Shoots are negatively gravitropic, growing away from the gravitational field. Gravitropisms are caused by different auxin concentrations, with more auxins collecting on the lower side of the shoots or roots. How higher concentrations on the lower sides of both shoots and roots produce opposite effects are not clear. Biological Clocks Biological clocks, physiological systems that enables organisms to live in harmony with the rhythms of nature, trigger certain cells and hormones that are crucial in the growth and development if plants. These clocks aren't perfect though they are necessary to all plants.
Biological clocks help plants to maintain a steady and constant growth progression.
Biological clocks can exist in different parts of the cell in countless cells. This means different parts of the plant can grow and blossom at different rates instead of at the same time. For instance, a flowering plant, a sunflower, might grow to be very tall. When outside factors inter in to this equation things start to happen. For example, a flash of light signifies dawn for some plants like the morning glory.