A Primer on Seeds
Seeds have sometimes been called the largest army in the world. Among the many kinds of seeds are the equivalent of gliders, paratroops, artillery, and infantry. This is the army of plant seeds.
Some have wing-like parts that enable them to glide in the wind. In some cases, the seeds are thrown out forcefully from the plant when they are mature. Other seeds roll and move by gravity, or are carried off by birds or other animals to distant locations.
Seeds mean survival for many plants but not all. Plants that produce seeds often have an advantage over those that don’t. In essence, seed-producing seeds have two options of reproduction—seeds and vegetative means—while non-seed producers must continue by vegetative means alone.
Seeds have been described as miniature plants in a protective covering with a food supply. In actuality, they are the site of the embryonic plant.
Seeds vary greatly in size. Some are so tiny they are almost dust-like with hundreds of thousands per ounce. Others are so large they can weigh up to 60 pounds in the case of the double-coconut. In between, we find all kinds of situations.
Most cacti seeds tend to be rather small. Those of succulents are often small to medium sized. In the case of cacti, the seeds must often be separated from the fleshy fruits.
The life span of seeds varies greatly. Peanuts and cucumber seeds are good for about a year. On the other hand, some seeds are very long lived. Those of the campeche, a type of acacia, have germinated after nearly a century. In some cases, tobacco seed buried in the soil germinated after nearly 40 years. In general, the life span for most kinds of seeds will fall somewhere in between.
The seeds from different kinds of plants have a natural variation in their germination rates. For some species, the rate will be high, while for others it will be low. A low germination percentage suggests that you will need more seeds to get healthy seedlings. For most plants, the germination rate continues to fall as the seed ages.
Let’s look at the various structures within seeds and see how they operate.
Seeds have their own structures, which aren’t always visible to the naked eye.
With large seeds, it may be possible to carefully cut them open to examine the
The seed coat is what we actually see when we look at a seed. This plays a major role in seed survival. It provides some means of protection from unfavorable dry spells. To some degree, this can act as a barrier against attack from insects and diseases.
The embryo of a seed contains at least five separate parts. The cotyledon/cotyledons are the part that becomes the seed leaf/seed leaves. When a seed germinates, the first single, bright green leaf or pairs of leaves that appear are derived from this part of the seed.
The hypocotyl is the part of the embryo plant located between the root and the cotyledon.
The radicle in the seed will produce the root. The plumule is the terminal bud of the embryo. This will eventually form the shoot. The seed also contains endosperm, which contains food or energy for the seed.
The various kinds of seeds may have slightly different arrangements of these parts. But, most seeds that gardeners deal with have all of these basic parts.
As indicated above, when seeds germinate, the seedling will have either one or two seed leaves. Those plants that produce a single seed leaf are known as monocots, while those that have two are dicots.
Quite a few of the succulents are monocots. Examples are Agave, Aloe, Dasylirion, Dioscorea, Dracaena, Dyckia, Gasteria, Haworthia, and Yucca. For the most part, all the other succulents as well as the cacti will have two seed leaves.
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