Cover illustration: The inset cover image shows a greenhouse crop of tomatoes, Solanum lycopersicum, growing under diffuse light. Crop photosynthesis is enhanced relative to equivalent levels of direct light, primarily because there is a more homogenous horizontal and vertical distribution of light, but also because plants acclimate to develop a higher photosynthetic capacity of leaves in the middle of the crop and a higher leaf area index. See Li et al. (pp. 145-156).