Subject: How does caffeine effect the growth of plants?

I am performing an inquiry investigation concerning the effects of caffeine on 
plant growth.  I plan on using 6 plants of the same type and using different 
liquids that do and don't contain caffeine.  What would be the best type of 
plant to use at this time of year in middle Georgia and what liquid substance 
should be used as a source of caffeine(tea, coffee, coke, etc.).  I know that 
powdered caffeine would be best but don't know where to find it.  How long 
should I measure the effects?(1,2,3 weeks?) What actually goes on with caffeine 
to cause any effect on plant growth if positive or negative?  I have found that 
it may effect the process of cytokinesis in some way. If you can, please explain 
more. Thanks!

Re: How does caffeine effect the growth of plants?