First let's start with a general overview of a plant's dvelopment. Just like humans, plants are composed of cells. The cells of plants differ from us human beings in the fact that plant cells, do not move around. What happens is that at the very tip ends of the leaves and roots, is what is called the apical meristem. These are groups of cells that keep renewing themselves. These cells become encased in rigid cellulose walls where they will develop into the different plant parts. If you look closely, you will see that even though you may have ten of the same type of plant growing, each one is slightly different. No two plants are exactly alike, even those grown under tissue culture are slightly different. This is because plants are effected by the environment around them. Everything, from the soil, to the weather conditions, amount of light and water received on each part of the plant determines how much it will grow and what flowering parts it will produce.
Before you can even get a seed, the plant needs to develop flowering parts. Most flowering plants are called angiosperms. They have male flowering parts which are the pollen grains and the female part is the embryo sac. If conditions are right and the pollen is viable, fertilization takes place and cell division begins in the embryo sac within an ovule.
This ovule is a little bit off-center because at first division, two daughter cells will be formed. The first daughter cell is small, mainly composed of cytoplasm that will keep dividing and creating cells that eventually will be the embryo of the seed. The second daughter cell forms a suspensor that also keeps creating and dividing cells, but this structure becomes elongated and is how the embryo will receive nutrients from developing nutrient tissues within the the seed. At this time, your root and shoot parts start developing. Roots will develop from cells near the suspensor and shoot cells by the embryo.
While all the cells are busy dividing in the embryo, they differentiate into three basic groups. Those groups are epidermal cells, ground tissue, and vascular tissues. Epidermal on the outside, ground tissue next on the inisde for food and water storage and the vasuclar tissue is in the very center of the embryo.
Once all three of these type of tissues have finished developing, then signals are sent for the embryo to develop generally two, but in some cases, only one leaf called a cotyledon(s). These are the first two leaves you generally see when the seed sprouts. They are not considered the first true set of leaves on a plant. Those will be the next set of leaves to grow and as the plant grows and develops permanent leaves the cotyledons will die back and fall off.
There is only one thing left for the development of a seed. The seed coat. These are a group of cells that surround the embryo and the cotyledons with nutritive tissues to survive. If you open a seed pod, before it is fully developed you can see the these soft tissues developing. When the seed coat is fully developed you will now have a seed that will be resistant to unfavorable conditions in the envirnonment and drought conditions. This one of the reasons why people can store seeds for many years and still have them sprout.
You have your seed now, but you still don't have a sprout. You won't have a sprout until certain conditons are met for that particular seed. Those conditions were genetically programed into the embryo at time of fertilization. Remember even though you may be holding a hard coated seed it is alive and living. It will start germinating when it senses changes such as water, temperature, and light. Once your seed feels the changes going on around it, the embryo starts developing again and usually a root will be the first thing to emerge from the seed coat then the cotyledons. Due to gravitational forces, the root will extend downward looking for nutrients from the soil and the cotyledons upward searching for light and air to produce nutrients and chlorophyll.
Now you finally have sprout. Get excited and shout for joy. Having a sprout means you now have the potential to have a fully developed plant someday. Your sprout will continue to grow. The apical meristem at both the root tip and the tip of the shoot will keep generating cells that will eventually form all the leaves, shoots, flowers, buds and all the other parts necessary for that plant to reproduce and have the potential to make more seed. Proper care and maintance of your new sprout will one day yield you a beautiful plant.
Glossary terms: angiosperm, apical meristem, cotyledon, cytoplasm, embryo sac, epidermal cells, ground tissue, ovule, pollen grains, suspensor, vascular tissue
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