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Experiments were conducted in controlled environmental chambers to study the effects of temperature on leaf emergence and leaf growth of main stem in winter barley (Hordeum vulgare L.) plants. Plants of the cultivar, Kikai Hadaka, were grown at constant temperatures between 12·5 to 27·5 °C. The leaf number on the main stems was counted (in Haun units) every day from the emergence of the third leaf until the emergence of the seventh leaf. The area was measured from the second to the sixth leaves on the main stems. The emergence of new leaves was a linear function of time at all temperature regimes. The leaf emergence rate increased with increasing temperature until an optimum temperature of 22·5 °C was reached and then decreased with further increasing temperature, but not significantly, compared with the peak. The leaf emergence rate per degree-day (DD) was slower with increasing temperature. The leaf growth rate increased with increasing temperature until an optimum temperature of 20·0 °C was reached and then declined with further increases in temperature. The leaf growth rate per DD had its maximum at 17·5 °C. The leaf emergence and leaf growth under different temperatures but at the same DD were different. The responses to temperatures for emergence and growth of barley leaves were different. These results suggest that a fully developed concept of the relationship of temperature to plant development and growth is an important aspect of increasing the accuracy of dynamic crop simulation models.