Re: What should my control be for my 'plant experiment'?

Mickey,

Yes, experiments need controls, and the general rule is that you need a control for each treatment. Now here is your problem, lights can be turned on and off and repositioned, but not gravity, unless someone is going to rent you some greenhouse space in the space station.

Let me help you refine your question a bit. First you are talking about the shoots reaction I think, after all roots might well react in very different ways to both light and gravity. Second, do you expect shoot to grow toward gravity? That's how it sounds.

So let's talk about simplifying your experiment. You put a plant, maybe a tomato or coleus, in a box and cut a hole in the side. And you put the plant on its side with its top toward the hole and shine a light through the hole. In a second box you put a similar plant but you keep it in the dark. This should tell you whether a shoot will grow toward the light (positive phototropism) more than it will grow away from the pull of gravity (negative geotropism). And you may want to fix a horizontal stick in the pot so as to have a frame of reference against which to measure the way the shoot is bending. Try that and let us know what happens.