Seeds are amazing storage containers that allow a plant to travel through space and time. Inside each protective casing is a tiny plant held in status until it is exposed to conditions that initiate development and growth, along with some stored energy (endosperm) for the plant to get started with.
The miniature plant inside often has either one “seed leaf” (cotyledon) in the case of monocots (monocotyledonous plants) or a pair of seed leaves in the case of dicots (dicotyledonous plants). Along with the seed leaf (or leaves), the miniature plant inside the seed shell also usually has a pair of growing tips (apical meristems), one at the top of the stem (hypocotyl) that develops into the first “true” leaves at the top of the sprout (shoot development), and one at the tip of the root (radicle) used for root development. Meristem cells are unusual in that they are a basic building block cell, that can differentiate to become different types of cells dependent on need and environment. Meristem cells can divide and generate new cells, an ability that becomes lost when they differentiate into whichever type of plant cell they ultimately become. Stems, leaves, roots and flowers all start as undifferentiated meristem cells that have differentiated into the different cells needed to form the plant parts and organs. Although meristem cells can transform into different cells, once a cell type is declared, it loses the ability to become one of the other types.
In a nutshell, a protective seed coat protects a tiny plant that already has a root, stem, and a leaf or two. The metabolism of the plant is slowed dramatically, and dehydration stalls development. The embryonic plant is well developed and alive in a viable seed. If the plant dies or is fatally malformed, then the seed is dead, and will not sprout. Some varieties of plant seeds remain viable for years, where others are best used the following season.
Under proper environmental conditions (temperature, light, etc.) moisture entering through small holes in the seed coat called the micropyles will induce sprouting. If the micropyles are deformed or blocked, germination may be difficult. To assist in sprouting such seeds, they may be soaked in water before planting, or a small nick may be made in the seed coating (scarification).A small cut opposite the “hinge” side of the seed can made to allow moisture to be absorbed. An alternative to cutting the seed coat is to weaken it by abrading the seed against a bit of sandpaper or emery-board.
As the dried plant takes up the water, it starts to grow. Since the tiny plant is no longer in stasis, it begins to need warmth, moisture, and air. Once seeds have started to sprout, they must either grow or perish.