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Despite their many shapes, leaves have certain things in common. "Leaves need to be much longer and wider than they are thick to intercept light for photosynthesis and allow gaseous exchange without losing too much water," says Dr Richard Waites from the University of York. "Leaves also need to withstand high winds, allow water to run off them easily and avoid being eaten by herbivores." The huge range of shapes demonstrates that there are many ways to solve such problems. "Other modifications to leaf shape might also be a response to climate," Waites says. However there are still mysteries to be solved. While flowers are finely tuned to suit their pollinators, leaves show variation. "If you could find all leaves from a single oak tree, you would see that no two are the same," Waites says. "This illustrates that while plants can build precise parts for a specific function with little variation, they can also exploit variation around a common theme. So far it is unclear why in one tree such variation is important."
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