Understanding the basic structure of a seed and the process in which it germinates is an important part of gardening. Seeds come in all different shapes and sizes, but underneath they all function in similar ways. Nurturing and understanding them from the beginning will help you become a successful gardener.
The formation of a seed completes the process of the reproductive cycle of a plant. From this point forward these seeds are left to nature or come into our hands where we must help provide the conditions they need to grow and produce.
Inside a seed is a tiny embryonic plant waiting to be awakened and grown, both to continue the process of reproduction and to be utilized by us as food. Seeds come to you containing enough energy to sprout, meaning that you as a gardener have to help provide and care for its other needs; air, light, water, and nutrients. What you see when you hold a seed in your hand is the external part; the hard outer coating that protects it from potentially damaging outside forces, such as pests, bacteria and fungus. This is called the ‘seed coat’ or ‘testa’, which can vary in thickness depending on the type of seed.
The ‘hilum’, which is the scar left from the connection of the seed to its parent plants, is visible if you look very close. It is easier to see on larger seeds like beans and peas.
Inside the seed
Hidden underneath the seed coat is the seed embryo, which is the immature plant that we as gardeners need to nurture through the process of germination and into maturity.
(Two above images from here)
Inside the seed are 3 basic parts that help it survive and grow. When the seed has been awaken by the initiation of germination, the first part to push through the seed coat is the ‘radicle’ or ’embryonic root’. This is a tiny root that splits the seed coat, eventually developing into the plant’s roots system. This leads the way for the seed to push forth it’s leaf parts, working toward the ultimate mission of finding sun/light for photosynthesis so it can start producing it own nourishment. Seeds contain a certain amount of nourishment inside, but this is used up in the growing process fairly quickly.
‘Hypocotyl’ is the part that will become the plant’s stem and the ‘plumule’ is the part that grows into the leafy part of the plant and where the first true primary leaves of the plant begin from. Both of these parts grow upward in response to the light.
‘Cotyledons’ are the part of the seed embryo that contains the first seed leaves that emerge from the seed. The cotyledon contains an adequate food source until photosynthesis, which will occur after the first set of true plant leaves emerge. A few days after this, the cotyledons sprout out and toward the light. The true primary leaves of different plants types don’t show their true shape until this point.
Some seeds have two cotyledons or seed leaves, which are fleshy and store food; these are known as ‘dicots’. Beans, peas and squash are all dicots. ‘Monocots’ have only one cotyledon; a few examples of this are corn, onions, and wheat. Monocots also have an endosperm inside, which is a food source for the seeds growth made up mostly of starches. We use this as a food source too, as wheat flour or corn meal.