A seed can lay dormant for months, years, or centuries
(sometimes even longer), protected by its seed coat. It waits for the right environmental
conditions needed to germinate. Germination refers to the beginning of growth,
in this case from a seed. The ideal environmental conditions for germination include
temperature, growing medium, and moisture.
Within the seed is the plant embryo—the immature plant. The
embryo has all the characteristics of the plant it will become—root, stem, and
leaves—in miniature. During germination the radicle, or root, emerges and
pushes its way downward, using gravity, and grows and branches into the soil.
The stem pushes upward, toward the light, and its cells grow and elongate. The germination
process can be amazingly fast, taking place in a matter of hours, days, or
weeks, depending on the seed type.
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| Dissecting a Joshua Tree seed (Yucca brevifolia) |
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Joshua Tree seed embryo
(photos by Al Harris)
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The cotyledon, or seed leaves, emerge and provide nourishment
for the seedling (the endosperm provides a food source in monocots). The seed
leaves wither or drop off as the nourishment is consumed, until the first
leaves emerge and begin photosynthesis. At that point the seedling is on its
way to growing into a mature, self-sustaining plant.
Learn More:
Botany for Gardeners, by Brian Capon (Timber Press 2005). See Part I Growth, Chapter 1,
“Cells and Seeds: Basics and Beginnings”.
Pollination and Fertilization, derived from Pollination and Fertilization, by Robert
Bear and David Rintoul, for Open Stax, Rice University (Creative Commons).
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