501- 



40 



O) 30 



<f> 



O 



0> 



v_ 



C 20 



c 



< 



10 



Light intensity (ft. candles) 



Figure 4 . The growth of Elodea occidentalis , as length in- 

 crease, during periods of exposure to various light 

 intensities . 



The limitations of using length increase as a criterion 

 of growth must be recognized. Nevertheless, from the 

 data obtained, maintenance of a specific light intensity 

 does not seem critical in macrophyte culture. Elodea 

 made reasonably good growth over the range of light 

 likely to be available in artificially lighted growth 

 chambers. On this project, light intensities were main- 

 tained in the range of 800-1700 ft candles. 



As with terrestrial species, light intensity had a marked 

 effect on plant morphology and color. At the lower light 

 intensities, the Elodea was unusually dark green in 

 color and the leaves were thinner and the internodes 

 longer than in the plants grown at 1700 ft candles. 



48 



