Final answer:
The independent variable in Harrison's experiment is the type of soil, the dependent variables are the height and number of leaves of the roses, and the control is a separate group of roses grown in a standardized soil. The constants include factors like water, sunlight, temperature, and planting conditions.
Step-by-step explanation:
The independent variable in Harrison's experiment is the type of soil (potting soil, clay, sand, and soil found outside his yard), as this is the factor that is being changed or manipulated. The dependent variables are the height and number of leaves of the roses, as these are the variables that are measured and are expected to be influenced by the type of soil. The control in this experiment would be a separate group of roses that are grown in a standardized soil that is known to be suitable for rose growth.
The constants in Harrison's experiment would be factors that are kept the same across all groups of roses, such as the amount of water, sunlight, temperature, and planting conditions. These constants ensure that any differences observed in the dependent variables can be attributed to the independent variable (type of soil) and not other factors.