Seeds Are Baby Plants

I've written about seeds in the past, but I wanted to write a bit more extensively about them here. It would seem that many view seeds as inanimate objects to some extent. We view them as relatively simple things, not the complex living objects that they are. All of us know that seeds sprout when we add the right ingredients, but we often fail to fully understand them. They look dry and lifeless to a great extent. Of course, that is wrong and understanding their complexity makes us better gardeners.
Seeds are composed of three basic parts; the seed coat, the endosperm, and the embryo itself - the baby plant. I write about seeds extensively in my newest book - The Nature of Plants: An Introduction to How Plants Work, but I'll provide a synopsis here. All parts of a seed have a purpose and they work together.
The seed coat is a covering - it is what we call bran. When you eat wheat bran, for example, you are eating only the coat of the wheat seed. Bran is high in fiber and low in nutrition because there is no reason for a plant to put nutrition into its seed coats. Seed coats protect the living and the nutritional parts of a seed against the vagaries of the environment. Some seed coats are thick and hard to penetrate while others are thin. This is an evolutionary phenomenon. Plants evolved to grow in harsh environments need to protect the embryo until just the right conditions arise to make it safe to sprout. Plants evolved to germinate in stable and "easy" conditions don't need a seed coat that is difficult to penetrate. Under favorable conditions, it would be foolish to have such a seed coat.  Evolution shapes every living thing to do what is most successful.
Some seed coats protect the living embryo for a long time - those plants that need special conditions in order to safely germinate. Some seeds will not germinate until they are exposed to cold temperatures - even some in Florida. If you've spent 100,00 years adapting to life with a cold winter, it would be suicide to have your children germinate and then freeze to death. Some seed coats are programmed to break down after the seed is eaten. The need to abrade the seed coat stems from an evolutionary decision that your children are better off not germinating under your shade, but further away - the distance a bird might carry it before defecating.
The endosperm in a seed contains all the nutrition the embryo needs to start life off properly. We eat seeds because of this nutrition. This is the "flour" we use in a grain of wheat and other cereals.  Mammals feed their developing offspring via their blood supply and a placenta. Birds use a yolk to feed their developing chicks. Plants use the endosperm.  Most moms and dads send their their kids off with what they'll need to stand on their own. Plants are no different. Plants, like orchids, that produce virtually no endosperm for their embryos, rely on things like mychorrizal fungi to do it for them. They also produce huge numbers of seeds that are largely viewed as expendable.  They are good with that, but most plants pack endosperm with their children to ensure that they have a high chance of success. The living embryo uses very little of the energy stored in the endosperm until triggered to begin the germination process, but it is there for the amount that is needed to keep the embryo alive and it ends up working with the embryo when the time is right.
The living part of a seed is the fertilized embryo. This embryo is the product of sex - the fertilization process that began with pollination. Plant embryos are really no different than those of animals. They are alive. Because of that, they have a baseline metabolism. They eat and breathe, and they are waiting patiently to be born. The embryo is the "germ" part of a wheat seed. Embryos exist in a somewhat state of animation until triggered to begin the germination process, but they are not "lifeless."  Some embryos can live in this state of animation for some time, but none can exist this way before eventually dying.  Vegetable seed companies put the packaging date and/or use-by date because of this. Too often, the sellers of wildflower seed fail to do so. Embryos die and seeds don't sprout once this happens. Though you can't see it, embryos in seeds are trying their best to carry on living in their state of suspended animation, but there is a limit to this. Here in Florida, where life is relatively simple in comparison to a desert or a clime with long/cold winters, most of our plants produce seeds that have little ability to wait for long periods before needing to germinate before they  die. That is why so many seeds, planted months after maturation, fail to sprout. Simply put, they have died.
Planting from seed, like I do here in my own landscape, requires me to plant soon after the seed has ripened. I've planted many a flat of seed right after maturation and then tried another flat 4-6 months later. Invariably, the second planting fails to produce seedlings while the first one did in large numbers. If you plant from seed, plant so-called "fresh seed" - no older than 3 months. Saving it for a more convenient time or when conditions seem more favorable for planting simply relegates your embryo-filled seed to an unnecessary death.  As Elvis Presley once sang: "Don't be Cruel."