An experiment will be conducted in which 20 pepper plants are randomly assigned to two groups. The plants in group 1 will receive the current fertilizer, fertilizer a, and the plants in group 2 will receive a new fertilizer, fertilizer b. All other growing conditions, including amount of sunlight and water, will be kept the same for the two groups. The growth of the pepper plants will be compared for the two groups. What are the experimental units in this experiment?.