Summarizing the Data

Darwin measured plant height to represent evolutionary fitness. This is our response variable. The experimental treatment applied two types of hand pollination, either with pollen from the same plant (self-pollinated) or another plant (cross-pollinated); this is our explanatory variable. We want to explain the plant height responses as a function of differences in the experimental pollination treatment. There are 15 plants of each type that were planted in pairs. This is indicated by a factor with 15 levels, one for each pair.