MadSci Network: Botany |
It might be easier to use seedlings, such as bean, grass, corn, sunflower, etc. Seedlings seem to have a strong phototropism. Seedlings are also desirable because they do not have multiple stems as larger plants often do. A single stem makes measurement of the stem angle easier. The classic phototropism research by Charles Darwin used young grass seedlings at the stage before the first leaf has emerged from the coleoptile (see website under references). Having potted plants will probably be easiest. One plant per pot is desirable so you can have 3 to 5 plants per treatment. Pots are also easily rotated, which allows treatments such as rotating a pot 180 degrees each day, twice per day, or every other day to see if it grows staight up when given light from one side. Having light below the plant will require 24 hour per day electric light, such as a cool white fluorescent light system (Hershey 1995). The reason is that plants respond strongly to gravity (gravitropism) so the stem will grow away from gravity in the dark, so 24 hour per day light will be required to be sure the plant has a chance to respond to light all the time. References Charles Darwin's Tropism Experiments Hershey, D.R. 1995. Plant Biology Science Projects. New York: Wiley.
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