MadSci Network: Botany
Query:

Re: Phototropism experiment--best way to grow and place plants

Date: Thu Apr 5 00:32:46 2001
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 986170472.Bt
Message:

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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