 concentration is that content which is just inadequate 

 for maximum growth. 



Application of the plant analysis technique in evaluating 

 nutrient supplies for aquatic plants would require 

 establishing in laboratory experiments the critical 

 concentration for each potentially growth-limiting essential 

 element in the plant species of interest. The same species 

 then would be collected from lakes and streams, analyzed 

 for various elements, and the concentrations compared with 

 the critical levels. If a plant from the field contains 

 less than the critical concentration of an element, the 

 supply of that element was limiting growth in the environ- 

 ment from which the plant was collected. More growth would 

 result if greater amounts of the nutrient could be absorbed. 



The plant analysis technique seems particularly applicable 

 to evaluating nutrient supplies in aquatic environments 

 because of the difficulties in obtaining representative 

 water samples and in interpreting concentrations of 

 elements in terms of potential for plant growth. In 

 plant analysis, aquatic plants become the sampling devices 

 and the concentration of an element in plants reflects 

 all the factors which influenced availability of that 

 element in the environment from which the plants were 

 collected. 



The work to be reported was concerned with (1) development 

 of plant analysis as a simple procedure for evaluating 

 nutrient supplies in lakes and streams, (2) testing of the 

 plant analysis technique in nutrient evaluation in 

 representative Wisconsin lakes, and (3) development, 

 through laboratory studies, of an optimum culture medium 

 and general growth conditions for the culture of raacro- 

 phytes. The experimental work on this project will be 

 presented in three sections corresponding to the objectives 

 mentioned above. 



