Abstract
The cell walls of E. crassipes roots show areas of strong coloration, which can range from light
brown through brown, blue, violet to blue-black, while the plants appear generally healthy. This work
describes the environmental factors which control the particularly noticeable blue colouration of the
roots. From studies conducted under defined conditions in growth chambers, substrate nitrogen
deficiency in the light produces an intense blue root colouration. Thus with nitrate or ammonium
deficiency of the nutrient medium E. crassipes can be considered a nitrogen monitor.
