A greenhouse experiment to test growth rates in tomato cultivars was conducted using sterile soil mix and watering with sterile solutions of water and fertilizer. Following germination, half of the plants in each group were transplanted into soil that was obtained from a nearby agricultural field (nonsterile), the other half into sterile soil. After several weeks the plants that were transplanted into nonsterile soil exhibited a much higher growth rate compared to the plants transplanted into sterile soil. The most likely explanation for this result is
the plants transplanted into the nonsterile soil were inoculated with mycorrhizae.