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CHAPTER 1
endosperm
cotyledon
embryo
Inside a corn grain
earlier. The embryonic leaves don’t expand until they are carried out of the soil by the lengthening stem. Cotyledons are attached to and are a part of the embryo, but their role is entirely different. Rather then growing, they progressively shrink as stored foods are transferred to the seedling. In bean plants, this can be watched because expansion of the lower part of the stem, called the hypocotyl (hypo-, “below”) elevates the cotyledons a short distance above the soil surface where, within a few days, they shrivel and eventually drop from the plant; the cotyledons’ food supplies have been spent. When plants elevate their cotyledons in this manner, it is called an epigeous mode of germination (epi-, “above”; ge-, “earth”). For many seeds, including the pea, the cotyledons remain buried in the ground during hypogeous germination. The seeds of flowering plants contain either one or two cotyledons. Botanists use this characteristic to subdivide the angiosperms into two major groups—the dicots (di-, “two”) and the monocots (mono-, “one”). Compared with dicots, monocots are believed to be the more recent products of plant evolution and include grasses, cereal grains (wheat, oats, barley, rice, rye), sugar cane, bamboo, palms, lilies, irises, and orchids. Dicots,