References:

Plants and People, pages 87-91.

On Food and Cooking; pages 226-263.
 

What is a caryopsis?

What is a legume?

What is a grain?

How do monocot seeds germinate?

How do dicot seeds germinate?
 

GRAINS are the fruits of grasses. The pericarp is fused to the seed coat in single seeded fruits (the seed coat comes from the integument and the pericarp is from the carpel). This type of fruit is a CARYOPSIS. We commonly call them grains.

Grasses are monocots. The term monocot is derived from the fact that the embryonic plant in the seed has one leaf. Seed leaves are called COTYLEDONS. The single leaf of monocots is sometimes called the SCUTELLUM. The endosperm in grains is the nutritive tissue for the embryonic seed, and it is what we are seeking when we harvest grains. Corn is generally used as the representative of a monocot seed. A corn grain consists of a pericarp, endosperm, a radicle and a plumule. The layer on the outer part of the endosperm in grains is the ALEURONE, whose cells contain a rich reserve of oils, minerals, protein and vitamins. When grains are processes, the pericarp is removed from the endosperm, and we call the part including the pericarp and the aleurone the BRAN and the part containing the endosperm the GERM. There are a couple of other terms associated with seeds that refer to the position of the structure relative to the position of the cotyledon. The structures below the cotyledon, like the radicle, are part of the HYPOCOTYL. Structures above the cotyledons, like the plumule, form the EPICOTYL.

Monocot seeds have protective layers at the tip of the radicle and the tip of the plumule to protect the apical meristems there. The protective structure covering the tip of the radicle is called the COLEORHIZA and the structure protecting the tip of the plumule is called the COLEOPTILE.

When monocot seeds like corn germinate, the seed stays in the ground, the radicle grows down and the plumule grows up. The radicle forms a primary root that supplies the plant until the fibrous root system begins to develop, and then the primary root dies.

Legumes are dicots, as the embryonic plants in seeds have two leaves. Legumes in general also do not have endosperm as nutritive tissue for the young plants. Instead, the endosperm never really develops, with the nutritive tissues forming in the seed leaves, the cotyledons. A typical bean seed will have a seed coat, two large cotyledons, perhaps some other small cotyledons forming the epicotyl and the radicle forming the hypocotyl.

When dicot seeds like a bean germinates, the seed comes out of the ground (as most of the seed is in fact leaves). The radicle grows down to form a primary roots, which could develop into a tap root. The two large first cotyledons provide food for the young plant until it's regular leaves can make enough food.

"All flesh is grass"

The seeds of grasses and legumes are the basis of our civilization, and have been since human civilization began. In developing countries, over 75% of caloric intake can be in the form of grass and legume seeds. Even in developed countries, where more meats, for example, are consumed, the animals from which the meats are taken themselves derive their nutrition from grasses and legumes.

Seeds are small packets of concentrated energy that can be stored for long terms and transported long distances without spoilage. It is relatively easy to cultivate large numbers of grass seeds over relatively short times. In short, small numbers of people can cultivate the caloric requirements of large numbers of people, who are then free to do other things (rather than find and/or grow food).

There are over 8000 species of grasses, of which, only a handful are cultivated on a large scale.

Wheat

One of the oldest of cultivated grasses, there are over 30,000 varieties of wheat. Wheat was the most important crop of the ancient civilizations of the middle east. As wheat cultivation requires a degree of political stability to allow for the large fields and storage facilities needed, wheat cultivation declined in western Europe from the fall of the Roman empire until about the 19th century. Wheat grows best in dryer, cooler climates, and does not like moister regions. Wheat is the staple crop in north america.
Wheat, when ground up and mixed with water, forms an elastic material called GLUTEN. When mixed with yeast, this material will expand as the yeast produce carbon dioxide gas, and "raise". While rye grasses will also produce a gluten when their grains are mixed with water, it is inferior to wheat. Only wheat allows for the production of raised, "leavened" breads.

Rice

There are over 2500 different varieties of rice. Rice is the staple for over 50% of the world's population. Rice is grown principally in the monsoonal areas of eastern asia and Oceania. Unlike wheat, which does not like areas such as that in Mississippi, rice does quite well in such areas, and areas of the southern Mississippi River region are major rice producers. We commonly think of rice growing in standing water, however such standing water is not necessary for rice production. The purpose of water in rice fields is to drown out weedy competition.

Corn

Corn is the principle grain crop of the new world, and has been cultivated in the new world since at least 3500 BC. Corn is a fundamental food crop in the United States, although most of the harvest is used in meat, egg and milk production (i.e. feed for cows and chickens).

Legumes

Legumes are the second most important plant to human civilization, next to grasses. Seeds of legumes contain more protein than do those of grasses. The importance of legumes is well represented by the fact that prominent Roman family names are names of legumes; Cicero (chick pea), Fabius (faba bean) and Piso (pea). Lentils have been cultivated since at least 7000 BC in the near east, and beans have been cultivated in the new world since at least 6000 BC.