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Inside Leaves And Roots
1. Photosynthesis Edgar Lee Masters. 1916. Spoon River Anthology “ Now every gardener knows that plants grown in cellars Or under stones are twisted and yellow and weak.”
We need to talk about photosynthesis if we are going to talk about leaf anatomy. Most students in plant science at this point in their careers will have a basic idea that light is very important to plants for a number of reasons. One of which is that it is important to plant growth. Plants need light. A little over 300 years ago, in one of the first carefully designed biological experiments ever reported, the Belgian physician Jan Baptista van Helmont (1577-1644) offered the first experimental evidence that soil alone does not nourish the plant. Van Helmont grew a small willow tree in an earthenware pot, adding only water to the pot. At the end of five years, the willow had increased in weight by 74.4 kilograms, whereas the earth had decreased in weight by only 57 grams. He incorrectly concluded that that all the substance of the plant was produced from the water and none from the soil or air! Toward the end of the eighteenth century, the English scientist Joseph Priestly (1733-1804) reported that he had accidentally hit upon a method of restoring air that had been injured by the burning of a candle. A living sprig of mint turned air that would not support a candle into air that would. Later Jan Ingenhouse showed that this process required sunlight. All horticultural plants, except edible mushrooms, require light to complete their life cycles. Through the process of photosynthesis, plants convert light energy into chemical energy, which they use for growth, development, and the maintenance of life. Light is also important to plants for pigment (color) formation, plant growth habit, plant shape, plant size, flowering, fruiting, seed germination, onset of dormancy, onset of plant hardiness, leaf movements, formation of storage organs, autumn coloration, and defoliation of temperate zone trees.
