Great question! You are correct- plant roots do grow in the direction of gravity, while the plant itself grows in the opposite direction. This has a special name and is called gravitropism. You asked about finding more information about this; I personally like this link, if you have access to the internet:herbarium , however, if you just search the term gravitropism on the internet or in your library, you should find plenty of information. It was an excellent idea for you to do an experiment to investigate this. If you turn your plant on its side, it should start bending upward and grow towards the sky, while the roots will still grow downward. Now there is one other factor you want to consider, called phototropism, which tells us that plants also like to grow towards the light. Therefore, if you have your plant in a window, the plant might grow towards the sunlight outside, which could skew your experiment. If you want to test gravitropism on its own, you might want to put the plants outside, where the sun will shine more evenly on the plant throughout the day.