Tree seeds are the beginning of a new tree, containing an embryo, a stored food supply, and a protective outer layer. This compact package is fundamental to a tree’s reproductive cycle, enabling the dispersal and establishment of new generations. Understanding how these seeds originate reveals the biological processes that underpin forest ecosystems.
The Basics of Tree Seed Formation
Tree seed formation begins with sexual reproduction, involving specialized male and female reproductive components. Ovules, the female structures, contain the egg cell, while pollen grains carry male genetic material. For fertilization, pollen must be transferred to the receptive female parts, a process known as pollination. This transfer can happen through various means, including wind, insects, or other animals.
Once a pollen grain reaches an ovule, it germinates and forms a pollen tube that grows towards the egg cell. Fertilization occurs when the male gamete from pollen fuses with the egg cell, forming a zygote. The zygote develops into an embryo, the rudimentary plant within the seed. Nutrients accumulate to form a food supply, often called endosperm, sustaining the embryo during initial growth. The ovule’s outer layers harden, forming a protective seed coat for dispersal and germination.
Seeds from Flowering Trees
Flowering trees, also known as angiosperms, produce their seeds within flowers. Ovules are located inside the ovary, part of the flower. After fertilization, the ovary matures and often enlarges to become a fruit. This fruit protects the developing seeds and aids dispersal.
Flowering trees produce diverse fruits, all enclosing the seeds. Examples include fleshy fruits like apples and cherries, with seeds embedded in edible pulp. Other trees produce dry fruits, such as winged maple samaras, hard-shelled oak acorns, or walnuts, where the seed is encased in a hard shell. Regardless of appearance, these fruits are where flowering tree seeds originate.
Seeds from Coniferous Trees
Coniferous trees (gymnosperms) differ from flowering trees; their seeds are “naked,” not enclosed within a fruit. Instead, they produce seeds within cones. Coniferous trees bear both male and female cones, often on the same tree.
Male cones are smaller and produce pollen, usually dispersed by wind. Female cones contain ovules on their scales. When pollen lands on a female cone, fertilization occurs, and ovules develop into seeds. Seed development can be lengthy, taking up to two years after pollination. Once mature, female cone scales open, releasing winged seeds for wind dispersal away from the parent tree.