Leaves are elegantly crafted to harvest light, the energy source for food manufacture in photosynthesis (see chapter 8). This is typically fulfilled by the expansion of sheetlike blades, which must be thin and translucent to allow light to penetrate to their innermost cells. They must also be held in outstretched positions without the assistance of wood in their construction, because wood is opaque and heavy. The blade is frequently attached to the stem by a leaf stalk, or petiole, one of the advantages of which is to rotate the leaf blade to track the sun’s changing position over the course
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