What is in a Seed ?

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Feb 23, 2004

This article will take you through the developments taking place in a seed from the time it is planted until it starts to grow as a plant. On purpose the technical terms have been maintained, and a quick reference sheet has been provided with explanation of terms.

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A seed is basically a container which includes the endosperm (supply of food) and the plant embryo, both wrapped in a seed coat. The embryo consists of a hypocotyl (stem), a radicle (root), one or more cotyledons (seed leaves), as well as a plumule (preliminary young bud or growing point).

Germination
Under favorable conditions the seed will take up water and begin to swell. This is also referred to as imbibition which eventually will lead to the seed coat breaking. This process is referred to as 'seed sprouting' or 'germination'.

The conditions required for germination are typically adequate moisture, temperatures and light. The exact requirements vary by species and typically mimic the original climatic conditions in which the plants developed, e.g. some require cool temperatures to germinate while others do best in hot weather. Some seeds need light while others require darkness. For all, the process starts with imbibition of water, but some seeds require a lot more water than others.

Stratification and Scarification
Some seeds have evolved to protect themselves against adverse conditions by requiring a cold or warm period, stratification, before the seed will germinate. Perennials native to harsh winter areas will typically have stratification requirements to avoid the seeds being killed off by freezing weather shortly after germination. The required cool period to break dormancy ensures that the winter has passed prior to germination. Similarly, plants native to hot dessert type climates often require a hot period to germinate at the outset of winter.

Some seeds have developed a thick impermeable seed coat, requiring them to pass through animals, where it will be dissolved by the stomach acids. These seeds can have their seed coats scratched with knives by gardeners, or be soaked in acids, to copy the natural responses and facilitate germination. This process is called scarification. Other seeds have a very thin seed coat: peanuts, for example.

Once the seed coat breaks, the first part of the seedling to emerge is the radicle, an embryonic root. At this point germination ends and establishment begins.