Use a different line showing averages for each of the treatments. There should be a total of 6 lines. Have students draw conclusions from their data and results. They should compare their experimental results to their original hypothesis. If their hypotheses are not supported by their results, encourage students to explore reasons for the lack of support.
Hypothesis testing involves an evaluation of the causes of patterns and observations.
One is not always correct about those causes at the outset. This section in progress. Several are listed below. Raven, P.H., R.F. Evert, S.E. Eichhorn. 1998. Biology of Plants .