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I am a leaf on the wind origin11/7/2022 ![]() ![]() If we apply a similar reasoning to leaves, we can think of a trade off between the lamina shape and the petiole mechanical properties 22, 23. This results in a larger diameter and bigger roots to have a better resistance to bending and a better anchorage on the ground 17, 18, 19, 20, 21. For example, if a stem is transiently bent the stem stops its longitudinal growth and allocates its biomass to strengthen itself. As a result, plants optimize the biomass allocation to assure both growth and survival 15, 16. Plants are able to produce only a limited amount of biomass over time 14. Combined with other internal factors, such as optimal sap flow 13, mechanics may have led angiosperm leaves to today’s large diversity in shape. However, the ability to deploy leaves to sunlight 7, 8, 9 regardless of external factors, such as wind 10, 11 is crucial in plant survival 12. But from a simple mechanics perspective, one can expect that the most optimized leaf would have a large, flat, and stiff lamina to maximize the light capture, and a flexible petiole to avoid fracture 5, 6. In nature, trees have evolved to have many different leaf forms in terms of size, lobes, and orientation 4. The lamina appears to be green and flattened in a plane perpendicular to the stem, which is presumably configured to maximize the capture of sunlight 3. The petiole is a beam-like structure connecting the lamina to the stem, while the lamina is the major photosynthetic part in leaves. In trees, leaves have evolved to perform the photosynthesis function, and typical non-sessile leaves are composed of a petiole and a lamina. ![]() Although there are several photosynthetic pathways for different species 1, the fundamental step is the same: using light energy to transform water and CO 2 into sugar and oxygen 2. Photosynthesis is the principal mechanism for nutrition in plants. Lastly, we discuss leaf’s ability to reduce stress at the stem-petiole junction by choosing certain geometry, and also present exploratory results on the effect that seasons have on the Young’s and twisting moduli. In addition, we develop a simple energetic model to find a relation between geometrical shapes and mechanical properties ( EI/ GJ = 2 L L/ W C where L L is the laminar length and W C is the laminar width), verified with experimental data. A twist-to-bend ratio EI/ GJ is found to be around 4.3, within the range in previous studies conducted on similar species ( EI/ GJ = 2.7~8.0 reported in S. From tensile/torsional tests, we characterize the bending rigidity ( EI) and the twisting rigidity ( GJ) of 15 petioles of 4 species in the Spring/Summer: Red Oak ( Quercus Rubra), American Sycamore ( Platanus occidentalis), Yellow Poplar ( Liriodendron tulipifera), and Sugar Maple ( Acer saccharum). Leaves of the same species are found to be geometrically similar regardless of their size. In this study, we measure the shape of laminae from 120 simple leaf species (no leaflets). ![]() To survive in harsh abiotic conditions, leaves may have evolved to form in different shapes, resulting from a coupling between the lamina geometry and the petiole mechanical properties. drag) on the lamina, the petiole undergoes twisting and bending motions. From a geometrical point of view, a non-sessile leaf is composed of two parts: a large flat plate called the lamina, and a long beam called the petiole which connects the lamina to the branch/stem. ![]()
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