In a study of lettuce growth. 36 seedlings were randomly allocated to receive either high or low light and to be grown in either a standard nutrient solution or one containing extra nitrogen. After 16 days of growth, the lettuce plants were harvested, and the dry weight of the leaves was determined for each plant. The accompanying table shows the mean leaf dry weight (gm) of the 9 plants in each treatment group.23


For these data, SS(nutrient solution) = 10.4006, SS(light) = 13.95023, SS(interaction) = 0.18923, and SS(within) = 11.1392.
(a) Prepare an interaction graph (like Figure 11.7.3) and discuss any patterns.
(b) Construct the ANOVA table.
(c) Carry out an Ftest for interactions; use α = 0.05.
(d) Test the null hypothesis that nutrient solution has no effect on weight. Use α = 0.01.