This model demonstrates a development of bud into twig in the middle area of Russia. In March-April the buds of deciduous trees are swelling. Gradually buds dehisce, young leaves that were folded inside of buds appear from under the scales and start to grow. The leaf area enlarge, the length of twig extends due to the terminal bud. By the middle of May leaves cover a majority of trees. When autumn comes a plant hormone (inhibitor of growth), abscisic acid, comes into leaves and stimulates an ageing and an abscission of leaves. Green chlorophyll is destroying while more stable yellow and orange pigments - carotenoids - remain and ensure autumnal colour of the leaves. A separating layer of parenchyma develops at the basis of the leaf, with time conductive fascicles are breaking by a wind or by a weight of the leaf. By the end of September leaves are pulled down. Animation is operated by the "Start"/"Stop" and the "Reset" buttons.