Hope investigated the effect of fertilizer on the growth of two plant species, horseweed and sand grass. The control and experimental groups for her study contained both species. All plants were the same height at the start of the study. The plants were grown in a restricted-access area on a sand dune in South Carolina and were watered regularly. Fertilizer was added to the soil surrounding the plants in the experimental group only. The graph shows Hope’s results. Explain how the data in the graph support the idea that genetic factors and environmental factors affect the growth of organisms.