The seed is nature's womb, the protective encasement of a limitless, cosmic recipe from which all manner of plant life is born. Although how the mighty oak tree grows from the frailest acorn remains an inspiring story of wondrous curiosity, the seed itself is a straightforward botanical structure. Actually a tiny plant, the seed is the mature ovule of a flower. The anatomy of the seed can be described by exploring the three main seed parts and two basic seed types.
Known as the testa, the seed coat or protective outer shell sheilds the embryo plant inside. Diseases and pests could easily destroy an unprotected embryo. Water can facilitate disease and hastens germination, creating the necessity for a covering to guard the dormant baby shoot from ill-timed moisture.
The endosperm contains food to sustain the immature plant. Much like our cells, this nutrient-rich layer may contain any combination of fats, carbohydrates or proteins. In addition, this layer provides the parental genetic contribution of chromosomes to the immature little plant. With a total of three chromosomes, two are mother-gifted and one is the father's contribution.
Suspended in an immature stage of development until nature wakes it from slumber, the embryo is the baby plant itself. Containing different layers depending on the type of seed, an embryo may have three to four distinctive parts. From the bottom up, an embryo may composed of the radicle (root), plumule (shoot), hypocotyl (stem) and cotyledon (leaf or leaves). The cotyledon also wraps around the embryo, further protecting it.
Monocotyledonous, nicknamed monocots, have only one cotyledon or immature leaf part. ("Mono" being the a prefix for "one.") Corn, cereal grains and grasses are all monocots. There are three basic layers of the monocot seed, including the seed coat, endosperm and embryo. The embryo plant itself is composed of the seed leaf (cotyledon) mentioned before, the plumule or initial shoot, and the root portion known as the radicle.
Known regularly as dicots, dicotyledonous seeds differ from monocots by virtue of their two immature leaves and a few structural distinctions. The basic parts remain the same, including a seed coat or testa and embryo. The dicot embryo contains the cotyledon, or double immature leaves, and also provides food in place of the endosperm. The plumule and radicle are both present representing the shoot and roots, but an additional plant part called the hypocotyl provides a stem for the developing plant. Examples of dicots include beans and flowering plants that have mature parts in sets of four or five.