We were discouraged by genetic improvement in photosynthesis per unit leaf area of tall fescue (Festuca arundinacea Schreb.) that did not result in higher yield. Further, root growth and carbohydrate storage were increased, providing further evidence that leaf growth was a primary sink and not source-limited. Improved leaf area production was desirable so we shifted to understanding its regulation which, due to leaf shape, is mainly elongation. Leaf growth zones of cell production, cell elongation and cell maturation were defined. Leaf elongation was more sensitive to environmental factors than was the leaf phyllochron such that final leaf size was related to elongation rate. Production of epidermal cells was associated more with leaf elongation than was their length. Elongation rate of epidermal cells tended to be similar among genotypes. Leaf growth is mainly due to cell production per initial epidermal cell. Mesophyll cells continue to divide even when adjacent epidermal cells are elongating, but stop dividing before epidermal cells stop elongation causing air space formation. Stomata form specific epidermal rows, but it is unknown why certain files develop stomata. Carbohydrate concentrations, especially low DP fructans, are high in the leaf growth zones, serve as a carbohydrate source and osmoticum, and are used after cell elongation ceases for synthesis of secondary cell wall. Similarly, N is accumulates in the growth zone, is used for various functions and then for synthesis of RuBisco. Minerals also accumulate in the growth zone and are reused later. It has been gratifying to learn these model principles occur in many grasses. It has been rewarding to be associated with the scientists who came to Missouri to expand the understanding of leaf growth in grasses. These scientists and their students are continuing to advance the knowledge and understand the importance of leaf growth rates.