Answer:
Nucleus, Breeder, Foundation, and Certified.
What is a seed?
One of the ways in which a plant produces another plant of its own kind is the seed. Just as birds lay eggs to reproduce their kind, the plant grows a seed that makes another plant.
The flower or blossom of a plant must be fertilized or the seed it produces will not grow. After the seed is fully grown, or mature, it must rest. The rest period varies among different kinds of seeds. Many of them will not grow until they have rested thru the winter.
Seed growth requires moisture, oxygen, and warmth. Light helps some plants start seed growth. If seed growth doesn't start within a certain time, the seed will die. When seeds are stored by man for future use, they must be kept dry and within a certain temperature range.
Seeds vary greatly in size, shape, pattern, and color. The seeds of different plants are made in different ways. There is one kind of seed, for example, that has the tiny new plant in the center. Around this is stored food which will tide the young plant over until it has developed roots and leaves and can make its own food.
If a seed is fertile, has rested, and has received the moisture, oxygen, and warmth, it begins to grow. This is called “sprouting” or “germination.” Growth often starts when moisture reaches the seed. As the seed absorbs water, it swells. As chemical changes take place, the cells of the seeds begin to show life again and the tiny young plant within the seed begins to grow. Most parts of the seed go into the growing plant. The seed cover drops off and the new plant grows larger until it matures and makes seeds of its own.
Seeds may be small or large. Begonia seeds are so small they look like dust. Coconuts are seeds which may weigh as much as 40 pounds! Some plants have only a few dozen seeds, while others, such as the maple, have thousands. There are special ways seeds are made so that they will be spread. Burr-type seeds hitch a ride on the fur of animals. Seeds that stick in mud cling to animals feet. Seeds contained in fruit are carried by man and animals. Some seeds have "wings" and are blown by the wind, other seeds float on water, and some are even "exploded" away from the parent plant!