Seeds are the offspring of an existing tree or plant and contain resting embryos, which are immature plants that can grow into a tree. "Seeds: The Yearbook of Agriculture 1961" states that seeds are created through sexual reproduction, which occurs when stamens and pistils form in flower buds and pollen is transferred from a stamen to a pistil, usually through insect movement or on the wind. Pollination is the activator for egg fertilization, growth and development into an embryo.
After the embryo is created, the seed begins to store food called endosperm and enlarges. When enlargement ceases, the seed dries out and becomes a dormant living organism, waiting for the right conditions for germination.
Healthy tree seeds contain everything needed to grow into a mature tree. The outer visible layer is a seed coat, which protects the embryo from mechanical injury, insects, parasites and disease.
Tree seed embryos contain one or more cotyledons that serve as leaves when the seed germinates. The embryo also contains the hypocotyl, which becomes the tree's root, and the epicotyl, which will shoot up from the seed and break through the ground.
Encased by the seed coat and surrounding the embryo is the endosperm, the food that the seed uses during germination until it can draw food and nutrients through the root and shoot systems.
Seed dispersal occurs in a variety of ways. Squirrels and other animals find seeds, carry them away and bury them for food in the winter. Those seeds that aren't eaten have a chance to germinate.
Birds eat tree seeds. A tough outer coating protects seeds as they travel through the bird's digestive system, and they are dropped undamaged in locations that can be far away from the parent plant.
The wind can catch tree seeds, blowing and tumbling them away from the parent tree.
Humans also gather seeds, planting tree seeds to create shade or food sources.
How Seeds Grow
Tree seeds remain dormant until optimal growth conditions are present. These conditions include the right temperature, light and moisture levels and can vary for each type of tree.
According to Washington State University Extension's Seed Germination website, absorption of water activates an enzyme in the seed, which increases respiration and causes the seed's cells to duplicate. As the seed grows, it expands and will eventually burst through the seed coat.
The hypocotyl (root) emerges first and helps to anchor the seed in place and draw nutrients from the soil. The epicotyl (shoot) emerges next and pushes up through the soil, expanding its cotyledons into leaves that seek light.
The young plant transforms light, carbon dioxide and moisture into nutrients through photosynthesis, providing further fuel for its growth into a mature tree.