Lettuce seedlings had similar shoot biomass and leaf area in both the protective and unprotective environments during the first 4 weeks of their growth. However, morphologically, there were striking differences in these two groups of plants. Seedlings grown in the protective environment had long, narrow leaves compared with those grown in the unprotective environment However, transferring these tender seedlings to and growing them in the unprotective environment for over 3 d diminished these morphological differences