The turning of plants towards the sun is called phototropism. I still remember how exciting
it was back in 1935 to learn about auxin, the hormone that is produced to cause cells to
multiply and increase in size on side away from sun, to cause plant to lean towards sun
and keep flowers facing sun. We could grow oat seedlings, crush them, and filter juice.
Then the juice could be made into a jelly, and tiny cubes cut out of gelatin, and placed
in contact with a new seedling. The seedling would become angualted away from the
loction of the auxin cube, and the angle produced was used as crude assay for
concentration of auxin in the jelly.
At the same time, we learned about ethylene gas being used to cause bananas to ripen.
Those were the days, my friend.