A student is studying the effect of fertilizer on fruit growth. He uses 6 tomato plants, placing each in a garden where they get equal amounts of sun and water. One plant is given no fertilizer, while the other 5 plants are given 5, 10, 15, 20, and 25 grams of dissolved fertilizer each day for 3 weeks. At the end of the experiment the tomato fruits are weighed.
What is the dependent variable in this experiment?