Which of Mill's Methods Is Illustrated in the Following Passage

Short Answer

Which of Mill's Methods is illustrated in the following passage? If, in your opinion, the conclusion reached indicates that an inadequate hypothesis was employed, explain why and formulate a better hypothesis.
Eastlake planted sunflowers in 64 separate plots, varying soil composition with the absence or presence of six ingredients (potash, potassium, iron, etc.) with one plot for each possible combination. The sunflowers that grew invariably came in two sizes. Upon further investigation, Eastlake found that the larger plants were always in plots containing nitrate. As a result, nitrate has now become a standard ingredient in sunflower fertilizer.