1.0 2.0 30 4.0 5.0 6.0 



Tissue content of N (%) 



Figure 2. The relationship between yield and total nitrogen 

 content of the first and second one-inch terminal segments 

 of Elodea occidentalis grown in solutions of varying 

 nitrogen content. 



and also as a result of senescence and non-nutritional 

 abnormalities in the older tissues made the terminal one- 

 inch segment an unsatisfactory index region. This was 

 supported by unreported results which showed that in plants 

 which had been very deficient in nitrogen for a consider- 

 able period, the nitrogen content of terminal one-inch 

 segments was actually above the critical level, apparently 

 due to re-export from extensive regions of older, dying 

 tissues. 



15 



