There are two more sterile bracts called glumes. The fruit is called a caryopsis. The major portion of the food energy is stored as endosperm. The storage product is mostly starch, but grains also have moderate amounts of protein and some fats. See the table on page 166.
Many grasses are self-compatible annuals that invest a large portion of their energy as fruits.
Directions of selection of grains. One major way in which humans have modified grains is selection for grasses with tillers that mature synchronously. That way the plants all mature fruits at the same time, and a single harvest collects almost all the seeds produced. Humans also have selected recently for shorter plants that don't lodge so readily. This is especially important in wet tropical regions of the world.