Influence of mean daily temperature (MDT;°C) and carbon dioxide (CO₂; μmol·mol^–1) on height and width (cm); growth index; leaf length and width (cm) and number; shoot fresh and dry mass (g); hue angle (h°); chroma (C*); International Commission on Illumination (CIE) L* color value of red oakleaf lettuce ‘Rouxaï RZ’ and green butterhead lettuce ‘Rex’.

Data represent the mean of two replications and cultivars with 10 samples. Analyses of variance for the effects of MDT and CO2 and their interaction are included below each cultivar mean. Within-column means of a given treatment with different letters were significantly different according to Tukey’s honestly significant difference test (P < 0.05).